Climate variability and life history impact stress, thyroid, and immune markers in California sea lions (Zalophus californianus) during El Niño conditions

By Isabelle Geller, SRC intern

There are many situations which may increase the level of stress in an animal – for example, not being able to eat enough food to meet energy demands or being in temperatures above or below a tolerable range they can. DeRango et al. (2019) aimed to study both of these factors with respect stress levels of California sea lions (CSL) (Figure 1). Specifically, the authors looked at impacts of environmental change (e.g. variability over the course of the study) and life history (e.g. pre-breeding and post-breeding stages – juvenile and adult – with different energy demands) on CSL during the El Niño of 2015-2016.

Figure 1: California Sea Lion (Rhododendrites [CC BY-SA 4.0 (]).

El Niño conditions are categorized by unusually warm and nutrient poor waters, typically in the Pacific region. DeRango and colleagues postulated that such unsuitable weather could change CSL hunting patterns, likely by pushing them further from shore resulting in larger energetic costs from the CSL. Likewise, for the adult male CSL during peak breeding season they would cease hunting to concentrate on the arduous breeding tenure.

To conduct the study, blood samples were taken from juvenile and adult CSL during October 2015/ October 2016 and March 2016/ August 2016 respectively (Figure 2). From the blood samples they analyzed stress hormones, glucose levels, thyroid hormones, immune markers and interactions between the HPA (hypothalamus, pituitary gland, and adrenals glands) axis; which they hypothesized would all be suppressed. However, the results were a bit different from expected:

  1. From 2015 to 2016 the glucose and stress hormone levels for juvenile and adult male CSL decreased.
  2. From 2015 to 2016 the thyroid hormones for juvenile and adult male CSL increased
  3. From 2015 to 2016 immunoglobin increased in juveniles but decreased for adult male CSL after breeding.

Figure 2: Timeline of events for the research of CSL. Types of CSL sampled: JUV = Juvenile, Ad M = Adult Male. Locations where CSL were sampled: ANI = Año Nuevo Island, California and Astoria, Oregon. (DeRango et al. 2019)

So, what do the results mean? The authors interpreted these trends as follows:

  1. From 2015 to 2016 the glucose and stress hormone levels for juvenile and adult male CSL decreased:

Since the juvenile sea lions had been facing chronic stress due to lack of food and the adult male sea lion due to sustained breeding period, they animals may have been unable to mount a normal stress response to the handling and drawing of blood. Additionally, due to a lack of nutrients for juvenile seals and the extremely energetically expensive reproductive process glucose (an important energy in organisms) decreased.

2. From 2015 to 2016 the thyroid hormones for juvenile and adult male CSL increased

To support energy intensive activities like hunting and breeding, thyroid function to increase during stressful activities like breeding and foraging. This may occur since the CLS were fasting, for aforementioned reasons, thus the stress hormone may not have had the same impact of suppression on the thyroid hormone as usual.

3. From 2015 to 2016 immunoglobin increased in juveniles but decreased for adult male CSL after breeding.

Immunoglobin, which is a markers for immune system cells, increased in juveniles likely due to greater exposure to pathogens, which would increase during El Niño events. However, immunoglobin decreased for adult male CSL, because reproduction and energetic limitations caused immunosuppression.

Looking to the future, this study has shown the impact of climate change on life history events and on the CSL population – this has contributed to an understanding of the marine mammal stress response to capture, and could help to create better research protocol for the CSL in the future.

Works cited

DeRango EJ, Prager KC, Greig DJ, et al (2019) Climate variability and life history impact stress, thyroid, and immune markers in California sea lions (Zalophus californianus) during El Niño conditions. Conserv Physiol 7:1–15. doi: 10.1093/conphys/coz010

Northward range expansion in spring-staging barnacle geese is a response to climate change and population growth, mediated by individual experience

By Gaitlyn Malone, SRC Masters Student

As climate change continues to rapidly alter environments, it is important to investigate how these changes impact the species that utilize these areas. When faced with these alterations, organisms will often have to adjust their behaviors in order to increase their survival. Animals that migrate long distances in order to meet their fitness needs are a great example of species that will often have to modify their behavior since they depend on different environments that are often far apart from one another and may change at varying rates. However, the means by which these organisms adjust can differ and there is very little knowledge about how many of these responses come about.

Figure 1: Barnacle Goose (Source: Dr. Raju Kasambe, Wikimedia Commons)

A recent study investigated how an increasing population of barnacle geese (Branta leucopsis) responded to the environmental changes occurring within their two spring-staging areas located in Helgeland and Vesterålen, Norway (Tombre et al. 2019). The southernmost staging area, located in Helgeland, had been traditionally used by the barnacle geese, however since the mid-1990s, an increasing number of geese had started to stage in Vesterålen, located 250 km north of Helgeland. From 1975 until 2017, the authors collected information on goose population numbers as well as weather conditions in order to determine the extent to which these characteristics contributed to the alteration in staging area use by both new recruits in the population and older individuals that altered their migratory strategy at a later stage in life. To determine whether climate change was a contributing factor to the diversity in population distribution, the authors estimated foraging conditions at both locations to see if differences in food conditions as well as increasing competition over resources due to population growth led to the change in staging area use.

