Bowdoin Science Journal

Environmental Science and EOS

Carcinization: Is it Happening to Everybody?

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If evolution had a favorite body plan, it might just be the crab.

This idea lies at the heart of carcinization, which is the repeated, independent evolution of crab-like body forms across diverse crustacean lineages. The term, first coined by zoologist Lancelot Borradaile in 1916 as “one of the many attempts of Nature to evolve a crab,” carcinization has since become one of evolutionary biology’s most fascinating examples of convergent evolution. However, as McLaughlin and Lemaitre argue in their 1997 review, Carcinization in the Anomura – fact or fiction?, the phenomenon is more complex than a linear march towards “true crabs.” More recent research, in Wolfe et al. (2021), How to Become a Crab: Phenotypic Constraints on a Recurring Body Plan, reframes carcinization as a repeated evolutionary outcome shaped not only by natural selection, but by deep developmental and structural constraints.

Across decapod crustaceans, crab-like forms have evolved multiple times. Within the Anomura alone (Figure 1), a group that includes hermit crabs, king crabs, squat lobsters, porcelain crabs, and coconut crabs, independent lineages have converged on broadly similar morphologies: a widened, flattened carapace, reduced and folded abdomen (pleon), and a compact body plan adapted for seafloor life. Porcelain crabs (Porcellanidae), king crabs (Lithodidae), and the terrestrial coconut crab (Birgus latro) all appear, at first glance, to have independently become crabs (McLaughlin & Lemaitre 1997).

Figure 1. Convergent evolution of crab-like body forms (carcinization) across major decapod crustacean groups, including true crabs (Brachyura), porcelain crabs (Porcellanidae), hairy stone crabs (Lomisidae), and king crabs (Lithodoidea) (Wolfe et al. 2021).

McLaughlin and Lemaitre emphasize that these similarities reflect multiple independent origins rather than a single evolutionary trajectory. Crucially, they challenge older, linear interpretations of crab evolution, such as the idea that king crabs evolved directly from hermit crabs through a gradual transformation. Instead, they argue that “carcinized” forms evolve through a variety of anatomical routes and should not be interpreted as stages in a single progression toward a crab “ideal state.”

Wolfe et al. extends this argument by reframing carcinization as part of a broader pattern of phenotypic constraint and integration. Rather than viewing crab-like forms as independently assembled traits, they propose that key features, such as carapace widening, abdominal folding, skeletal reinforcement, and locomotor reorganization, are developmentally and functionally linked. This phenotypic integration means that once certain traits evolve, they bias the evolution of others, channeling morphology toward a crab-like configuration. In this sense, carcinization is not simply selection acting on isolated traits, but the coordinated evolution of an interconnected body system (Wolfe et al. 2021).

This perspective also helps to explain why crab-like forms are so recurring. A compact, flattened body provides clear ecological advantages, including protection through a reduced exposed surface area, improved maneuverability in complex habitats, and enhanced stability for seafloor locomotion. However, neither paper supports the idea that these advantages alone guarantee convergence. Instead, Wolfe et al. emphasizes that carcinization emerges from the interaction between ecological pressures and developmental architecture that constrains how bodies can be reorganized.

Importantly, carcinization is not a one-way evolutionary trend. Both McLaughlin and Lemaitre and Wolfe et al. highlight the existence of  “decarcinization”, which is the evolutionary loss of crab-like features. For example, frog crabs (Raninoidea) evolved more elongated, less compact body forms despite belonging to the true crabs, while the fossil crab Callichimaera perplexa displayed several unusual non-crab-like traits (Wolfe et al. 2021). Some lineages become more crab-like over time, while others revert toward more elongated or exposed body forms. This bidirectional pattern undermines any notion of evolutionary inevitability and suggests a changing landscape of morphological possibilities shaped by trade-offs between protection, mobility, and ecological specialization.

Fossil evidence further complicates the picture (Figure 2). Early crab-like fossils often display mosaic combinations of traits, involving partial abdominal folding, intermediate carapace shapes, or ambiguous limb structures, making it difficult to reconstruct a single pathway toward modern crabs. Wolfe et al. argue that these fossils support a stepwise and potentially repeated assembly of crab-like forms rather than a single origin of the “crab body plan.”

Figure 2. Fossil examples of crab evolution showing uncarcinized, carcinized, and decarcinized body forms across major decapod lineages. Uncarcinized forms include the more elongated, lobster-like body plans shown in A, C, and D. Carcinized forms, characterized by broadened carapaces and reduced abdomens, are shown in B and H-J. Decarcinized forms, which exhibit partial reversals away from the classic crab-like body plan, are shown in E-G. Together, these fossils illustrate how crab-like morphologies evolved repeatedly through time, while some lineages also lost or reversed key crab-like traits (Wolfe et al., 2021).

At the center of Wolfe et al. is a shift in how carcinization is interpreted. Earlier accounts sometimes framed it as evolution repeatedly “trying to make a crab,” implying a directional or goal-like process. Both McLaughlin and Lemaitre and Wolfe et al. reject this framing. Instead, they argue that crab-like morphologies repeatedly evolve because they can arise through relatively simple modifications of existing crustacean body plans, given how crustacean body plans are developmentally organized. Evolution does not aim toward crabs; rather, crab-like forms repeatedly arise because they are among the structurally available solutions to similar ecological challenges.

This has broader implications for evolution. Wolfe et al. suggests that carcinization is best understood as a case study in how constraints and integration can shape the predictability of evolution. In some contexts, evolution may appear highly repeatable, not because outcomes are predetermined, but because developmental systems channel variation along restricted and recurrent pathways. At the same time, the existence of multiple independent origins and reversals shows that these pathways are not exclusive or deterministic (Wolfe et al. 2021).

So, is carcinization happening to everybody?

Not exactly. Yes, in the sense that crab-like body plans have evolved repeatedly across independent lineages, suggesting strong functional and developmental biases toward this form. But no, because carcinization is neither universal nor inevitable. Many crustaceans never approach a crab-like form, and even within carcinized groups, evolution frequently reverses direction or produces only partial convergence (Wolfe et al. 2021, McLaughlin & Lemaitre 1997). Similar patterns of convergent evolution occur throughout nature, including the repeated evolution of streamlined, torpedo-shaped swimming bodies in sharks, dolphins, and ichthyosaurs in response to the limitations of moving through water (Futuyma & Kirkpatrick, 2017), illustrating how comparable environmental pressures can produce similar morphologies in distantly related lineages.

Ultimately, carcinization reveals something more subtle than a march toward a single optimal design. It highlights how evolution operates within a landscape shaped by ecological opportunity, developmental constraint, and historical contingency. The crab body plan is not evolution’s endpoint; it is a repeatedly accessible solution that emerges when different evolutionary paths converge on similar structural answers to similar problems.

Literature Cited

  1. Futuyma, D. J., & Kirkpatrick, M. (2017). Evolution (4th ed.). Sinauer Associates.
  2. McLaughlin, P. A., & Lemaitre, R. (1997). Carcinization in the Anomura—Fact or fiction? I. Evidence from adult morphology. Contributions to Zoology, 67(2), 79–123.
  3. Wolfe, J. M., Luque, J., & Bracken-Grissom, H. D. (2021). How to become a crab: Phenotypic constraints on a recurring body plan. BioEssays, 43(5), Article 2100020. https://doi.org/10.1002/bies.202100020

Cause of Sea Star Wasting Disease Epidemic Linked to Common Bacteria

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Fig. 1. Photo of a sunflower sea star (Pycnopodia helianthoides) in a kelp forest. (Mazza, Marco. The Independent, June 21, 2024.)

Since its emergence in 2013, sea star wasting disease (SSWD) has quickly spread along the west coast of North America, infecting dozens of sea star species from Mexico to Alaska and upending marine ecosystems. A variety of causes of SSWD have been proposed over the past decade, but no clear cause has been isolated for what is now considered one of the largest marine epidemics. Sunflower sea stars, or Pycnopodia helianthoides, are considered one of the most vulnerable species to SSWD, with billions dying from SSWD since its emergence. Although sunflower sea stars once inhabited the entirety of the west coast of North America, they are now considered functionally extinct in much of their southern range. Over 87% of the population has been lost in the remaining northern areas, earning the species a classification of critically endangered. The large-scale decline of sunflower sea stars due to SSWD has had a cascading effect on ecosystems, in which sea urchin populations have experienced uninhibited growth in the absence of predation. This ecological imbalance has led to the mass destruction of kelp forests and the creation of “urchin barrens” (locations where a previous kelp forest was destroyed by sea urchin overgrazing), demonstrating the profound impact SSWD has on kelp ecosystems and the species that rely on them.

