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The Role of Macroalgae in the Ecosystem

January 28, 2019/in SRC blog /by admin

By Haley Kilgour, SRC intern

Seaweeds are well-known to be important primary producers in coastal waters, but they may potentially also play a role in providing refuge from ocean acidification. Macroalgaes such as Laminariales and Fucales, both of which are brown algaes, are ecosystem engineers that influence factors such as water velocity, light penetration, and chemical characteristics of seawater (e.g. via carbonate chemistry, and oxygen and nutrient availability).

Figure 1. A) Ecklonia radiata. B) ephiphyte. While epiphytes come in many shapes and sizes, ranging from looking like hair and snot, to being delicate and flowerlike, they normally grow on top of another plant. Note the epiphyte shown in B is not the epiphyte found on Ecklonia radiata in this study.

The diffusive boundary layer (DBL) exists at the surface of the leaf blade and is the area of the most rapid and variable fluctuations. The DBL is formed when a fluid moves over a solid and no-slip conditions create a region of viscously-dominated laminar flow. Here movement of ions and molecules is by molecular diffusion and the metabolic activity of the organism, in this case, seaweeds, creates a concentration gradient from the uptake and release of dissolved substances to and from the surface of the leaf blade. DBL microenvironments are not only important in the transfer of nutrients and metabolites but are also critical for timing of gamete release and keeping antifouling agents at the blade’s surface. Many organisms such as bacteria, diatoms, various larvae, annelids, and other algae live in this layer.

Over the next century the pH of seawater, on average world-wide, is expected to be reduced by 0 .1-0.3 units. While this change seems to be small, this is in fact quite drastic and will greatly impact corals and their ability to pull calcium carbonate from the water, which is the major component of their exoskeletons. The goal of this study, from Noisette and Hurd (2018), was to: a) study the characteristics of thickness and concentration gradient of DBL at the blade surface of Ecklonia radiata and b) determine the characteristics of DBL in predicted future conditions.

Eighty blades of algae were taken from in situ locations in Hobart, Tasmania, Australia. In the lab, the blades were kept at 13°C and in low light conditions. Different combinations of light, mainstream pH, flow, and epiphytic conditions were evaluated with four blade replicates. Data was then analyzed for significance using three-way ANOVAs with pH, flow, and presence/absence of epiphytes. A three-way MANOVA was then used to compare coefficients of curves fitted to the profiles.

Figure 2. Shows DBL thickness in various treatments of pH, presence of epiphytes, and flow rates.

It was found that pH did not affect DBL while flow and epiphyte presence did. DBL was thicker in slow flow conditions, as well in epiphytic conditions. It was also found that oxygen profiles were steeper in fast flow treatments. Noisette and Hurd also found that epiphytes decreased the oxygen content of the DBL under dark conditions.

It was noted in particular that DBL thickness increased in slow flow because the DBL of the blade and epiphytes actually merged. Metabolic activity of both epiphytes and algae led to variations in oxygen concentration and pH in the DBL which offers potential refuge from future ocean acidification. While blades with epiphytes did have larger DBLs, net photosynthesis was lower due to epiphytes using oxygen produced by the algae and potential shading of the algae that might reduce the efficiency of photosynthesis.

Noisette and Hurd mention that organisms that regularly encounter strong fluctuations, like nearshore algae, might be better able to survive a lower pH of seawater due to higher phenotypic plasticity. DBLs might thus act as refuges for calcifiers and other organisms by allowing them to adapt to lower pH conditions over time. While this offers some room for adaptation of important oceanic organisms, it comes on a small scale. This could be the difference between complete breakdown of ecosystems and hanging on by a thread.

Work Cited

Noisette F & Hurd C. (2018). Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification. Functional Ecology, 32.5: 1329-1342.

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

January 25, 2019/in Conservation, Ocean News /by admin

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.” Wikipedia.org, 22 Aug. 2011, en.wikipedia.org/wiki/File:Keppelbleaching.jpg)

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, earthobservatory.nasa.gov/Features/Paleoclimatology_CloseUp/paleoclimatology_closeup_2.php.
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

January 7, 2019/in Conservation, Ocean News /by admin

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.
(https://commons.wikimedia.org/wiki/File:Fisherman_in_Paje.jpg)

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.