Figure 2: Spring migrations routes and staging areas of barnacle geese (Source: Tombre et al. 2019)

Through their work, it was determined that while there was enhanced grass growth in Helgeland, the condition of foraging materials remained stable over time. However, in Vesterålen production of digestible materials increased, leading the authors to believe that the changing conditions in this area contributed to the change in the barnacle geese’s range. Additionally, it was determined that the population growth at Vesterålen occurred through to two different processes. First, during the initial years of colonization and after, young geese tended to switch to Vesterålen first and comprised the highest numbers within the flock. Secondly, it was also found that while older birds had a decreased probability of switching from Helgeland to Vesterålen, over time the probability increased for all ages. These findings suggest that barnacle geese use both social learning and individual experiences to adjust in their behavior and respond rapidly to climate change. These results are one of the first to portray the role that individual decisions play in population scale patterns and add to the growing knowledge on the importance of social learning in the development of migratory behaviors.

Works cited:

Tombre IM, Oudman T, Shimmings P, Griffin L (2019) Northward range expansion in spring ‐ staging barnacle geese is a response to climate change and population growth , mediated by individual experience. 1–14. doi: 10.1111/gcb.14793

A microscopic organism with a macroscopic impact: How climate change is affecting harmful algal blooms and what this means for future generations

By Carolyn Hamman, SRC intern

Phytoplankton are photosynthetic microorganisms that exist in both marine and freshwater environments. There are several different types of phytoplankton each with their own unique preferred environmental parameters and strategies for growth. For example, some phytoplankton (called coccolithophores) use calcium to create protective plates they use as a defense mechanism (Beaufort et al. 2011). Phytoplankton are a vital component in aquatic ecosystems as they are responsible for the majority of primary productivity that occurs. In fact, phytoplankton have been considered a driver in climate as 30% of anthropogenic carbon emissions have been absorbed by the ocean and over 90% of the heat increase the Earth has seen the ocean has taken up (Hallegraeff 2010). While phytoplankton plays a vital role in many processes in the ocean, there are also occurrences of harmful algal blooms (HABs). HABs are phenomena that have been a natural process throughout history (Hallegraeff 2010). These blooms can be harmful for two reasons. Certain species of phytoplankton can produce different types of neurotoxins that have been known to cause different problems such as respiratory issues (such as with the Florida Red Tides) or gastrointestinal and neurological illnesses. HABs don’t have to necessarily produce toxins to be considered harmful. The dense covering that algal blooms can cause blocks UV light from reaching certain depths of the ocean. The high amount of phytoplankton will cause a depletion in nutrients that can disrupt other ecosystems who rely on the nutrients as well. Once the phytoplankton finally use up the nutrients, they die in massive amounts that deplete the oxygen in the water and causes massive anoxia (Hallegraeff 2010).

Climate refers to the large-scale changes that occur in the atmosphere, hydrosphere, and cryosphere (Hallegraeff 2010). There are natural fluctuations in the climate that have caused periods of warming or cooling. However, since around the Industrial Revolution, the CO2 levels have increased from 280 to >380 ppm, and there have been temperature increases in the past 40 years that are at a rate far faster than ever seen before (Hallegraeff 2010). Phytoplankton have short generation times and longevity, which means they can respond quickly to climate change. This is true for HABs as well. Though phytoplankton species can evolve and change, the changing environmental parameters will favor species with certain parameters. As climate continues to change, it is imperative to understand how HAB will respond. The issue is that there are numerous amounts of factors that all play a role in determining which species of algae bloom (Zingone & Enevoldsen 2000). These stressors caused by climate change can include increased temperature, enhanced surface stratification, alteration of ocean currents, intensification or weakening of nutrient upwelling, stimulation of photosynthesis by elevated CO2, reduced calcification from ocean acidification, and changes in land runoff and micronutrients (Hallegraeff 2010). Each of these parameters can be analyzed to determine how HAB will respond to climate change. In the past 30 years, there has been an increase in frequency and intensity of HAB as well as how widespread they are (Hallegraeff 2010).

As greenhouse gas concentrations have increased there has been an increase in surface temperature, lower pH, and changes in vertical mixing, upwelling, precipitation, and evaporation patterns (Moore et. al. 2008). As current strength and number of blooms have increased, the range of HAB has expanded (Hallegraeff 2010). Areas that had previously not seen HAB have noticed a significant increase in the past decade. HAB rely on temperature to bloom, and with an increase in overall temperature blooms have started to occur earlier than what has previously been observed (Hallegraeff 2010). Phytoplankton living in shallower areas will also be more effected by temperature than phytoplankton in open oceans (Hallegraeff 2010). This means that HAB closer to the shore will undergo larger changes than the populations in the open ocean. With increased greenhouse gases comes increase in sea-level, wind, and mixed-layer depth, which has an impact on the number of upwelling and downwelling events and thus concentrations of macronutrients (Hallegraeff 2010). The change in wind will also influence transport of nutrients by air (known as aeolian transport). The net result is a decrease in mixing depth at higher latitudes, which results in higher phytoplankton biomass (Hallegraeff 2010). A noticeable change in precipitation is occurring due to climate change as well, where there are now periods of concentrated rainfall followed by long dry spells. This change is causing certain dinoflagellates (a type of phytoplankton) to bloom in higher concentrations than previously seen before (Hallegraeff 2010).