After a series of exposure experiments and genetic sequencing tests of sunflower sea stars infected with SSWD, scientists identified the common bacterium Vibrio pectenicida as a causative agent (a pathogen that directly leads to disease, but may occur under the influence of other environmental or physical conditions) for SSWD. These findings may have lasting impacts on attempts to stem the spread and population losses caused by SSWD, including future efforts to recover the population of sunflower sea stars. 

Over the course of three years (2021-2024), scientists conducted a total of seven exposure experiments on sunflower sea stars. Using tissue extracts, coelomic fluid injections (an essential fluid similar to blood for sea stars that circulates immune system cells), and tank water from diseased sunflower sea stars, exposed sea stars were infected with SSWD. Healthy sunflower sea stars were collected in Washington state or raised at Friday Harbor Laboratories, and were first isolated in a 2-week quarantine period to ensure that collected stars did not develop SSWD after potential exposure in the wild. All exposure methods led to transmission of SSWD, with 92% (46/50) of exposed individuals displaying symptoms of SSWD. The disease stages were progressively categorized as “arm twisting,” “arm autonomy,” and “mortality.” Stars exposed to SSWD often died between 6 days to 2 weeks post exposure, usually within a week after showing the first symptoms of the disease. 

While using diseased coelomic fluid and tissue sample injections to infect healthy sea stars, scientists also utilized control samples, in which tissues or coelomic fluid from a diseased star were first treated with heat or filtered before injection into a healthy star. All 54 individuals injected with treated samples survived, with limited indications of SSWD. Most sea stars injected with untreated tissue (24 out of 26) or coelomic fluid (16 out of 18) samples from diseased stars contracted SSWD. The dramatic decrease in disease spread after heat treatment indicated that the causative agent (pathogen) of SSWD was likely cellular.

Fig. 2. Diagram of exposure experiment process using treated and untreated Vibrio pectenicida bacteria and diseased tissues. (Prentice et al., 2025)
Fig. 2. Diagram of exposure experimental process using treated and untreated Vibrio pectenicida bacteria and diseased tissues. (Prentice et al., 2025)

After identifying that the cause of SSWD was likely cellular, scientists genetically sequenced diseased sea star coelomic fluid and tissues from both in-lab sea stars and sea stars at field outbreak sites. Coelomic fluid from healthy stars and stars exposed to SSWD was also collected to contrast the microbes present in sea stars at all disease stages. After RNA and DNA analysis (particularly using 16S ribosomal RNA gene amplicon datasets), the most significant microbial difference between healthy and diseased groups was identified to be the bacterium V. pectenicida (r^2 ≥ 0.90), which was found in abundance in samples from stars with SSWD and was absent in samples from healthy stars. This difference in microbial presence allowed scientists to pinpoint V. pectenicida as a likely causative agent of SSWD. Small bacterial loads of V. pectenicida were found in healthy stars, leading scientists to propose that sea stars can remain healthy with low concentrations of V. pectenicida in ideal environmental conditions. This may indicate that outbreaks occur when environmental conditions (such as increasing temperatures) compromise the star’s immune system and allow the bacterium to flourish.

After genetic sequencing identified V. pectenicida as a candidate for the causative agent of SSWD, scientists conducted a series of exposure experiments using pure V. pectenicida cultures isolated from infected stars. When injected into healthy sea stars, V. pectenicida bacterium strains FHCF-3 and FHCF-5 cultures resulted in SSWD. Healthy sea stars were then injected with high (10^5 colony forming units) and low (10^3 c.f.u.) amounts of V. pectenicida strain FHCF-3 and heat-treated controls. 13 out of 14 stars injected with living bacteria all contracted SSWD and died, while all stars injected with heat treated (dead) bacteria survived. The disease progressed faster in stars injected with a higher concentration of V. pectenicida strain FHCF-3, with mortality occurring 6-11 days post exposure. Meanwhile, the group exposed to a lower concentration of live bacteria progressed through the disease more slowly, with mortality occurring 11-16 days post exposure.

Fig. 3. Chart of disease progression in sunflower sea stars using different methods of exposure to SSWD. Visual representations of disease symptoms are displayed below. (Prentice et al., 2025)
Fig. 3. Chart of disease progression in sunflower sea stars using different methods of exposure to SSWD. Visual representations of disease symptoms are displayed below. (Prentice et al., 2025)

After identifying V. pectenicida as a strong possible cause of SSWD, gene sampling was also conducted at field sites across British Columbia in May and October 2023. Although no individuals sampled at the five sites exhibited signs of SSWD or had V. pectenicida in May, V. pectenicida was identified in two outbreak populations in October. Vibrio pectenicida was found in 16% of healthy stars from visually unaffected sites, 74% of visually normal stars in outbreak sites, and 86% of diseased stars in outbreak sites. The analysis of a genetic database from southeast Alaska in 2016 during an SSWD outbreak also found V. pectenicida in both diseased and normal stars in outbreak sites but not healthy sites, suggesting that V. pectenicida also played a role in past outbreaks of SSWD. Scientists hypothesized that instances of Vibrio pectenicida in apparently disease-free stars may be due to exposure to other diseased stars in the wild. 

The discovery of V. pectenicida as a contributing cause of SSWD has strong implications for future research and conservation efforts for struggling sea star populations. V. pectenicida has been found globally (ranging from Australia to Asia to Europe to the US) from 2009-2019 in a variety of marine hosts, particularly in shellfish and bivalve aquaculture. Future research can focus on the mechanism of V. pectenicida as a pathogen, further distinguishing where the bacterium can be found, and modes of transmission both between sea stars and from prey shellfish populations. Scientists proposed that warming oceans due to climate change may make stars more vulnerable to outbreaks of V. pectenicida and other pathogens that thrive in warmer environments, which would support an observed trend between SSWD and warming water temperatures. Since sea stars respond to unfavorable environmental conditions (such as warming water) with similar symptoms to SSWD, it has been difficult to classify SSWD outbreaks. The discovery of V. pectenicida as a causative agent allows researchers to identify V. pectenicida as an indicator of SSWD in sampling, supporting the expansion of sampling across different environments and sea star species. This is essential for continuing to understand SSWD and crafting a response to protect struggling sea star populations and affected ecosystems. 

 

References:

Mazza, Marco. “How Sunflower Stars Can Save California’s Vanishing Kelp Forests.” The Independent, Santa Barbara Independent, 21 June 2024, https://www.independent.com/2024/06/21/how-sunflower-stars-can-save-californias-vanishing-kelp-forests/ 

Prentice, M.B., Crandall, G.A., Chan, A.M. et al. “Vibrio pectenicida strain FHCF-3 is a causative agent of sea star wasting disease.” Nat Ecol Evol 9, 1739–1751 (2025). https://doi.org/10.1038/s41559-025-02797-2

Co-pyrolysis of Biomass and RDF for Waste to Energy Conversion

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One of the primary concerns regarding fossil fuels today is not only their massive environmental impact but their persistent dominance in the energy field. Growing waste, pollution and energy consumption and demand all prompt the search for alternative, renewable energy sources, for example, biomass. Biomass waste includes agricultural residues, such as crops, crop residues, animal waste, and food scraps. All of these can be thermochemically converted into fuel, chemicals, and other biobased materials for various applications, simultaneously reducing the amount of waste going into landfills. Biomasses are also widely available, have high moisture and volatile matter content, presence of alkali metals in ash, and display a wide range of different physical and chemical properties.  

Refuse Derived Fuel (RDF) is another example of waste with high energy potential. RDF is mainly composed of plastic waste, paper, textiles, and wood, containing high organic matter content, giving it a high calorific value. RDF is a fuel produced from municipal solid waste that has been processed to remove non-combustible materials, like metals, glass, and other inorganic materials, leading to relatively stable chemical properties and low moisture content. In return, this gives it a high energy potential. RDF also has a higher energy content than raw municipal solid waste, making it a more efficient fuel source. It can be easily transported and stored, making it a convenient fuel source for energy generation in the cement industry or in energy plants. However, the direct combustion of RDF can be potentially unsafe, causing the emission of hazardous substances.  

 Magdziarz et al., 2024 examines the co-conversion of biomass and RDF, specifically through a process called pyrolysis. Pyrolysis is a thermochemical conversion process carried out in an oxygen-free atmosphere (typically in nitrogen or argon) at a temperature above 300–400 ◦C. This leads to the production of three main products: syngas, pyro-oil (liquid or “bio-oil”), and pyro-char (solid or “bio-char”). The distribution of product yields depends directly on the conditions of the process (operational parameters) including the temperature, heating rate, residence time of the volatiles, the particle size of the feedstock, type of feedstock or biomass, etc. The syngas may be useful in generating heat and electricity, while the solid bio-char may be useful as a soil applicant, aiding in carbon sequestration, water retention, and nutrient availability. However, the main focus of this study was to improve the quality and quantity of produced bio-oil, which can be used as a renewable alternative to fossil fuels.  