The effects of elevated temperature and ocean acidification on the metabolic pathways of notothenioid fish

November 7, 2017/0 Comments/in Conservation, Ocean News /by aanstett

By Abby Tinari, SRC intern

Notothenioid fish are typically found in the deep, cold waters of the Southern Ocean. Three species of fish native to the Ross Sea were studied to see how they may react to warmer and more acidic oceans.

(a) Pagothenia borchgrevunki (http://adam.antarcticanz.govt.nz), (b) Trematomus newnesi (http://adam.antarcticanz.govt.nz), (c) Trematomus bernacchii (Wikimedia Commons), (d) Ross Sea Location (Wikimedia Commons)

Methods

To measure the effects of temperature on the fish, individuals were randomly selected and placed in one of the four experimental treatment tanks. The experimental tanks consisted of a control treatment, a low temperature and high pCO₂, high temperature and low pCO₂, and high temperature and high pCO₂ to test the individual and overall effects of temperature and pCO₂ on the three-fish species. pCO₂ is the partial pressure of carbon dioxide in the water. Each fish had an acclimation period that lasted anywhere from 7 to 56 days. Measurements of fish condition and growth were recorded over the course of the experiment. A few tests were performed to analyze enzymatic changes in the liver, white muscle tissue, and gills. One of the tests, the citrate synthase activity test measured how well the fish can release stored energy.

Results

T. bernacchii, the emerald codfish, was the only fish to display any significant impact from the treatments. The growth and condition declined significantly due to temperature but slowed as the acclimation period increased. The group of fish with the faster acclimation period had the largest decline of condition and growth, especially those that also had the multi-stress (high temperature and high <em>p</em>CO₂) treatment. The temperature also influenced the Emerald Codfish’s oxygen consumption and metabolic rate. The high <em>p</em>CO₂ tank had a small increase in metabolic rate. There were significant increases in citrate synthase activity, the first of which occurred after 7 days in the multi-stress treatment in the gills. By the 28-day acclimation, all treatments had significantly increased in both the liver and the gills.

The bald notothen, P. borchgrevinki, metabolic rates were significantly affected by temperature in the shorter acclimation periods. Interestingly, the oxygen consumption rates decreased in the high temperature treatments over time. Time and temperature were the main drivers in the citrate synthase activity increase in the gill tissues.

Metabolic rates in T. newnesi differed significantly between the acclimation groups with temperature as the main effect. No significant difference between pCO₂ and temperature was present. There was however, an increased oxygen consumption rate after the 7 and 28-day acclimation period. The T. newnesi showed the least sensitivity to the treatments. The changes in Citrate synthase activity were not statistically significant.

Citrate synthase enzyme activity (±SE) of Trematomus bernacchii gill (A) and liver tissues (B), Pagothenia borchgrevinki gill (C) and liver tissues (D) and Trematomus newnesi gill (E) and liver tissues (F) acclimated at 7, 28 and 42 or 56 days to a control treatment (low temperature + low pCO2; black bars), low temperature + high pCO2 (white bars), high temperature + low pCO2 (dark gray bars) and high temperature + high pCO2 (light gray bars with cross hatches). Groups not connected by the same letter are significantly different from each other. (Enzor et al. 2017)

Discussion

This group of fish, the Notothenioid fish are critical to the Ross Sea food web. The three-species studied are consumed by seals, penguins, and other top predators. Studies like this one help to predict population responses for not only the Notothenioidei suborder but also other species which depend on these individuals for food.

Temperature had a greater adverse effect on the energy demands for two of the studied species. The fish may be able to acclimate to the higher temperatures, but only to an extent. Higher temperatures may mean a decreased ability to efficiently ingest food leading to decreased growth and other detrimental effects as seen in the Emerald codfish.

It should be noted that the long-term implications of the temperature and pCO₂ on growth should be cautiously interpreted due to the small sample size and lack of growth even in the control samples.

References

Enzor LA, Hunter EM, Place SP (2017) The effects of elevated temperature and ocean acidification on the metabolic pathways of notothenioid fish. Conserv Physiol 5(1): cox019; oi:10.1093/conphys/cox019

Ocean Acidification and Its Effect on Bacterial Communities

March 22, 2016/0 Comments/in Conservation, Ocean News /by aanstett

By Casey Dresbach, SRC Intern

The pH of the ocean is changing incrementally, as a result of increases in atmospheric carbon dioxide. As shown in Figure 1, a proceeding decline in seawater pH has been induced by ocean acidification and will continue over the next hundred years. The ocean is expected to decline an average of 0.3 pH units by the end of the century. Changing the geochemistry of the ocean is consequently changing the biogeochemical processes of the sea, including marine microbial populations. The microbial community is extremely important to the marine carbon cycle in their role to decompose and recycle nutrients, as shown in Figure 2.