A schematic showing how climate warming affects mixing in low and high latitudes. The differences in mixing results in differences in HAB (Hallegraeff 2010)

The environmental changes caused from climate change has caused HAB patterns not previously seen before. Going in to the future, the species-specific responses to these parameters can be used to better predict where HAB will occur and the concentration they could occur at. The potential issue with such predictions is that it is exceedingly difficult to be able to predict how several environmental parameters working together will cause phytoplankton to respond. It is recommended that there be a more improved global ocean observation system that can monitor all of these parameters simultaneously (Hallegraeff 2010). As previously mentioned, there could be increased adverse effects on human health due to increased HAB, but very little has been done to study how humans respond to different phytoplankton toxins (Moore et. al. 2008). More research is needed to evaluate associations between human health and HAB to better respond when harmful algal bloom occurrence continues to increase in to the future.

A graph showing the relationship between the number of algal blooms and human population over time. Populations and boom frequency have both increased over time (Zingone & Enevoldsen 2000)

Works cited

Beaufort, L., Probert, I., De Garidel-Thoron, T., Bendif, E. M., Ruiz-Pino, D., Metzl, N., … & Rost, B. (2011). Sensitivity of coccolithophores to carbonate chemistry and ocean acidification. Nature476(7358), 80.

Hallegraeff, G. M. (2010). Ocean Climate Change, Phytoplankton Community Responses, And Harmful Algal Blooms: A Formidable Predictive Challenge. Journal of Phycology, 46(2), 220-235. doi:10.1111/j.1529-8817.2010.00815.x

Moore, S. K., Trainer, V. L., Mantua, N. J., Parker, M. S., Laws, E. A., Backer, L. C., & Fleming, L. E. (2008). Impacts of climate variability and future climate change on harmful algal blooms and human health. Environmental Health, 7(S4), 1-12. doi:10.1186/1476-069x-7-s2-s4

Zingone, A., & Enevoldsen, H. O. (2000). The diversity of harmful algal blooms: A challenge for science and management. Ocean & Coastal Management, 43(8-9), 725-748. doi:10.1016/s0964-5691(00)00056-9

Climate Change Induced Trophic Amplification Declines Planktonic Biomass

By: Delaney Reynolds, SRC Intern

Figure 1: A collage of different planktonic organisms (Source:

Plankton, including phytoplankton and zooplankton, make up 99% of all marine life and form the base of the food web. Phytoplankton undergo photosynthesis, much like plants do, and thus their growth and population size are dependent on availability of nutrients and levels of light. Zooplankton feed upon phytoplankton and thus their population size is partly dependent on phytoplankton populations.

The effects of anthropogenic climate change on phytoplankton and zooplankton populations is widely unknown, but scientists are taking steps to determine what those effects may be.

In a study by the Dynamic Meteorology Laboratory in France, Dr. Lester Kwiatowski took a look at how the trophic amplification of plankton biomass changes based on different models of future climate change, as well as how an amplification of this response may trickle through the food web.

Two different modeling techniques were used in this study: the Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth System Models and the Pelagic Interactions Scheme for Carbon and Ecosystem Studies Quota (PISCES-QUOTA) model. The CMIP5 models modeled the trophic interactions between zooplankton and phytoplankton biomass under twenty-first century climate change projections. The PISCES-QUOTA model was used to explore what the mechanisms controlling zooplankton and phytoplankton trophic interactions might be under different climatic conditions.

Figure 2: This figure displays the projected percentage of plankton biomass anomaly by year from 1850 to 2100, as well as according to latitude. All three populations of plankton (phytoplankton, microzooplankton, and mesozooplankton) decrease in biomass; however, it can be concluded that the zooplankton will be much more negatively affected than the phytoplankton. It can also be deduced that in the lower latitudes, where it is warmer, zooplankton will also be more negatively affected than phytoplankton (Lester et al. 2018).

Kwiatowski found that both models projected a decline in both in zooplankton biomass and phytoplankton biomass as a result of climate change, with a moderately larger decrease in zooplankton biomass than phytoplankton biomass. According to the CMIP5 models, phytoplankton biomass is expected to decline by 6.1 ± 2.5% and zooplankton biomass is expected to decline by 13.6 ± 3.0%. The PISCES-QUOTA model split up zooplankton into two groups: microzooplankton and mesozooplankton. This model found that phytoplankton biomass is expected to decline by 8.5%, microzooplankton biomass by 15.4%, and mesozooplankton biomass by 20.6%. Here again, a slightly greater decrease in zooplankton biomass can be found than phytoplankton biomass. The PISCES-QUOTA model also determined that the driving factor affecting the biomass levels was primarily the fact that “primary production decreases in equatorial and subtropical biomes due to stratification-driven reductions in nutrient availability” (Kwiatowski et al., 2018).

Looking at comparisons between carbon, nitrogen, and phosphorous stoichiometry, the discrepancy between phytoplankton and zooplankton can be explained. As a result of climate change, the PISCES-QUOTA model also predicted a decrease in the phytoplankton nitrogen content by 1.1% and phosphorous content by 6.4%, just in the twenty-first century. As zooplankton consume phytoplankton, this decrease of nitrogen and phosphorous in phytoplankton will ultimately lead to a decline in the growth efficiency of zooplankton and a decrease in the overall zooplankton population.