Co-pyrolysis of biomass and RDF was considered a “good solution”, as it helps reduce deposited waste and improves the quality of bio-oil produced by overcoming some of the challenges associated with the pyrolysis of biomass alone, such as poor bio-oil quality due to the presence of impurities. Additionally, the process supports the development of circular economy principles by reducing the dependence of fossil fuel resources. Previous studies focused on co-pyrolysis of biomass and plastics as opposed to RDF and found that minimizing the concentration of complex liquid compounds and heavy hydrocarbons improved the quality of syngas and liquid products. The addition of catalysts further improved bio-oil quality by increasing the content of hydrocarbons and reducing the content of oxygenated compounds in bio-oil. Pyrolysis of pure RDF can be problematic due to the formation of tar, wax, and other volatile organic compounds, causing equipment damage, reducing product quality, and increasing emissions.  

Additionally, Magdziarz et al., 2024 investigated two agricultural biomass feedstocks, rye straw (RS) and agriculture grass (AG), along with RDF, mainly composed of plastics. The pyrolysis process was conducted at 600 ◦C under a nitrogen atmosphere with a mass sample of 1 gram and residence time of 3 minutes. First, the pyrolysis of raw feedstocks was conducted to collect and analyze the properties of solid, liquid, and gas products. Then, co-pyrolysis experiments were conducted to investigate the impact of RDF addition on the properties of products with mixtures of 75:25 and 50:50 weight-percentage ratios (biomass to RDF mass ratio). Respectively, the samples were named: 75RS-25RDF, 75AG-25RDF, 50RS-50RDF, and 50AG-50RDF. RS and AG have similar physical and chemical properties, but AG contains a higher ash content and, consequently, lower volatile matter. Ash content and volatile matter both can influence the yield of products, as ash can catalyze undesirable secondary reactions (char oxidation or tar formation), reducing bio-oil yield, and higher volatile matter content generally correlates with the higher yield of gaseous products. The study analyzed the composition of volatile matter released during the pyrolysis process for both feedstocks and for the mixtures of biomass and RDF.  

In the case of the RDF sample, there were over 300 chemical compounds, while the biomass samples released about half as many chemical compounds. Therefore, the released analytes, especially forRDF, may be considered highly complex mixtures composed of compounds with different volatility.

Atomic Share for Biomass Samples by Percentage

For RS and AG as seen in the table above, the main group of compounds were oxygen compounds. Meanwhile, for RDF, hydrocarbons were the dominant volatile products, and the very low oxygen content for RDF (<2.85 weight%) resulted in a negligible CO2 content, unlike the biomass samples. For the four mixtures of biomass and RDF (75RS-25RDF, 75AG-25RDF, 50RS-50RDF, and 50AG-50RDF), the percentages of the groups of volatile compounds released were compared to the values estimated based on the linear model.


Atomic Share for Varying Mixtures of Biomass Samples by Percentage

In all four samples, the hydrocarbons and their oxygen derivatives were the dominant group of compounds released during co-pyrolysis. The release of hydrocarbons is arguably beneficial for increasing the application potential of volatile pyrolysis products that can be a type of alternative fuel. Hydrocarbons can enhance the energy value of the fuel and after additional treatment, can be used as by-products to value-added materials. The study also noted that the observed share of hydrocarbons released during pyrolysis was significantly higher than calculated from the linear model, which correlated with the addition of RDF to the biomass samples. The increased percentage of hydrocarbons also correlated with a simultaneous decrease in the relative share of other groups of compounds, especially oxygen compounds, as well as significantly lower CO2 content than expected from the linear model’s calculation.  

Yields of Bio-char and Bio-oil for Varying Mixtures of Biomass Samples

The yields of the bio-char and bio-oil phases are presented in Figure 5 above. The char yield for AG was higher (27.3%) than for RS (21.2%). The addition of 50% RDF to biomass decreased the char yields to 16.2% and 13.2%, respectively. Bio-oil yield was higher for RS (35.9%) than for AG (29.9%). Results from previous studies also show higher bio-oil yields and lower bio-char yields as RDF percentage increased. As predicted, co-pyrolysis of RDF with biomass gave a better synergetic effect for RS than for AG with the RS samples producing a higher ratio of bio-oil than the AG samples.The gas yield was calculated by the formula, 100% – char yield – liquid yield, and the pure RS and AG samples had similar gas yields at around 40%. The presence of RDF did not significantly influence gas yield for AG, but for RS (50RS-50RDF) decreased the yield by 13%. Gas yields consisted mainly of CO, CO2, H2, and CH4. The calorific value of gas from RS pyrolysis was higher than for AG. The addition of RDF for both biomasses (50RS-50RDF and 50AG-50RDF) decreased the content of CO and H2 and simultaneously increased the amount of CO2 and CH4 product. However, the study mentions that the gas yields from co-pyrolysis were not a concern, as the main goal was to obtain bio-oil. 

The main conclusions for the study were that for mixtures of biomass and RDF the content of oxygen in volatiles was significantly reduced, while the content of hydrocarbons was increased, and co-pyrolysis of biomass and RDF confirmed the benefits of RDF addition, which positively influenced product yields and quality. The co-pyrolysis of the AG and RS (waste materials) with RDF offers another method to contribute to circular economics and sustainable waste management. Co-pyrolysis of biomass and RDF may potentially be effective ways to convert waste into energy and produce useful bio-char, bio-oil, and even various gaseous products. Future studies should focus on the type of feedstock used and various parameters of the pyrolysis process to ensure that the process is as efficient, sustainable, and environmentally friendly as possible.  

 

References

Magdziarz, A., Jerzak, W., Wądrzyk, M., & Sieradzka, M. (2024). Benefits from co-pyrolysis of biomass and refuse derived fuel for biofuels production: Experimental investigations. Renewable Energy, 230, 120808. https://doi.org/10.1016/j.renene.2024.120808

Phytoplankton and Ocean Warming: Uneven Adaptations at the Base of the Marine Food Web

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Global warming is steadily transforming Earth’s oceans. Between 1901 and 2023, sea surface temperatures have increased at an average rate of 0.14℉ per decade (US EPA, 2016). This seemingly small thermal shift is enough to disrupt circulation patterns, alter nutrient availability, and restructure entire marine communities. As oceans absorb over 90% of excess atmospheric heat, they become both a buffer against and a victim of climate change (Climate Change, 2025). Among the many organisms affected by these changes, phytoplankton—the microscopic, photosynthetic organisms that drift near the ocean’s surface—serve as a critical case study. These single-celled producers are responsible for about half of Earth’s oxygen production, and they form the foundation of aquatic food webs, converting sunlight into chemical energy that sustains nearly all marine life (Hook, 2023). Therefore, understanding how phytoplankton respond to warming is essential for predicting the future of marine ecosystems.

Phytoplankton are highly sensitive to temperature fluctuations. Since their metabolic processes, growth rates, and enzymatic activities are temperature-dependent, even minor thermal changes can reshape their abundance and distribution. When waters warm beyond a species’ thermal tolerance, populations may decline or shift toward cooler regions (Barton et al., 2016). At the microscopic level, these shifts can cascade upward through the food web, reducing food availability for zooplankton, fish, and the higher-level predators that feed on them, such as sharks, whales, and seals. However,  one key question remains: can phytoplankton adapt to rising temperatures, or will their thermal limits determine the structure of future marine ecosystems?

Huertas et al. (2011) directly addressed this question through controlled laboratory experiments designed to measure the capacity of phytoplankton to evolve under warming. The researchers selected twelve species representing a range of environments—freshwater, coastal, open-ocean, and coral symbiotic systems—to test whether thermal tolerance varied among ecological types. To simulate long-term warming, they employed a “ratchet technique,” in which phytoplankton populations were gradually exposed to higher temperatures. Each population started from a single cloned cell to remove preexisting genetic variation. Then, the cell cultures were repeatedly grown and transferred into warmer conditions, forcing the populations to either adapt to the changes through genetic mutations or face extinction.

The results revealed striking differences among species. Freshwater species, such as Scenedesmus intermedius, exhibited remarkable resilience, adapting to temperatures as high as 40°C. Coastal species like Tetraselmis suecica and Dictyosphaerium chlorelloides tolerated up to 35°C, while open-ocean species such as Emiliania huxleyi and Monochrysis lutheri showed little to no capacity for adaptation. Coral symbionts (Symbiodinium species) demonstrated limited but detectable resistance, reflecting the thermal stress already observed in coral reef environments. Importantly, adaptation was not simply a case of short-term acclimation. The researchers found that resistant populations arose at different times across replicate cultures. This serves as evidence that adaptation stemmed from rare, spontaneous genetic mutations instead of physiological flexibility. Growth rates of adapted populations diverged significantly from their ancestral strains, confirming that true evolutionary change had occurred.