Figure 1. Predicted Ocean Surface pH Through the Year 2100.

The ocean maintains a viable level of carbon dioxide from such decomposition and subsequent respiration of organic molecules by heterotrophic bacteria. Since the industrial boom, the human obsession to industrialize is continually offsetting the balance of the ocean’s carbon dioxide levels and setting up a future of mutational distress. The burning of fossil fuels (primarily coal) and its emissions are manipulating the ocean for the worse.

Figure 2. Microbial communities graze, break down, recycle and respire nutrients in the ocean helping to maintain an interconnected web of carbon transfer.

Researchers Ian Joint, Scott C. Doney, and David M Karl wrote an article for the ISME Journal regarding their perspectives on the question, “Will ocean acidification affect marine microbes?”

The reasoning behind their perspective has much to do with the lack of proper research done addressing the issue of microbial function in a lowered pH oceanic environment. Much is known about calcifying organisms, such as corals and coccolithiphores, in regards to ocean acidification. With an increase in acidity, maintaining calcite and aragonite shells and skeletons becomes nearly impossible.

Most studies that are published include discussions of the ocean pH in the context of geological time scales in spatial uniformity of pH for the present-day ocean. However, pH of the oceans is not constant and there are considerable seasonal, depth, and regional variations that come into play. With that in mind, pH is naturally variable and marine organisms-particularly microbes-must already be capable of adapting to rapid and sometimes large changes in pH. Kai T. Lohbeck, Ulf Riebesell and Thortsten B. H. Reusch published an article for Nature Geoscience regarding the topic of adaptive evolution of a key phytoplankton species to ocean acidification. According to the article, they suggested that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change; that these organisms are currently facing evolutionary adaptations.

The pH levels in the ocean are not consistent, especially when considering other variables such as light, temperature, and depth. The multifactorial relationship among these variables is direct. Researchers Ian Joint, Scott C. Doney, and David M Karl presented a null hypothesis to be tested: marine microbes posses the flexibility to accommodate pH change and there will be no catastrophic changes in marine biochemical processes that are driven by phytoplankton, bacteria, and archae.

In an alternate scientific publication by J. Piontek, M. Lunau, N. Händel, C. Borchard, M. Wurst, and A. Engel, a study was conducted in regards to acidification increasing microbial polysaccharide degradation in the ocean. The ocean’s capacity for carbon dioxide storage is strongly affected by biological processes whose feedback potential is unfortunately difficult to evaluate. This article coincides with the previous considering that very little is known about potential effects ocean acidification poses not only on the microbial community themselves, but on bacterial degradation activity as a whole. Polysaccharides are a major component of organic matter, an energy source for the majority of bacterial communities. Their breakdown by bacterial enzymes seemed to have significantly accelerated during J. Piontek, M. Lunau, N. Händel, C. Borchard, M. Wurst, and A. Engel’s experimental simulation of ocean acidification. An experiment was set up to test the rate of enzymatic polysaccharide hydrolysis (how quickly bacteria could break down the macromolecule) in natural bacterioplankton communities. In this experiment, two environments were simulated: one being present day pH levels – what the ocean’s pH level is today and the latter being future day pH levels – what the ocean’s pH levels are predicted to be in the next hundred years. After each sample was incubated, concentrations of dissolved and particulate combined glucose, galactose, arabinose, and other sugars and acids were also detected. These concentrations represented the complexity of the relationships between the variables that come into play with acidification. This allowed the scientists to relate the differences in glucosidase activity (enzymes which break down glucose) and macromolecule concentration between present-day and future-ocean treatment to the increase in hydrogen ion concentration. Figure 3 illustrates the results of the above experiment with regards to an additional variable, permanent dark incubation and dark cycling incubation. The experiment revealed that the observed increase in glucosidase activity was directly proportional to the increasing acidity of the ocean water in a simulated acidification model. They also came to realize that changes in the enzymes’ activities reflected a community response of bacterioplankton to the simulated acidification as well. A collective conclusion of the experiment goes as follows: experimental results suggest that increased glucosidase activity at lowered seawater pH does not depend on the abundance of some specific bacterial strains, but reflects a community response to lowered seawater pH. This response could indicate that bacterial communities are currently undergoing adaptations to adjust to the decreasing pH. Higher enzymatic rates at lowered seawater pH are a chemical acidification effect on natural enzyme assemblages that is beneficial for the bacterial metabolism. Some might go on to further assume that come a more acidic oceanic environment, bacterioplankton communities will readily adapt and will not counter enhanced polysaccharide degradation. With a quicker degradation of polysaccharides, the bacterioplanktonic communities might flourish, quicker breakdown of sugars to be used as an energy source while simultaneously recycling nutrients back into the food web during degradation.