Phytoplankton and zooplankton comprise of the base of the marine food web and also produce about 50% of the earth’s oxygen. Without them, many larger organisms would be heavily impacted. Studies just like this one can help us better understand the future that our delicate food web may face under the threats of climate change and give us insight into how we might be able to combat the probable effects.

Works Cited

Kwiatkowski, L., Aumont, O., & Bopp, L. (2019). Consistent trophic amplification of marine biomass declines under climate change. Global change biology25(1), 218-229.

Investigating the vulnerability of European Seafood Production to Climate Warming

By: Gaitlyn Malone, SRC Intern

As the world’s climate continues to change, economic, social, and environmental changes will undoubtedly occur along with it. One sector that is expected to be economically affected by climate warming is seafood production (Breitburg et al., 2018). Seafood production, which includes both farmed and captured fish, shellfish, and seaweed in marine and freshwater, will experience changes since the warming of an environment has the ability to change both a species’ distribution and life history characteristics (Pecl et al., 2017; Cochrane et al., 2009). Therefore, it is crucial to work towards being able to predict and understand the extent of these changes in order to prepare for the future.

A recent study (Blanchet et al., 2019) examined the effects of climate change on seafood production within each European country in order to identify potential challenges and opportunities within the sectors of marine fisheries, marine aquaculture, and freshwater production. To do so, the researchers combined information on the target species’ temperature preferences, life history characteristics, and production volume to determine their biological sensitivity (BS) and the maximum temperature (Tmax) that they were experiencing. They then determined the adaptive ability of seafood production in each country or sector by determining the number of species that the country/sector exploits and those species’ temperature ranges. A country or sector that exploits a higher number of species will be more likely to adapt in response to climate change. A species with a wide temperature range would also potentially be more adaptable since they are able to withstand a variety of temperatures.

Figure 1: Biological sensitivity index versus the temperature range of each species within the sectors of a) marine fisheries, b) marine aquaculture, and c) freshwater production. The size of the bubbles relates to the total volume produced for each particular species in that sector (Blanchet et al., 2019).

Figure 2: Ranking of each European country’s vulnerability to warming based on their weighted temperature sensitivity and weighted biological sensitivity for each of the three production sectors. The size of the bubbles represents the relative contribution of each country to the total European production volume within that sector (Blanchet et al., 2019).

Overall, seafood production was found to generally be more vulnerable within the marine fisheries and aquaculture sectors. The freshwater sector varied greatly based on country. Within the marine sector, northern countries tended to be more sensitive to warming than southern countries since seafood production in these areas are more dependent on cold-water species with a high BS. Southern countries tended to rely on warmer water species that had a lower BS. The main challenge facing these marine fisheries is due to changes in species distribution. In response to warming, there has been a northward expansion of the range of several species, which in some cases has included a contraction of their southern range. This change in distribution has the ability to affect local fisheries and management, who in southern areas may lose access to their resources, while northern areas may benefit. Aquaculture taking place in temperate zones was also predicted to be at risk from warming conditions, since increasing temperatures have the ability to reduce oxygen levels in the water and increase the metabolic costs for organisms. Disease is also likely to increase in these systems since pathogens may spread more readily. The low amount of species diversity in aquaculture also makes it particularly susceptible to rising temperatures.

Under warming conditions is not impossible to continue producing sustainable seafood, however efforts must be made to adapt to climate change. Therefore, the authors suggest that there must be communication between stakeholders, diversification of exploited species, and transnational cooperation in order to meet these goals.

Work Cited

Blanchet, M.-A., Primicerio, R., Smalas, A., Arias-Hansen, J., Aschan, M. 2019. How vulnerable is the European seafood production to climate warming?. Fisheries Research 209, 251-258.

Breitburg, D., Levin, L.A., Oschlies, A., Gr.goire, M., Chavez, F.P., Conley, D.J., Gar.on, V., et al., 2018. Declining oxygen in the Global Ocean and coastal waters. Science 359 (6371).

Cochrane, K., Young, D.C., Soto, D., Bahri, T., 2009. Climate change implications for fisheries and aquaculture: overview of current scientific knowledge. FAO Fisheries and Aquaculture Technical Paper 530, 212.

 Pecl, G.T.,, M.B., Bell, J.D., Blanchard, J., Bonebrake, T.C., Chen, I.-C., Clark, T.D., et al., 2017. Biodiversity redistribution under climate change: impacts on ecosystems and human well-being. Science 355.



Harmful Algal Blooms and Climate Change: Exploring Future Distribution Changes

By: Chris Schenker, SRC Intern

Across the globe, the effects of climate change are manifesting. Due to anthropogenically-induced environmental changes, the geographic occurrence of many species is being altered, and algae is no exception. Under the right environmental conditions, some algal species can cause harmful algal blooms (HABs) which create toxins and produce many harmful side effects. Fisheries are affected by HABs, as are some filter feeding species. Many commercially important bivalves, such as shellfish, retain these harmful chemicals in their tissue for up to six months. This means that one prolonged algal bloom can close coastal aquaculture and fisheries for months at a time, creating negative economic impacts and posing a threat to public health. Vulnerable species and ecosystems are also sensitive to HABs, and one bad event can push a species to extinction or make long lasting ecosystem-wide changes.