These findings carry major implications for understanding the ecological future of the oceans. If phytoplankton species differ so widely in their ability to adapt, warming will likely reorganize marine communities from the bottom up. Species capable of rapid genetic adaptation may dominate, while others could decline or disappear. This uneven resilience could favor smaller, faster-growing species, altering nutrient cycling and potentially weakening the ocean’s ability to sequester carbon. Because phytoplankton drive roughly half of global primary production, any restructuring of these communities could ripple through food webs, climate regulation, and fisheries.

While Huertas et al. focused on individual species in controlled conditions, Poloczanska et al. (2016) broadens this picture to the scale of global ecosystems. Their review synthesized nearly 2,000 observations of marine organisms responding to climate change, confirming that uneven adaptation is already occurring across taxa and ocean regions. On average, species distributions are shifting towards the north and south poles by about 72 kilometers per decade, and spring life-cycle events such as breeding or migration are advancing by four days per decade. Warm-water species are becoming more abundant, while cold-water species decline. Coral calcification, the process by which corals take in calcium and carbonate ions to build their exoskeletons, is weakening under combined warming and acidification stress. These patterns mirror the interspecific variability observed by Huertas et al.; some organisms adjust successfully to changing conditions, while others falter. Here, the broader conclusion is that climate change does not affect marine life uniformly—it selectively reshapes communities based on biological flexibility, dispersal ability, and evolutionary potential.

Fig 1. Global distribution of documented marine biological responses to climate change across major ocean regions (Poloczanska et al., 2016). Bars show the proportion of observed responses as consistent (dark blue), equivocal (light blue), or no change (yellow). Numbers indicate total observations per region; symbols identify taxa with ≥10 observations. Background colors represent regional sea-surface warming from 1950–2009 (yellow: low; orange: medium; red: high). Regions are defined by ecological structure and oceanographic features. eveal that climate-driven shifts in abundance, distribution, and phenology vary sharply across ocean basins—mirroring the uneven adaptive capacities described by Huertas et al. (2011).

Together, these studies illustrate both the mechanisms and the consequences of ocean warming. Huertas et al. provides mechanistic insight—showing that adaptation in phytoplankton depends on genetic change, and that some species are inherently more capable than others. Building off of this, Poloczanska et al. reveals how these species-level differences scale up, driving global shifts in abundance, distribution, and ecosystem structure. The two perspectives complement one another; laboratory experiments explain how adaptation might occur, while global syntheses show where and to what extent it already has.

As climate change accelerates, understanding the adaptability of foundational organisms like phytoplankton becomes increasingly urgent. Their evolutionary potential will determine not only the structure of marine ecosystems, but also the ocean’s capacity to regulate the planet’s climate. By linking experimental evidence with global ecological trends, researchers are beginning to map out a future ocean defined by winners and losers—a mosaic of adaptation, migration, and loss. The challenge ahead lies in predicting how these microscopic shifts will ripple through the web of life that depends on them.

References:

Barton, A. D., Irwin, A. J., Finkel, Z. V., & Stock, C. A. (2016). Anthropogenic climate change drives shift and shuffle in North Atlantic phytoplankton communities. Proceedings of the National Academy of Sciences, 113(11), 2964–2969. https://doi.org/10.1073/pnas.1519080113 

Climate Change: Ocean Heat Content | NOAA Climate.gov. (2025, June 26). https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content 

Hook, B. (2023, May 31). Phenomenal Phytoplankton: Scientists Uncover Cellular Process Behind Oxygen Production | Scripps Institution of Oceanography. https://scripps.ucsd.edu/news/phenomenal-phytoplankton-scientists-uncover-cellular-process-behind-oxygen-production 

Huertas, I. E., Rouco, M., López-Rodas, V., & Costas, E. (2011). Warming will affect phytoplankton differently: Evidence through a mechanistic approach. Proceedings of the Royal Society B: Biological Sciences, 278(1724), 3534–3543. https://doi.org/10.1098/rspb.2011.0160 

Poloczanska, E. S., Burrows, M. T., Brown, C. J., García Molinos, J., Halpern, B. S., Hoegh-Guldberg, O., Kappel, C. V., Moore, P. J., Richardson, A. J., Schoeman, D. S., & Sydeman, W. J. (2016). Responses of Marine Organisms to Climate Change across Oceans. Frontiers in Marine Science, 3. https://doi.org/10.3389/fmars.2016.00062 

US EPA, O. (2016, June 27). Climate Change Indicators: Sea Surface Temperature [Reports and Assessments]. https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature 

 

Airborne Bacteria: A Hidden Regulator of Ocean Blooms

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Context

Marine phytoplankton are microscopic algae integral to oceanic ecosystems and global biogeochemical cycles. They contribute significantly to the process of carbon displacement into the deep ocean and primary production, forming the foundation of the marine food web. However, these phytoplankton populations are vulnerable to various environmental and biological stressors, including temperature changes, nutrient availability, and pathogen infections. When a phytoplankton bloom collapses, bacteria consume their organic matter, a process that requires oxygen. The decay of the bloom and oxygen levels can deplete oxygen and lead to “dead zones” that can suffocate marine life (US EPA, 2013). Researching the components of bloom dynamics enables us to better understand their interactions as a foundation of the food web and regulator of oxygen levels.

 

Fig 1. Demise of a phytoplankton bloom over the course of a handful of days (Demise of a Phytoplankton Bloom, 2014)

One of the most abundant bloom-forming phytoplankton is Gephyrocapsa Huxley, a species of coccolithophore, a type of phytoplankton covered in calcium carbonate plates known for its widespread blooms in the ocean. While viral infections have long been recognized as a primary cause of phytoplankton bloom collapse, researchers have questioned whether bacteria could be another potential source of pathogenicity. Recent research regarding G. huxleyi phytoplankton suggests so.

 

Fig 2. Calcium carbonate plating on a coccolithophore phytoplankton (Briggs, 2021)

 

This groundbreaking study by Lang-Yona et al. investigated whether airborne bacteria could infect G. huxleyi blooms and be an explanation for bloom collapses. This research aimed to analyze atmospheric bacteria as an ecological regulator of phytoplankton populations, an often disregarded consideration in the dynamics of oceanic microbial interactions and climate models. Understanding these interactions is critical for predicting changes in marine ecosystems and their impact on global carbon cycles.

Methods of the Study

To explore whether airborne bacteria play a role in controlling phytoplankton populations, researchers collected air and water samples above a bloom of G. huxleyi in the North Atlantic. They conducted this work aboard the research vessel R/V Tara, using specialized instruments to capture airborne bacteria at different heights. These included high-volume air samplers and devices called cascade impactors, which were set up at different points on the ship, including the deck and mast. This setup allowed them to collect bacteria from various altitudes and better understand how microbes travel through the air (Lang-Yona et al., 2024)

Back in the lab, the team introduced the airborne bacteria into cultures of G. huxleyi to see what would happen. They carefully watched for signs of infection, such as a drop in the algae’s natural fluorescence (a sign they were losing their ability to photosynthesize), increased debris in the water (indicating cell death), and visible damage to the algal cells. When signs of infection appeared, they filtered out the bacteria from the cultures and grew them on a nutrient-rich surface called Marine Agar 2216. This step helped them isolate specific bacterial strains. To confirm that these bacteria were truly responsible for the infection, they then reintroduced them to fresh G. huxleyi cultures and checked whether the same effects occurred.

To track how the bacteria and algae interacted over time, researchers used a technique called flow cytometry. This method shines a laser through tiny droplets of water containing cells, measuring their size, shape, and natural glow. It allows scientists to quickly count how many algae and bacteria are present and determine how the infection is progressing.

Finally, they identified the bacteria using genetic sequencing and measured their presence in air and water samples with a technique called quantitative PCR (qPCR). This method detects and counts bacterial DNA, helping researchers understand how common these airborne microbes are in different environments.

Results of the Study and Implications

The study identified the airborne bacterium Roseovarius nubinhibens as a key bacteria capable of infecting and contributing to the collapse of G. huxleyi blooms. This bacterium was found to remain viable after atmospheric transport and effectively infects phytoplankton upon reaching ocean waters. The ability of R. nubinhibens to survive and remain pathogenic after airborne dispersal suggests a more dynamic role for bacteria in ocean-atmosphere interactions than previously recognized.

The ability of bacteria to be transported via wind patterns indicates a geologically vast and major mechanism that has previously been overlooked. The findings suggest that in addition to viral infections, bacterial pathogens may serve as natural regulators of phytoplankton populations, influencing bloom duration and oceanic carbon cycling. This discovery is particularly significant because phytoplankton blooms play a critical role in the global carbon cycle by taking carbon from the atmosphere, and upon death, sinking to the deep ocean where the carbon is stored. If bacterial infections contribute to bloom collapse and can be dispersed so vastly,  they may influence carbon fluxes in ways that need to be accounted for in climate models.