Figure 3. Percent loss of different macromolecules in present day oceanic pH levels and future pH levels with regards to another variable: permanent dark incubation and dark cycling incubation.

Results from different studies and perspectives show that a lot of variables must be considered when focusing on the question, “Will ocean acidification affect marine microbes?” Current analysis and comparison of freshwater pH and seawater pH is only so significant because the pH in freshwater acts on a short-term scale and the ocean acts on a far longer term. The ocean is too complex; there are too many variables to continue with the current broad-scale state of research.. Studies should go into the “micro-economics” of the ocean and its harmful relationship with acidification. There is more potential for a better understanding of a correlation between microbial communities and ocean acidification if things are broken apart and analyzed. Studying and analyzing the consequences of changes in individual variables, such as a potential threat to a major energy source of microbial communities (polysaccharides), can infer if there is in fact a present evolutionary adaptation of microbes to the increasingly acidic ocean. It’s also important to consider the possibility that microbial communities will adapt to the changes in pH but only to a certain degree before the rate of adaptation plateaus and these communities can no longer keep up with the consistent decrease in pH in the next one hundred years.

Resources

Ian Joint, S. C. (2010, June 10). Will ocean acidification affect marine microbes?. ISME Journal.

Piontek, M. L. (2010, May 19). Acidification increases microbial polysaccharide degradation in the ocean. Biogeosciences.

Kai T. Lohbeck, U. R. (2012, April 8). Adaptive evolution of a key phytoplankton species to ocean acidification. Nature Geoscience.

Oakes, M. (2013, June). Changes: Forecase for Marine Mircrobial Communities. Retrieved February 21, 2016, from Antarctica: http://www.antarctica.gov.au/magazine/2011-2015/issue-24-june-2013/science/changes-forecast-for-marine-microbial-communities

Stocker, T. D. K. Climate Change 2013: The Physical Science Basis. Cambridge and NY,UK and USA: IPCC.

Ocean acidification alters fish populations indirectly through habitat modification

January 14, 2016/1 Comment/in Conservation, Ocean News /by aanstett

By Shannon Moorhead, SRC Intern

In recent years, it has become apparent that increased CO₂ emissions have farther reaching consequences than simply raising the temperature of Earth’s atmosphere. A significant amount of CO₂ is absorbed by the ocean, which raises its acidity through chemical reactions with water molecules. This process, termed ocean acidification, has a large number of potentially detrimental effects on biodiversity, interactions between species, and individual species fitness. Elevated CO₂ levels encumber the ability of certain invertebrates, such as corals and snails, to build calcium carbonate skeletons and can drive habitat shifts that degrade ecosystems. Laboratory experiments have also shown that prolonged exposure to CO₂ negatively affects the ability of fish to perform predator-avoidance behaviors.

Nagelkerken et al 2015 explores the effects of ocean acidification with in situ study, meaning the experiment was done in the natural habitat of the subject species. A field study allowed for the researchers to account for the indirect effects of changes in habitat on fish behavior and abundance, necessary to more accurately predict species responses to ocean acidification, as well as their potential consequences for ecosystems. The authors observed habitat coverage, fish habitat association, fish escape response performance, and fish and predator population density at 2 separate locations: White Island, New Zealand and Vulcano Island, Italy. Both sites are characterized by vents that naturally produce CO₂, maintaining the acidity of the surrounding water at a much higher than average level, levels that the rest of the oceans may reach by the end of the century.