Figure 1: Many commercially important species of shellfish are under threat due to harmful algal blooms. (Source:

Worldwide, blooms have increased in frequency and impact. Different algal species are affected in different ways by environmental conditions, but it is possible that manmade changes have played a part in this. Many HABs that used to only occur at lower latitudes have crept north in recent years, and in this paper, Townhill et al. (2018) aimed to use species distribution modeling to provide a broad overview for “changing geographic affinity” (p. 1884). Using a high-resolution climate model integrated into global climate model outputs, the authors were able to incorporate a species’ global environmental exposure into its habitat suitability function. The “habitat suitability function” was constructed from data on species occurrence for a number of algal species, with an emphasis placed on variables most believed to affect algal occurrence, such as near bottom and sea surface temperature and salinity, differences between the surface and bottom values for each, and bathymetry. Next, a “relative habitat suitability” score between 0 and 1 was generated by running the data through the Maximum Entropy (Maxent) model which describes hydrographic and bathymetry conditions that a species currently seems to favor. Finally, the model was used to generate predictions of the latitudinal center of a species’ distribution in the near-term (2040-2069) and long-term (2069-2098). The estimates were used to understand how a species general distribution may change from the present.

Figure 2: All species studied are expected to experience a global shift towards the poles. (Townhill et al., 2018)

Every species studied was projected to experience a northward global shift, with most of the change occurring at end of the century. Bathymetry and near bed temperature were found to be the variables with the greatest contribution to model fit. All but three species experienced a northward shift in the Northern European shelf seas, with D. acuta and Gymnodinium catenatum having the greatest at 800-1000 km northwards for mid and end of century. G. catenatum was also predicted to have the largest northwards shift globally with an estimate of more than 700 km.

Figure 3: Alexandrium minutum is predicted to have a southward shift in shelf seas, while the other three species shown are expected to have the greatest northward shift. (Townhill et al., 2018)

Although there are differences in species-specific predictions compared to other studies, the work of Townhill et al. (2018) highlights the need for near- and long-term forecasting to understand the risk of future algal species redistribution. More sophisticated future models will likely lead to better predictions, allowing researchers to stay abreast of ecological trends. However, it is also important to understand that relative suitability helps us understand which species might become more prevalent and therefore need closer monitoring, but it is impossible to predict blooms based on abundance data alone. For that, local and near-term environmental conditions are much more important. Thus, this brand of species distribution modeling is meant to supplement conventional monitoring efforts, not replace them.

Work Cited:

Townhill, B. L., Tinker, J., Jones, M., Pitois, S., Creach, V., Simpson, S. D., Dye, S., Bear, E., and Pinnegar, J. K. Harmful algal blooms and climate change: exploring future distribution changes. ICES Journal of Marine Science, 75: 18821893.

Fading Corals: The Effect of Anthropogenic Climate Change on Coral Reefs

By Konnor Payne, SRC intern

Due to the dramatic ecological changes caused by humans to the Earth, a new period has been named after humans called the Anthropocene. In the Anthropocene, it appears, the next change is to the Earth’s coral reefs. The number one cause of stony coral (Reef-building coral) loss is the warming of waters due to anthropogenic global warming (Causey, 2001; Manzello, 2015). As technology and industry continue to accelerate, the issue of global warming will only worsen and thus the coral reefs shall continue to suffer.

Figure 1. The coral is bleached and has had its zooxanthellae expelled. This can occur to any reef-building coral that is under too much stress from outside influences. The coral is starving without the photosynthetic symbiote and is likely to starve to death. (Source: “KeppelBleaching.”, 22 Aug. 2011,

Corals are tiny soft-bodied organisms related to sea anemones that build a calcium carbonate skeleton around themselves. Within their bodies is a symbiotic dinoflagellate, called zooxanthellae, that photosynthesizes to provide the corals with organic matter. Bleaching is when a coral colony becomes so overly stressed that the zooxanthellae are expelled resulting in a lack of color. In this bleached state, the coral begins to starve and is likely to die. In the Florida Keys Reef Tract (FKRT) increasing sea surface temperature has led to an increase in the number of major bleaching events (Van Hooidonk et al., 2013), leading to the loss of 40% of stony corals since 1996 causing an ecological shift towards octocorals, macroalgae and sponges (Ruzicka et al., 2013).

In May of 2015 and 2016, researchers excavated coral skeletal cores from the two most critical reef-building corals, Siderastrea sidereal and Pseudodiploria strigose, in the FKRT to examine skeletal density, growth and calcification rates. Using X-rays and a 3D modeling program, (Horos V2.0.2) the layers of coral grown each year could be analyzed accurately pixel by pixel. The researchers found that the skeletal density remained consistent up until the last century, in which overall skeletal density significantly decreased, but extension and calcification rates did not change significantly compared to their respective biological history (Rippe, 2018). Both species of coral have been able to sustain baseline growth rates despite recent bleaching events and chronic ocean warming. This suggests that corals of the subtropical environment are likely to have a buffer to the effects of ocean warming and the underlying cause of reduction in the skeletal density is levels of aragonite saturation in the water (Rippe, 2018). The study suggests that further research into the carbonate chemistry of the FKRT is required to understand how heavily aragonite saturation affects skeletal density.