Previously, viral infections were considered the primary biological driver of bloom decline, but this study introduces airborne bacteria as an additional player in phytoplankton mortality. This raises important questions about how environmental factors such as wind patterns and ocean currents influence bacterial dispersal. Additionally, climate change may impact the spread of airborne pathogens, potentially altering bloom dynamics in unforeseen ways. A warming climate and shifting atmospheric circulation patterns could enhance or suppress the spread of algicidal bacteria, with cascading effects on marine ecosystems.

Furthermore, this research highlights the complexity of microbial interactions in the ocean. Many bacterial species exhibit “Jekyll-and-Hyde” dynamics, shifting between mutualism and pathogenicity depending on environmental conditions and the physiological state of their algal hosts. In the case of R. nubinhibens, it is possible that under certain conditions, it exists in a neutral or even beneficial relationship with G. huxleyi, but when environmental factors such as nutrient depletion or increased bacterial density trigger a shift, it becomes pathogenic. The study’s infection experiments demonstrated that R. nubinhibens could rapidly induce algal demise, suggesting a transition from a benign to an algicidal state. This aligns with previous findings that some marine bacteria can switch between cooperative and harmful interactions based on chemical signaling. Understanding these complex interactions is essential for developing a more accurate picture of microbial regulation in marine environments, as such shifts can significantly alter bloom dynamics and oceanic food webs.

This study provides new insight into the role of airborne bacteria in regulating marine phytoplankton populations, demonstrating that Roseovarius nubinhibens can contribute to G. huxleyi bloom collapse. These findings expand our understanding of ocean-atmosphere microbial interactions and introduce airborne bacteria as an important but previously overlooked factor in bloom dynamics. Incorporating airborne bacterial processes into ecological and climate models will be crucial for accurately predicting future oceanic changes. Further research is necessary to determine whether other phytoplankton species are similarly affected and how environmental shifts may influence the prevalence and impact of airborne bacterial infections on marine ecosystems. Understanding these dynamics is essential for assessing ocean health and resilience in a rapidly changing climate.

 

References:

Briggs, G. M. (2021). Coccolithophores, photosynthetic unicellular algae. https://milnepublishing.geneseo.edu/botany/chapter/emiliana-huxleyi/

Demise of a Phytoplankton Bloom. (2014, November 26). [Text.Article]. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/84797/demise-of-a-phytoplankton-bloom

Lang-Yona, N., Flores, J. M., Nir-Zadock, T. S., Nussbaum, I., Koren, I., & Vardi, A. (2024). Impact of airborne algicidal bacteria on marine phytoplankton blooms. The ISME Journal, 18(1), wrae016. https://doi.org/10.1093/ismejo/wrae016

US EPA, O. (2013, March 12). The Effects: Dead Zones and Harmful Algal Blooms [Overviews and Factsheets]. https://www.epa.gov/nutrientpollution/effects-dead-zones-and-harmful-algal-blooms

 

Sunshine, Sea, and Sunscreen: How ‘Eco-Friendly’ Choices Affect Marine Life

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Since the onset of the COVID-19 pandemic in 2020, international tourism has slowly been returning to previous levels. As of July 2024, an estimated 790 million tourists have traveled internationally, marking an 11% increase from the prior year and approaching the frequency of pre-COVID travel (Global Tourism Statistics). While this rise sounds promising for economic stimulation and cultural preservation, it also reintroduces the environmental impacts associated with tourism. In the Mediterranean, for example, tourists seeking to enjoy sunny beach days may unknowingly disrupt local ecosystems through their sunscreen use. Knowing how our consumption and product use impacts environmental systems is a key factor in being able to pinpoint where environmental degradation is coming from, and being able to stop it at the source. This raises the question: do “eco-friendly” sunscreens truly provide a safer alternative?

Pedro Echeveste, a researcher in marine microbial ecology and ecotoxicology at the University of the Balearic Islands, and his team have investigated this topic. Their 2024 study focused on commercial sunscreens and their chemical components’s impact on bacterial communities linked to Posidonia oceanica, or Neptune grass, a foundational species in the Mediterranean ecosystem (Echeveste et al., 2024).

Figure 1. Overview of all experimental results. The image shows all the different types of bacteria and epiphytes tested, and how their cell abundance shifted based on the type of sunscreen added to their system (Echeveste et al., 2024).

The study examined both heterotrophic bacteria (including Pseudomonas azotifigens, Marinobacterium litorale, Thiothrix nivea, Sedimentiacola thiotaurini, and Cobetia sp.) and autotrophic bacteria (Halothece sp. and Fischerella muscicola), as well as epiphytes—plants growing on the leaves of Neptune grass without being parasitic. These bacterial communities were cultured in artificial seawater at 25°C, with a 12-hour light/dark cycle and an initial concentration of 10^5 bacteria per mL. The research team added various concentrations of nanoparticles and sunscreens (0, 0.01, 0.1, 1, 10, and 100 mg/L) to each sample, exposing the bacterial communities for 72 hours.

Two commonly used inorganic UV filters, titanium dioxide (TiO₂) and zinc oxide (ZnO), were tested due to their prevalence in commercial sunscreens. The study focused on three sunscreen types: an eco-friendly SPF 50 without nanoparticles (SPF50E), an SPF 50 containing TiO₂ nanoparticles (SPF50), and an SPF 90 with both TiO₂ and ZnO nanoparticles (SPF90).

After the 72-hour exposure, the pollution concentrations that led to a 10% population decline (known as the EC10 value) were recorded. Titanium dioxide proved toxic to all heterotrophic bacteria, with Thiothrix nivea exhibiting a 10% decline at a concentration of 3.8 mg/L. Zinc oxide was comparatively less harmful, affecting only Marinobacterium litorale and Pseudomonas azotifigens at an EC10 of 1.39 mg/L for the latter.

The effects varied among the sunscreen types. The eco-friendly SPF 50 reduced phosphorus uptake by 30-50% in most bacterial species, a significant alteration that suggests interference with key nutrient cycles. The regular SPF 50, containing TiO₂, decreased alkaline phosphatase (APA) activity, an enzyme necessary for cell communication via dephosphorylation. Dephosphorylation—the removal of a phosphate group—is a critical process for signal transmission within cells. All sunscreens in the study also led to increased levels of reactive oxygen species (ROS), molecules derived from oxygen that may damage cellular proteins, DNA, and other essential structures. This data allows us to assume that any form of sunscreen, no matter the label as “eco-friendly”, or the SPF value, can impose degradational effects on our environmental systems via one mode or another.

All in all, These findings reveal that eco-friendly labels sometimes lack scientific backing, failing to account for subtle but important factors in maintaining environmental balance. Even the “eco-friendly” SPF 50 sunscreen altered bacterial populations, calling into question the validity of eco-friendly claims. 

As tourism resumes in coastal areas, the increased use of sunscreens—and thus UV filters—places greater pressure on marine ecosystems (Raffa et al., 2018). This rise in sunscreen pollution underscores the importance of studying the effects of “eco-friendly” sunscreens, as even minor shifts in bacterial populations can compound into substantial ecosystem changes when multiplied by millions of beachgoers. Achieving a truly eco-friendly sunscreen remains a challenge, but as consumers, what we can do is adopt a more informed and thoughtful approach to product choices. By balancing our personal protection needs with the planet’s health, we can work toward solutions that better align with environmental preservation.

 

References:

  1. Un tourism: Bringing the world closer. UN Tourism World Tourism Barometer | Global Tourism Statistics. Available at: https://www.unwto.org/un-tourism-world-tourism-barometer-data#:~:text=International%20tourist%20arrivals%20hit%2096,4%25%20less%20than%20in%202019 (Accessed: 28 October 2024). 
  2. Echeveste, P., Fernández-Juárez, V., Brito-Echeverría, J., Rodríguez-Romero, A., Tovar-Sánchez, A., & Agawin, N. S. (2024). Toxicity of inorganic nanoparticles and commercial sunscreens on marine bacteria. Chemosphere, 364, 143066. https://doi.org/10.1016/j.chemosphere.2024.143066
  3. Raffa, R.B. et al. (2018) Sunscreen bans: Coral reefs and skin cancer, Wiley Journal of Clinal Pharmacy and Therapeutics. Available at: https://research.ebsco.com/c/ceyvtd/viewer/pdf/db53bg7blv (Accessed: 28 October 2024).