a,b, Habitat cover at White Island (a) and Vulcano Island (b). c,d, Fish density in each habitat at White Island (c) and Vulcano Island (d)

At both locations, habitat coverage changed significantly between the control sites (far enough away from the vents to not be affected by the elevated CO₂) and the sites near the vents. Increased acidity caused ecosystem phase shifts; complex ecosystems mottled with vegetation, algae, patches of rock or sand give way to simpler communities dominated by either algae or sand near the vents. The fish species observed, the common triplefin and Bucchich’s goby, both associated primarily with algae and sand or rock bottom areas. Increased biomass of preferred habitat, along with higher levels of prey abundance in these habitats, most likely contribute to the significant difference in fish density observed between the vent and control sites. Fish density near the vents was greater than double density measured at control sites. This may have also been a result in part of the lack of predatory fish observed near the CO₂ vents.

a, fish escape speed at White Island (top panel) and Vulcano Island (bottom panel). b, jump distance (distance fish moved while escaping) at White Island (top panel) and Vulcano Island (bottom panel). c, startle distance at White Island (top panel) and Vulcano Island (bottom panel)

Though effects of elevated CO₂ actually improved fish abundance, it still had negative effects on the behavior of the fish species. Fish at vent sites escaped threats more slowly than fish at control sites and usually waited until the threat was closer to begin moving away, indicating CO₂ exposure lessened the ability of the fish to avoid predation. One exception to this, in the algae dominated habitats at the Vulcano Island site, there was little difference between the startle distance (distance from the threat to the fish when the fish starts its escape) of fish living at the control sites and fish living near the vents. Fish may begin their escape response later in this habitat because they feel more relaxed knowing they have easy access to shelter.

a, fish density at White Island and Vulcano Island. b, predator density at White Island and Vulcano Island

This study is the first example of the negative direct effects of ocean acidification on fish behavior being counteracted by indirect effects that actually increase fish abundance and survival. Contrasting laboratory-based predictions that less productive and simpler ecosystems would harm fish populations, this paper demonstrates the need for more in situ studies on the effects of elevated CO₂ levels. Indirect effects, such as changes in predator and prey abundance and habitat phase-shifts, must be considered when attempting to accurately predict the consequences of climate change.

Nagelkerken I, Russel BD, Gillanders BM, Connell SD (2016) Ocean acidification alters fish populations through habitat modification. Nature Climate Change 6: 89-93

Rising Ocean CO2 Levels are Hurting Cephalopods

March 11, 2015/0 Comments/in Conservation, Ocean News /by aanstett

by Jessica Wingar, RJD intern

In the last decade, the concerns of how global climate change is going to affect our planet have grown. One of the main components of what is causing this climate change is the increase in carbon dioxide in our environment. There was a major increase in carbon dioxide in the atmosphere after the industrial revolution. The level of carbon dioxide in the atmosphere has risen from 280ppm to 390ppm. The carbon dioxide from the atmosphere diffuses into the ocean, which has created an increase in carbon dioxide in the ocean. With the increasing carbon dioxide levels in the ocean, the pH of the ocean will decrease leading to many detrimental effects on the animals that live there. It is predicted that by 2300 the carbon dioxide levels in the ocean will be around 1900 μAtm, which will cause the pH of the ocean to drop by 0.77. This decrease in pH will cause extreme changes in the ocean and how organisms develop and survive under these conditions is of utmost importance (Heuer, R., 2014). One of the many classes that has been studied is cephalopoda. The cephalopods include such animals as squid, cuttlefish, and octopus. They are a very important class to ocean trophic levels and to the economy and it is essential to determine what negative effects will occur to them in the coming years (Kaplan, M.B., 2013).

One of these economically important species is Doryteuthis pealeii, the longfin squid. Squid are a critical part of the food chain in the ocean because not only do they serve as prey for many organisms, such as tuna, but they also serve as predators of many organisms. In a study conducted in 2013, this certain species of squid was used. D. pealeii lives in shallow waters in coastal regions. In this study, individuals were taken from Vineyard Sound, Massachusetts on two separate occasions during their breeding seasons which lasts from May to August. The aim of this study was to calculate the difference in mantle size, statolith size, statolith characteristics, and hatching time between control embryos and embryos at an elevated carbon dioxide level of about 2200 μAtm. This is slightly above the predicted levels for the year 2300. The study found that in both trials, embryos hatched later in the carbon dioxide treatment than the control embryos. For example, in the first trial on the first day of hatching, 62.6% of embryos hatched, whereas only 0.7% of the embryos with increased carbon dioxide hatched. The negative effects of this delay may be that there is an increased chance for predation.