Figure 2. The coral skeletal core has distinctive bands to distinguish skeletal density, extension and calcification rates over the years. By comparing past to future bands, the anthropogenic effects on the coral can be visually determined. (Source: Felis 2005).

Works Cited

Causey, B. (2001). Lessons learned from the intensification of coral bleaching from 1980–2000
in the Florida Keys, USA. Paper presented at the Proceedings of the Workshop on Mitigating Coral Bleaching Impact through MPA Design. Honolulu, Hawaii.

Felis, Thomas. “Paleoclimatology: Climate Close-Up.” NASA Earth Observatory, 23 Dec. 2005,
Manzello, D. P. (2015). Rapid recent warming of coral reefs in the Florida Keys.
Scientific Reports, 5.

Rippe, John. (2018). Corals sustain growth but not skeletal desnity across the Florida Keys Reef
Tract despite ongoing warming. Primary Research Articles.

Ruzicka, R., Colella, M., Porter, J., Morrison, J., Kidney, J., Brinkhuis, V., … Meyers, M.
(2013). Temporal changes in benthic assemblages on Florida Keys reefs 11 years after the 1997/1998 El Niño. Marine Ecology Progress Series, 489, 125-141.

Van Hooidonk, R., Maynard, J., & Planes, S. (2013). Temporary refugia for coral reefs in a
warming world. Nature Climate Change, 3(5), 508-511.

Gravity of human impacts mediates coral reef conservation gains

By Brenna Bales, SRC intern

Communities around the world depend on coral reefs for their livelihood, for tourism, and for protection against coastal degradation. With an increasing human population comes increasing human impact on these coral reefs and a decrease in the ability of a reef to provide the benefits listed above. Direct human impacts include overfishing, polluting the reef with trash or chemicals, and dredging; however, there are indirect human impacts such as anthropogenic climate change. Greenhouse warming affects ocean temperature which can stress corals (Jokiel 2004), and ocean acidification from carbon uptake can decrease the ability of corals to build limestone foundations (Langdon et al, 2000).

In Cinner et al’s analysis, the magnitude of human impact on of 1,798 tropical reefs in 41 nations/states/territories was described and quantified. In order to quantify this impact, the authors used a social science metric termed “gravity”, which has been used from economics to geography. For the adaptation to an ecological analysis, the gravity of human impact was measured as a function of how large and how far away a population of humans was to a certain coral reef (Figure 1). In each location, the status of reef management ranged from openly fished (little to no management), to highly protected marine reserves where fishing is completely prohibited.

Figure 1. The authors’ interpretation of “gravity” as a function of the population of an area
divided by the time it takes to travel to the reefs squared. (Cinner et al, 2018)

Two expected “conservation gains” (differences in the progress of a coral reef ecosystem when protected versus unprotected) in all regions were analyzed as to how they are influenced by human activity. The first was targeted reef fish biomass (species usually caught in fisheries) and the second was the presence of top predators within the ecosystem. Conservation gains can be beneficial to both people and ecosystems; When the health of a protected coral reef improves, it might drive new recruits and help re-establish other nearby reefs that are fished more. The authors hypothesized that the target conservation gains would decline with increasing gravity in areas where fishing was allowed, but that marine reserves would be less susceptible to these gravity influences.

Analysis of visual fish count data collected from 2004-2013 showed that gravity strongly predicted the outcomes for fish biomass in a reef ecosystem. Biomass in marine reserves showed a less steep decline with increasing impact as compared to openly fished and restricted areas (Figure 2). This was due to an unforeseen relationship between gravity and the age of a marine reserve. In high-gravity areas, older reserves contributed more to fish biomass when compared to low-gravity areas. These older reserves have had more time to recover after periods of high fishing stress. Even in the highest-gravity reserves, fish biomass was about 5 times higher than in openly fished areas. Top predators were only encountered in 28% of the reef sites, and as gravity increased, the chance of encountering a top predator dropped to almost zero. Overall, highly regulated marine reserves in low-gravity situations showed the highest biomass levels, and the greatest chance of encountering a top predator.

Figure 2. Modeled relationships showing reef fish biomass declines with gravity increases by
regulation type. Openly fished (red), restricted (green), and high-compliance marine reserves
(blue). (Cinner et al, 2018)

Four explanations for the decrease of fish biomass and top predator encounters were (i) human impact in the surrounding area of a marine reserve affecting the interior, (ii) poaching effects, (iii) life history traits of top predators making them susceptible to even minimal fishing stress, and (iv) high-gravity reserves being too young or too small for drastic improvement. The fourth explanation was further analyzed, where large versus small reserves were compared. Not surprisingly, larger reserves had higher biomass levels and top predator encounter probabilities. Lastly, the ages of the reserves were examined. The average reserve age was 15.5 years compared to older reserves (29 +/- years), and older reserves had a 66% predicted increase in biomass levels. Analysis of the likelihood of encountering a top predator was less definitive, suggesting high-density areas, no matter the age, reduce this probability greatly.

Ecological trade-offs such as high-gravity reserves being beneficial for conservation gains like reef fish biomass, but not so much for top predators, are important to consider. Top predators can face more fishing stress even in remote areas due to their high price in international markets, such as sharks for their fins, explaining the observed difference in low-gravity fished areas versus low-gravity marine reserves. Overall, when aiming to create an effective marine reserve or even regulations that aid in conservation gains, it is imperative to consider the gravity of human impact in the surrounding areas. How the impacts of gravity can be reduced is critical as populations grow along coastlines and climate change stressors increase as well. Multiple forms of management will most likely provide the most benefit to stakeholders (Figure 3) and the ecosystem.