 

Microplastic burden in marine benthic invertebrates depends on feeding strategies

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Microplastic pollution is a global issue effectively impacting all aquatic systems from the poles to tropical reefs. Current emission patterns project to around 35 – 98 metric tons of annual microplastic emission by 2030. Yet, this may only be an underestimation, as our current understanding of microplastic concentrations based on traditional sampling practices overlooks smaller debris (Lindeque et al. 2020, Borrelle et al. 2020). With this scale of rapid increase in concentrations, the implications of microplastic accumulation in marine systems have become an increasing concern. In response to this global concern, Adam Porter and his team looked towards the ocean’s floor to better understand how microplastics interact with dynamic ecosystems.

Microplastics emitted into the marine environment can adversely impact a wide range of processes from cellular metabolism to digestive functions, fertility, locomotion, and growth (Foley et al. 2018; Bour et al. 2018). Furthermore, bioaccumulation, or trophic transfer when contaminated prey is consumed by predators, magnifies microplastic burdens in organisms higher in the food chain. These above properties, in conjunction to the rapidly increasing environmental concentrations, highlight the pressing need to quantify how much microplastics marine organisms are ingesting.

Historically, our understanding of individual microplastic burdens has often assumed that levels of environmental contamination directly map onto their uptake by marine organisms. However, studies have found that this isn’t always the case. Other factors, such as feeding strategies and community composition, also impact a species’ uptake rate (Pagter et al. 2021; Bour at al. 2018). 

To bridge the mismatch of environmental concentration and individual burden, Porter et al. reviewed 412 studies on marine invertebrates from around the globe to investigate how different species traits could influence microplastic uptake. First, they gathered data from each study and assigned a geographic sector to each sampling site. Next, they evaluated each observation for a variety of variables, including feeding mode, position within the sediment, and wet weight (mass) of the individual. Then, Porter’s team used statistical tests to examine the potential influence each parameter had on plastic uptake with statistical analyses tests and visualized their findings. 

Geographically, the Pacific Northwest, Yellow Sea and Japan Trench, had the highest mean individual microplastic burden. In terms of animal class, the highest mean burden occurred in the Malacostraca class. Malacostraca encompasses common commercial species such as crabs and lobsters, which could have commercial implications on industries like lobster fishing and aquaculture. 

Of all the outlined parameters, feeding strategies had the greatest impact on microplastic uptake. Omnivores were shown to have the highest rate of uptake, followed by predators, herbivores, grazers, suspension feeders, deposit feeders, and lastly scavengers. These findings support the bioaccumulation theory, one of several hypotheses concerning microplastic uptake patterns (Wang 2014). According to the bioaccumulation theory, microplastics enter the food web through primary consumers like suspension feeders, grazers, and filter feeders. The plastic they retain in their systems will then be ingested by higher trophic levels like secondary and tertiary consumers that are omnivores,predators, and scavengers. Accordingly, the microplastic burdens would be highest in predators and omnivores, which matches the study’s findings.

In addition to the quantity of microplastics retained, feeding patterns were also found to influence the size and type of microplastics consumed were also different across groups. The most reported shape was fibers. The mean sizes of these fragments ranged from 0.2 micrometers to 17 centimeters, and herbivores in general retained the largest particles, but the precise mechanisms driving these patterns remain unclear.  

These findings precisely highlight our gap in knowledge of microplastic distribution amongst marine communities. As Porter et al. highlights, a holistic consideration of subtle processes related to feeding patterns is essential in fine tuning our understanding of how our world is changing. Thus, although the study describes general trends on a global scale, future research focusing on regional subtleties is important. Subsequently, applying these findings as policy is crucial, as many marine organisms are frequently consumed commercial species. Being major consumers of seafood, the microplastic accumulation in marine animals can directly impact humans. This is particularly concerning in context of our status as the apex predator, and therefore the final stop in the chain of bioaccumulation. As the microplastic burden in marine organisms is rising at an alarming pace, the need for action is more urgent than ever.

 

Works Cited

Borrelle, S. B., Ringma, J., Law, K. L., Monnahan, C. C., Lebreton, L., McGivern, A., Murphy, E., Jambeck, J., Leonard, G. H., Hilleary, M. A., Eriksen, M., Possingham, H. P., De Frond, H., Gerber, L. R., Polidoro, B., Tahir, A., Bernard, M., Mallos, N., Barnes, M., & Rochman, C. M. (2020). Predicted growth in plastic waste exceeds efforts to mitigate plastic pollution. Science, 369(6510), 1515–1518. https://doi.org/10.1126/science.aba3656 

Bour, Agathe, Carlo Giacomo Avio, Stefania Gorbi, Francesco Regoli, and Ketil Hylland. “Presence of Microplastics in Benthic and Epibenthic Organisms: Influence of Habitat, Feeding Mode and Trophic Level.” Environmental Pollution (Barking, Essex: 1987) 243, no. Pt B (December 2018): 1217–25. https://doi.org/10.1016/j.envpol.2018.09.115.   

Foley, Carolyn J., Zachary S. Feiner, Timothy D. Malinich, and Tomas O. Höök. “A Meta-Analysis of the Effects of Exposure to Microplastics on Fish and Aquatic Invertebrates.” The Science of the Total Environment 631–632 (August 1, 2018): 550–59. https://doi.org/10.1016/j.scitotenv.2018.03.046.   

Lindeque, P. K., Cole, M., Coppock, R. L., Lewis, C. N., Miller, R. Z., Watts, A. J. R., Wilson- McNeal, A., Wright, S. L., & Galloway, T. S. (2020). Arewe underestimating microplastic abundance in the marine environment? A comparison of microplastic capture with nets of different mesh-size. Environmental Pollution, 265, 114721. https://doi.org/10.1016/j.envpol.2020.114721

Pagter, Elena, Róisín Nash, João Frias, and Fiona Kavanagh. “Assessing Microplastic Distribution within Infaunal Benthic Communities in a Coastal Embayment.” Science of The Total Environment 791 (October 15, 2021): 148278. https://doi.org/10.1016/j.scitotenv.2021.148278. 

​​Porter, A., Godbold, J. A., Lewis, C. N., Savage, G., Solan, M., & Galloway, T. S. (2023). Microplastic burden in marine benthic invertebrates depends on species traits and feeding ecology within biogeographical provinces. Nature Communications, 14(1), 8023. https://doi.org/10.1038/s41467-023-43788-w 

Wang, W. -X. “Chapter 4 – Bioaccumulation and Biomonitoring.” In Marine Ecotoxicology, edited by Julián Blasco, Peter M. Chapman, Olivia Campana, and Miriam Hampel, 99–119. Academic Press, 2016. https://doi.org/10.1016/B978-0-12-803371-5.00004-7.

Getting the Big Picture: Satellite Altimetry and the Future of Sea Level Rise Research

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Anthropogenic climate change is drastically affecting the natural processes of the Earth at unprecedented rates. Increased fossil fuel emissions coupled with global deforestation have altered Earth’s energy budget, creating the potential for positive feedback loops to further warm our planet. While some of this warming manifests through glacier melting, powerful storm systems, and rising global temperatures, it’s estimated that 93% of the total energy gained from the greenhouse effect is stored in the ocean, with the remaining 7% contributing to atmospheric warming (Cazenave et al. 2018, as cited in von Schuckmann et al. 2016). This storage of heat in the ocean is responsible for oceanic thermal expansion and in combination with glacier melt is contributing to global sea level rise. Currently, an estimated 230 million people live below 1 m of the high tide line and if we do not curb emissions, sea level rise projections range 1.1 – 2.1 m by 2100 (Kulp et al. 2019, Sweet et al. 2022). Sea level rise’s global impact has thus been a prominent area of scientific research with leading methods utilizing satellite altimetry to measure the ocean’s height globally over time. 

Originating in the 1990s, surface sea level data has been recorded using a multitude of satellites amassing information from subseasonal to multi-decadal time scales (Cazenave et al. 2018). NASA’s sea level change portal reports this data sub-annually, recording a current sea level rise of 103.8 mm since 1993 (NASA). Seeking more information on the current trend of satellite altimetry, I reached out to French geophysicist Dr. Anny Cazenave of the French space agency CNES and director of Laboratoire d’Etudes en Geophysique et Oceanographie Spatiale (LEGOS) in Toulouse, France. Dr. Cazenave is a pioneer in geodesy, has worked as one of the leading scientists on numerous altimetry missions, was lead author of the sea level rise report for two Intergovernmental Panel on Climate Change (IPCC) reports, and recently won the prestigious Vetlesen Prize in 2020 (European Space Sciences Committee). 

When asked about recent advancements in altimetry technology, Dr. Cazenave directed me towards the recent international Surface Water and Ocean Topography satellite mission (SWOT) launched in 2022. SWOT is able to detect ocean features with ten times the resolution of current technology, enabling fine-scale analysis of oceans, lakes, rivers, and much more (NASA SWOT). Specifically for measuring sea level rise, SWOT utilizes a Ka-band Radar Interferometer (KaRIn) which is capable of measuring the elevation of almost all bodies of water on Earth. KaRIn operates by measuring deflected microwave signals off of Earth’s surface using two antennas split 10 meters apart, enabling the generation of a detailed topographic image of Earth’s surface (NASA SWOT). With SWOT’s high-resolution capabilities for topographically mapping sea level change anomalies close to shore, more accurate estimations for how sea level rise can affect coastal communities will be accessible in the future.

The figure above displays the difference in resolution between Copernicus Marine Service of ESA (European Space Agency) data and SWOT surface height anomaly data (NASA SWOT).

Finally, in light of recent developments in AI and machine learning, Dr. Cazenave noted the power of these computational methods in analyzing large data sets. The high-precision data provided by SWOT requires advanced methods of analysis to physically represent sea level rise changes, posing a challenge for researchers (Stanley 2023). A few recent papers have already highlighted the use of neural networks that are trained on current altimetry and sea surface temperature data (Xiao et al. 2023, Martin et al. 2023). These neural networks are then able to decipher the high-resolution data, enabling for a greater understanding of ocean dynamics and sea surface anomalies. Dr. Cazenave explained that the key questions to answer regarding sea level rise are: (1) how will ice sheets contribute to future sea level rise, (2) how much will sea level rise in coastal regions, and (3) how will rising sea levels contribute to shoreline erosion and retreat. With novel computational analysis techniques and advanced sea surface monitoring, many of these questions are being answered with greater accuracy. As we navigate the effects of climate change, combining science and policy will allow us to design multifaceted solutions that enable a sustainable future for all.

References

  1. Anny Cazenave​. European Space Sciences Committee. (n.d.). https://www.essc.esf.org/panels-members/anny-cazenave%E2%80%8B/
  2. Cazenave, A., Palanisamy, H., & Ablain, M. (2018). Contemporary sea level changes from satellite altimetry: What have we learned? What are the new challenges? Advances in Space Research, 62(7), 1639–1653. https://doi.org/10.1016/j.asr.2018.07.017
  3. Home. (n.d.). NASA Sea Level Change Portal. Retrieved April 24, 2024, from https://sealevel.nasa.gov/
  4. Joint NASA, CNES Water-Tracking Satellite Reveals First Stunning Views. (n.d.). NASA SWOT. Retrieved April 24, 2024, from https://swot.jpl.nasa.gov/news/99/joint-nasa-cnes-water-tracking-satellite-reveals-first-stunning-views
  5. Kulp, S. A., & Strauss, B. H. (2019). New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications, 10(1), 4844. https://doi.org/10.1038/s41467-019-12808-z
  6. Martin, S. A., Manucharyan, G. E., & Klein, P. (2023). Synthesizing Sea Surface Temperature and Satellite Altimetry Observations Using Deep Learning Improves the Accuracy and Resolution of Gridded Sea Surface Height Anomalies. Journal of Advances in Modeling Earth Systems, 15(5), e2022MS003589. https://doi.org/10.1029/2022MS003589
  7. Stanley, S. (2023, October 17). Machine Learning Provides a Clearer Window into Ocean Motion. Eos. http://eos.org/research-spotlights/machine-learning-provides-a-clearer-window-into-ocean-motion
  8. Xiao, Q., Balwada, D., Jones, C. S., Herrero-González, M., Smith, K. S., & Abernathey, R. (2023). Reconstruction of Surface Kinematics From Sea Surface Height Using Neural Networks. Journal of Advances in Modeling Earth Systems, 15(10), e2023MS003709. https://doi.org/10.1029/2023MS003709
  9. von Schuckmann, K., Palmer, M., Trenberth, K. et al. An imperative to monitor Earth’s energy imbalance. Nature Clim Change 6, 138–144 (2016). https://doi.org/10.1038/nclimate2876

Invasive Species: Ecological Shapeshifters?

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Watershed reeds of midcoast Maine provide a deeper look into the field of epigenetics

Forests, grasslands, and marshes are ecological battlegrounds. In the fight to hold territory, maintain access to resources, and reproduce, many organisms compete directly to occupy the same niche– the role played by a specific organism in an ecosystem. An organism’s ability to carry out these roles is dictated by its “fitness” or capacity to survive and contribute its genes to the next generation. Naturally, relative reproductive success is incredibly environmentally dependent. Most organisms are tailor-made to thrive within their native habitats via natural selection. However, this biological narrative is challenged by the proliferation of invasive species in competition with their native counterparts. In their 2016 study, Spens and Douhovnikoff argue that epigenetics may be key to understanding ecological invasiveness and that the common reed (Phragmites australis) is “an ideal model species” (Spens & Douhovnikoff, 2016) for studying this rapidly expanding subfield of genetics.

Among other things, greater phenotypic plasticity, or “the ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions” (Fusco & Minelli, 2010), increases an organism’s potential to adjust to its surroundings and occupy a vast variety of niches. This becomes possible through epigenetics.  Epigenetic modifications alter gene expression without changing the underlying DNA sequence (Weinhold, 2006). Methylation, the process by which methyl groups are added to DNA, is the key turning genes “on” and “off” (Menezo et al., 2020). The addition of methyl groups prevents DNA-transcribing proteins from accessing the DNA strand, stopping the gene’s expression as a protein. This has the potential to create significant differences in structural and even cellular function among individuals that are otherwise genetically identical.

Clonal plants provide a unique opportunity to study environmental pressures on epigenetics, as these individuals can act as their own genetic control. Reeds are an excellent example of this: as facultatively clonal plants, they can utilize both sexual and asexual reproduction. Exploiting this integral feature, and the existence of multiple subspecies of reed in midcoast Maine, researchers studied the genomes of both native and invasive reeds in two separate locations, Libby and Webhannet. They addressed two questions: Do introduced subspecies exhibit greater epigenetic variation (indicating that epigenetics plays a role in the success of an invasive species)? And will the variation between subspecies genotypes be lesser than the variation within a single genotype’s epigenetic markers (suggesting that epigenetic variation can be used to adapt to an incredibly variable environment)?

Researchers sought answers by studying clusters of reeds called ramets. Since all the reeds within a ramet were genetically identical, they could selectively measure epigenetic variation. These clones were grown within heterogeneous microhabitats that contain varying combinations of nutrients and conditions. Extracted DNA fragments were compared based on the level of methylation among subspecies, genotype, and ramet.

In both sites, the invasive reed demonstrated greater epigenetic diversity than the native reed (Figure 1). Up to 71% of epigenetic variation at the Webhannet site is attributed to differences among genotypes. These results suggest that clones adjust to the demands of their environments via epigenetics, rather than genotypic adaptation. Flexibility of this kind allows for rapid specialization in response to the hyper-individualized environmental conditions of each ramet. Additionally, each site developed an epigenetic “signature” with both subspecies exhibiting distinct, location specific, morphological characteristics. The significant differences in epigenetic markers between sites hint at the potential for large scale shifts due to epigenetics, should genotype not be a factor in these differences. The distinct characteristics displayed by each species demonstrate the vast alterations necessary to survive in an environment with subtle differences.

Figure 1. Epigenetic markers clustered by species (native, introduced) and location (Libby, Webhannet). Differences within a single genotype were greater than variation between genotypes, particularly for the introduced species. Figure adapted from Spens and Douhovnikoff

While this study was small scale, it supports the position that epigenotype variation provides a strong competitive advantage in the natural world. It also suggests that further study would provide more valuable information about the relevance of epigenetics in ecology. In our rapidly changing environment, due to climate change and other human influences, these native genotypes are in danger of being displaced from their niches. Despite a species’ history with its habitat, subtle alterations can have vast impact on individuals that demonstrate low plasticity or tolerance for change. Introduced organisms who demonstrate more flexible epigenotypes have the potential to outcompete their neighbors, eroding local ecosystems beyond repair. This reality drives ecological research in the direction of epigenetics, not only for the sake of discovery, but also in hopes of protecting species who cannot adapt as quickly as we disrupt.

 

Works Cited

Fusco, G., & Minelli, A. (2010). Phenotypic plasticity in development and evolution: Facts and concepts. Philosophical Transactions of the Royal Society B: Biological Sciences, 365(1540), 547–556. https://doi.org/10.1098/rstb.2009.0267

Menezo, Y., Clement, P., Clement, A., & Elder, K. (2020). Methylation: An Ineluctable Biochemical and Physiological Process Essential to the Transmission of Life. International Journal of Molecular Sciences, 21(23), 9311. https://doi.org/10.3390/ijms21239311

Spens, A., & Douhovnikoff, V. (2016). Epigenetic variation within Phragmites australis among lineages, genotypes, and ramets. Springer International Publishing. https://link.springer.com/article/10.1007/s10530-016-1223

Weinhold, B. (2006). Epigenetics: The Science of Change. Environmental Health Perspectives, 114(3), A160–A167.