Figure 3. A fisherman in the town of Paje, Tanzania takes his boat out behind the reef barrier to
catch a meal. Stakeholders are an important part in considering reef management decisions, as
millions of people rely on the reefs for their meals just as this fisherman.

Works Cited

Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., Goddard, J., Marubini, F., Aceves, H., Barnett, H. and Atkinson, M.J., 2000. Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef. Global Biogeochemical Cycles, 14(2), pp.639-654.

Jokiel, P.L., 2004. Temperature stress and coral bleaching. In Coral health and disease (pp. 401-425). Springer, Berlin, Heidelberg.

“Climate-driven range shifts of the king penguin in a fragmented ecosystem”: a summary of the effects of anthropogenic climate change on habitat fragmentation through genomic analysis in the king penguin community

By Julia Saltzman, SRC intern

Climate change is a hot topic today, not only in the world of science, but also in the world of politics and policy (Figure 1). Despite this fact, it has not been until recently that scientists have started to study the impacts of climate change on specific species. Because anthropogenic climate change is known to have important consequence across biologic communities, having and understanding of the nature and extent of species’ responses is crucial in modeling policy for effective environmental change (Cristofori Et. Al., 245). In the article, Climate-driven range shifts of the king penguin in a fragmented ecosystem, research is discussed which focuses on the upper-level predator, the king penguin, in one of the most rapidly changing ecosystems on the planet: the sub-Ant-arctic region.


Figure 1: global surface temperature in 2017 compared to the 1981-2010 average. High latitudes of the Northern Hemisphere were especially warm, though temperatures across most of the planet were warmer than average (red colors). (Source: NOAA map, based on data from NOAA NCEI.)


The king penguin exhibits high levels of dispersal, and fragmented distribution. It has been suggested that the remarkably high migration rate among colonies can explain this. In order to test this hypothesis, researchers produced a genome-wide data set (Cristofori Et. Al., 246). including about 35,000 independent polymorphic loci genotyped in 163 individuals from 13 different locations covering most of the king penguin (Figure 2). Following the data collection, it was verified that the long-term relationship between paleohabitat reconstruction and the species’ past demography can be inferred from genomic data. Based upon this paleogenetic reconstruction, which allowed or analysis of location specific genomes, found that heterogeneous environmental changes lead to uncoupled effects on different crucial areas of the king penguins’ habitat.


Figure 2: the king penguin, Aptenodytes patagonicus, at first glance appears to be very similar to the emperor penguin, however, it is smaller and completely different genetically. (Source: Wikipedia commons).


Although this data gives highly complex insight into the genomic of the king penguin community across boundaries of fragmentation, it can tell scientists and policy makers really good information about the near-future scenarios which can project changes in these penguins’ range and population size. Although some scientists may suggest that the species can evolve overtime to adapt to anthropogenic climate change (figure 3), species fragmentation, and changes in resource partitioning, past data has found that due to the king penguins’ low genetic diversity and long generation time, the species is not expected to undergo any rapid adaptive evolution to new conditions in its range. Because species fragmentation and climate change go hand in hand, not only in the king penguins’ population, but in the overall ecosystem of the earth, this data collection methodology and results can give insight into the effect of habitat fragmentation on species’ niche and genetic diversity. This data can be used collaboratively to help mitigate the effect of anthropogenic fragmentation which happens so frequently in a plethora of ecological niches.


Figure 3: From a study of detailed analysis of a recently published Antarctic temperature reconstruction, which combined satellite and ground information using a regularized expectation–maximization algorithm (O’Donnell et al. 2009).


Works Cited:

O’Donnell, R., Lewis, N., Mcintyre, S., & Condon, J. (2011). Improved methods for PCA-based reconstructions: Case study using the Steig et al. (2009) antarctic temperature reconstruction. Journal of Climate. doi:10.1175/2010JCLI3656.1

Climate Change: Global Temperature | NOAA, 1 Aug. 2018,

Weintraub, Karen. “Largest King Penguin Colony in the World Drops by 90%.” The New York Times, The New York Times, 31 July 2018,

Cristofari, R., Liu, X., Bonadonna, F., Cherel, Y., Pistorius, P., Le Maho, Y., … Trucchi, E. (2018). Climate-driven range shifts of the king penguin in a fragmented ecosystem. Nature Climate Change. doi:10.1038/s41558-018-0084-2

Climate Change and Fish Performance: How can aquatic acidification affect oxygen transport and swim performance?

By Luisa Gil Diaz, SRC intern

Climate change is becoming an ever-more pressing concern. The concentration of atmospheric carbon dioxide (CO2) has rapidly increased to about 400 ppm in 2015; this is the highest it’s been 800,000 years (Luthi et al., 2008). When we think about the effects these high concentrations have on our earth’s systems, we might only consider the atmosphere and weather patterns. However, it is important to remember that the ocean is the largest carbon sink on earth. We are already starting to see the effects of increased carbon dioxide concentrations, as well as increased partial pressure coming from CO2, in the form of ocean acidification and coral bleaching. However, not much information has been gathered on the effect of increased partial pressure from carbon dioxide (PCO2) on fish metabolic performance, which is an important benchmark of their ability to survive.

Increasing levels of atmospheric CO2 have led to changes in ocean pH (Plumbago AnnualpHChange. Digital image. Wikimedia. N.p., Apr. 2009. Web. 23 Mar. 2018).

Kelly D. Hannan and Jodie L. Rummer’s study is a meta-analysis of the work that has been done on this subject. Data analyzed included both saltwater and freshwater environments. However, it is difficult to predict how rising CO2 concentrations will affect freshwater systems due to their high variability. Overall, it is predicted that increasing CO2 concentrations will affect the calcification rates, growth, reproduction, and immune functioning of organisms. It has been observed that marine and freshwater fish can physiological compensate for extremely high levels of ocean acidification, but behavioral defects have also been observed. Therefore, “these behavioral impairments demonstrate that despite fish being efficient acid-base regulators, they may not be as tolerant to acidosis as previously predicted” (Hannan and Rummer 2018). Acid-base regulation requires energy and can be metabolically taxing. The delivery of oxygen (O2) to tissues can result in maintained or increased aerobic scope across a wide range of teloest species (aerobic scope refers to the total aerobic energy available to an organism above basic maintenance costs for basic life-history processes and can be used as a measure of health). The goal of Hannan and Rummer’s meta-analysis was to see what other mechanisms were used by both freshwater and saltwater fish to combat the effect of increased CO2.

Teleosts are bony fish (Viswhapraba. Puntius Sarana. Digital image. Wikimedia. N.p., Sept. 2011. Web. 23 Mar. 2018).

To begin this meta-analysis, search engines such as Google scholar were used to look up studies using key words such as “teleost”, “Oxygen consumption”, “aerobic scope”, “ocean acidification”, and “Carbon dioxide”. From the results that the search engines generated, all studies that investigated the effect of elevated PCO2 on oxygen uptake in fishes were reviewed. The researchers analyzed the pH range, PCO2 range, the species assessed, the life stage, the length of PCO2 exposure, the ecosystem, and the type of response from each one of the papers to find trends and commonalities. Of the 26 instances where responses to elevated PCO2 , the majority (73.1%) reported no effect on Aerobic scope. 15.3% reported a decrease in aerobic scope and 11.5% reported an increase. These results reinforce the idea that fish are efficient regulators and can withstand pressure from differing pH conditions in their environments. However, it is important to note that the majority of the species analyzed were adult teleosts (bony fish). Furthermore, because the meta-analysis looked at different studies which used different methods, there are gaps in data that make it impossible to get a whole-picture analysis of animal performance and fitness. This lack of holistic information will make it difficult to draw predictions on how fish populations will be affected by ocean acidification in the long term. The majority of animals studied where teleosts, who are known to benefit from the Root effect. Yet, in the elasmobranchs that were included there still seemed to be resistance to changes in Aerobic scope in response to increased PCO2 (Di Santo, 2015, 2016; Green and Jutfelt, 2014). Because it is known that Elasmobranchs (sharks, skates, and rays), do not possess the Root Effect, this suggests that they have different mechanism contributing to their maintained aerobic performance. It is possible that Oxygen uptake levels have a genetic basis. Other gaps in the literature included studies relating to freshwater fish. Predictions regarding how PCO2 will affect the aerobic scope of freshwater fish are limited and variable and this is an area that requires further investigation. In addition, data relating to PCO2 effects on oxygen uptake in larval and embryonic stages are also lacking. This is significant because it is well known that these early life stages are some of the most sensitive to environmental perturbations.

Elasmobranchs are cartilaginous fishes (sharks, skates, and rays) (Kok, Albert. Caribbean Reef Shark. Digital image. Wikimedia. N.p., n.d. Web. 23 Mar. 2018).

It is clear that there are many gaps in the literature regarding metabolic responses to increased PCO2. The general trend suggests that, in adult teleosts, at least, aerobic performance is mostly maintained. Although this may sound like good news, it is important to remember that more data and information is still needed and that the effects of increased PCO2 may affect fish populations in the long term and across generations.

Works Cited

Di Santo, V. (2015). Ocean acidification exacerbates the impacts of global warming on embryonic little skate, Leucoraja erinacea (Mitchill). Journal of experimental marine biology and ecology, 463, 72-78.

Di Santo, V. (2016). Intraspecific variation in physiological performance of a benthic elasmobranch challenged by ocean acidification and warming. Journal of Experimental Biology, 219(11), 1725-1733.

Green, L., & Jutfelt, F. (2014). Elevated carbon dioxide alters the plasma composition and behaviour of a shark. Biology letters, 10(9), 20140538.

Hannan, K. D., & Rummer, J. L. (2018). Aquatic acidification: a mechanism underpinning maintained oxygen transport and performance in fish experiencing elevated carbon dioxide conditions. Journal of Experimental Biology, 221(5), jeb154559.

Lüthi, D., Le Floch, M., Bereiter, B., Blunier, T., Barnola, J.-M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H.,Kawamura, K. et al. (2008). High-resolution carbon dioxide concentration record 650,000-800,000 years before present. Nature 453, 379-382. doi:10.1038/nature06949.