Atlantic on the Brink: Climate Change Impacts to a Critical Ocean Circulation System

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Global warming due to anthropogenic greenhouse gas emissions poses an immense threat to Earth’s oceans, which serve as a vital climate regulation system. The influx of large quantities of freshwater from melting Arctic sea ice has the potential to critically alter ocean circulation in the North Atlantic. Changes to the physical properties of seawater in the North Atlantic could eventually lead to the collapse of the Atlantic Meridional Overturning Circulation (AMOC), an event that would result in potentially catastrophic changes to climate in the Northern Hemisphere. Predictive climate models have noted that this shift could occur in the future, developing a series of warnings that could help understand more accurately when this major climate shift could occur. Writing in Science Advances, Van Westen and colleagues report the findings of the Community Earth System Model (CESM) and their predictions regarding the impacts of the AMOC’s collapse.

Figure 1: A visualization of the Atlantic Meridional Overturning Circulation (Adapted from “The Ocean Conveyor – Woods Hole Oceanographic Institution,” n.d.).

The AMOC is a “tipping element” of Earth’s climate, meaning that it is very sensitive to changes in salinity and temperature and could have substantial, reverberating climate impacts if disrupted (Armstrong et al., 2022). Since 1950, oceanographic and climate data have displayed that AMOC strength has significantly decreased and is potentially in its weakest state over the past thousand years (Caesar et al., 2021). These changes largely result from an increased freshwater flux into the North Atlantic due to high rates of Arctic sea ice melting as a product of anthropogenic climate warming. This methodical increase in freshwater flux into the North Atlantic could eventually lead to the collapse of this critical ocean circulation system, an event that would have severe impacts on temperature and weather patterns, especially in the Northern Hemisphere. Prior predictive climate models, which fail to encapsulate Earth climate systems as accurately as the model used by Van Westen and colleagues, have not yet modeled an AMOC collapse. Van Westen et al.’s 2024 study is the first to definitively model this crucial climate tipping point.

Van Westen and colleagues performed their study in CESM version 1.0.5, a complex climate model that simulates earth systems (Danabasoglu et al., 2020). The research team set a preindustrial control simulation with corresponding earth and ocean system conditions at model year 0. To model sea ice melt, they added a methodical, yet variable freshwater flux from the Arctic into the North Atlantic which was increased linearly through model year 2200. This gradual increase in freshwater flux into the North Atlantic corresponded to a gradual decrease in AMOC strength, consistent with predictions made by the research team. AMOC strength began diminishing in model year 800 and abruptly collapsed in model year 1758. This collapse represented a five-fold decrease in AMOC strength over the course of a century from model years 1750 to 1850, a shockingly abrupt change given the slow, consistent freshwater flux into the North Atlantic. By model year 2000, northward heat transport by the AMOC in the Atlantic decreased to nearly zero.

Figure 2: AMOC strength at 1000m depth and 26° N latitude. Yellow band shows the range of previously observed AMOC strength (Adapted from Van Westen et al., 2024).

Researchers found influential and dynamic changes to physical properties in oceans across the globe with AMOC collapse. Sea surface temperatures (SST) in the Northern Hemisphere after AMOC collapse significantly cooled, with differences as large as 10℃ observed off the coast of western Europe. SSTs increased slightly in the Southern Hemisphere due to the near absence of northward heat transport by the AMOC. Dramatic shifts in salinity in the upper 100 meters of the ocean were observed in addition to the complete interruption of deep ocean convection in the North Atlantic. Sea-level also rose nearly 70 cm in some regions of the coastal Atlantic due to AMOC collapse.

Researchers also investigated potential effects of AMOC collapse on climate and sea-ice extent in both the Northern and Southern Hemispheres. Significant changes to Hadley Cell air circulation and the subtropical jet stream were observed. Sea ice coverage in the Arctic extended to 50°N in the Arctic (current sea ice rarely forms below 60°N), while Antarctic sea-ice retreated. Model outputs showed atmospheric temperature decreases by around 3℃ per decade in the Northern Hemisphere, a rate at which human adaptation efforts would be largely impossible (current rates of temperature increase due to anthropogenic climate warming are ~0.2℃). These temperature shifts were amplified by ice-albedo feedback, where increased ice coverage in the Northern Hemisphere after AMOC collapse reflects a larger amount of solar radiation back into space, reducing atmospheric temperatures further. Additionally, precipitation patterns in tropical regions shifted with a slight increase in atmospheric temperature in the Southern Hemisphere after AMOC tipping. These results explicitly demonstrate that AMOC tipping would have dramatic, cascading climate impacts across the globe.

Van Westen and colleagues’ study was also the first of its kind to develop a comprehensive warning system for AMOC collapse based on historical climate and oceanographic data and model predictions. Observation of freshwater transport at 34°S, an important proxy for AMOC strength, and the identification of a minimum value for freshwater transport at which AMOC collapse could occur are essential characteristics of AMOC tipping that Van Westen and colleagues identified. These markers of AMOC strength provide an observable set of characteristics that could help predict AMOC collapse in real life.

This research is especially unique because it provides a definitive, model-based answer to the question of whether AMOC collapse can occur in climate models. Prior researchers assumed that AMOC tipping was highly theoretical and would not be predicted in a model that accurately accounts for complicated elements of climate systems. Van Westen and colleagues’ findings clearly demonstrate that AMOC tipping is not only possible, but highly likely under sufficient freshwater influx due to melting Arctic ice.

While the simulation performed by Van Westen et al. (2024) represents an effective predictor of major changes in Atlantic circulation, more data is needed to optimize predictive climate models and apply findings to real climate systems. Van Westen’s research team was unable to provide a meaningful estimate of when an actual AMOC tipping event could occur due to uncertainties in the rate and effects of future climate change. In a paper examining crucial climate tipping points, another European research team estimated that AMOC collapse could occur anywhere from 15-300 years from now, with researchers agreeing that collapse may most likely occur 50 years from now (Armstrong et al., 2022). Another study by researchers from the University of Copenhagen predicted with 95% confidence that tipping may occur from 2025-2095 (Ditlevsen & Ditlevsen, 2023). Precise monitoring of the physical changes in the North Atlantic and stringent data collection are essential to develop more accurate predictions of when AMOC collapse could occur in real life.

This research by Van Westen and colleagues shows evidence that the AMOC could reach a tipping point due to freshwater transport, temperature changes, and salinity changes in the Atlantic, leading to catastrophic climate impacts across the globe, especially in the Northern Hemisphere. Predictive models of major climate events are instrumental in helping communicate the severity of anthropogenic climate change and should be utilized by scientists, policymakers, and advocates throughout the transition away from our reliance on high emission fossil fuel combustion.

References:

Armstrong McKay, D. I., Staal, A., Abrams, J. F., Winkelmann, R., Sakschewski, B., Loriani, S., Fetzer, I., Cornell, S. E., Rockström, J., & Lenton, T. M. (2022). Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science, 377(6611), eabn7950. https://doi.org/10.1126/science.abn7950

Caesar, L., McCarthy, G. D., Thornalley, D. J. R., Cahill, N., & Rahmstorf, S. (2021). Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nature Geoscience, 14(3), 118–120. https://doi.org/10.1038/s41561-021-00699-z

Danabasoglu, G., Lamarque, J.-F., Bacmeister, J., Bailey, D. A., DuVivier, A. K., Edwards, J., Emmons, L. K., Fasullo, J., Garcia, R., Gettelman, A., Hannay, C., Holland, M. M., Large, G., Lauritzen, P. H., Lawrence, D. M., Lenaerts, J. T. M., Lindsay, K., Lipscomb, W. H., Mills, M. J., … Strand, W. G. (2020). The Community Earth System Model Version 2 (CESM2). Journal of Advances in Modeling Earth Systems, 12(2), e2019MS001916. https://doi.org/10.1029/2019MS001916

Ditlevsen, P., & Ditlevsen, S. (2023). Warning of a forthcoming collapse of the Atlantic meridional overturning circulation. Nature Communications, 14(1), 4254. https://doi.org/10.1038/s41467-023-39810-w

The Ocean Conveyor—Woods Hole Oceanographic Institution. (n.d.). https://www.whoi.edu/. Retrieved April 21, 2024, from https://www.whoi.edu/knowyourocean/oceantopics/how-the-ocean-works/ocean-circulation/the-ocean-conveyor/

Van Westen, R. M., Kliphuis, M., & Dijkstra, H. A. (2024). Physics-based early warning signal shows that AMOC is on tipping course. Science Advances, 10(6), eadk1189. https://doi.org/10.1126/sciadv.adk1189