Picture 1: Embryo hatching times for both trials

In addition to the hatching time, there were also many other negative changes in other parts of the squid. When the mantle length was looked at between the two conditions, the mantle was significantly shorter when the squid was reared in the carbon dioxide conditions. With a shorter mantle, the squid has less ability to move. Therefore, a shorter mantle can lead to slower swim speeds and lower migration causing a smaller chance of survival. Squid also have statoliths, which are calcified structures that are critical in balance and how the animal moves in the water. Seeing as these are calcified structures, their formation is greatly related to the acid content in the water. In this study, it was found that the statoliths of the squid in carbon dioxide had decreased surface area and a greater likelihood of abnormal shape and abnormal porosity. With decreased function of the statolith, the squid cannot orient itself the correct way in the water and again has decreased survival (Kaplan, M.B., 2013). Along with this type of cephalopod, cuttlefish also show a change in an inner calcareous structure in increased carbon dioxide conditions.

Picture 2: Average statolith surface area in the control treatment vs. the carbon dioxide treatment

Some cuttlefish have a calcareous structure called a cuttlebone that is located dorsally that goes from just behind the head to the end of its body. The purpose of this bone deals with buoyancy. During the day, the chambers of the cuttlebone are filled with fluid, which make the cuttlefish able to sink, and at night this fluid is expelled, which causes the cuttlefish to stay in the same place in the water column. A study done on Sepia officinalis, the common cuttlefish, looked at morphological changes in the cuttlebone in a carbon dioxide rich environment. In this study they found that carbon dioxide exposed cuttlebones had significantly less height and length, but had a 20-55% increase in mass. The shorter height can be accounted for by the fact that the lamellae in the cuttlebone in the carbon dioxide treatment were a lot closer together, compacting the cuttlebone. In addition, the inner pillars of the cuttlebone were found to have doubled in thickness, showing a build up of carbonate and an increase in mass. A heavier cuttlebone is detrimental to a cuttlefish because in order for that structure to control buoyancy it needs to be as light as possible; the cuttlefish will not be easily able to move up the water column because it will take more work to make the animal neutrally or positively buoyant. In addition, it will be more difficult for the cuttlefish to maintain a position in the water column while hunting, which could cause starvation in the organism (Gutowska, M.A., 2010).

Average cuttlebone measurements in the control vs. carbon dioxide treatments

Research into the consequences of ocean acidification is increasingly necessary in order to determine what will happen to the ocean in the next few hundred years. The spike in the carbon dioxide content in the oceans has been directly caused my humans and it is imperative that now something is done to slow down this increase.

References
Gutowska, M.A., Melzner, F, Pörtner, H.O., and Sebastian Meier. (2010). Cuttlebone calcification increases during exposure to elevated seawater pCO2 in the cephalopod Sepia officinalis. Marine Biology, 157 (7): 1653-1663.

Heuer, R.M., and Martin Grosell. (2014). Physiological impacts of elevated carbon dioxide and ocean acidification on fish. American Journal of Physiology, 307 (9): R1061-R1084.

Kaplan, M.B., Mooney, T.A., McCorkle, D.C., and Anne L. Cohen. (2013). Adverse Effects of Ocean Acidification on Early Development of Squid (Doryteuthis pealeii). PLOS ONE, 8 (5): 1-10.

“Near-future Ocean Acidification Will Require Single-Species Approach to Management”

January 23, 2015/0 Comments/in Conservation, Ocean News /by aanstett

By Stephen Cain, RJD Intern

It’s difficult to predict the effects of near-future ocean acidification (OA) across ecoregions and ocean habitat. The body of research has been conducted under a variability of circumstances and conditions. While evidence continues to mount for OA as a global mega trend, researchers like Christopher E. Cornwall and Tyler D. Eddy call for the need to contextualize OA within local coastal communities. It is there, after all, that the combined effects of pollution, resource extraction, and preservation interact within geographically distinct units. The results of multiple stressors, anthropogenic or otherwise, can alter an ecosystem’s structure and function. In their recent study, Cornwall and Eddy suggest that management regimes rely on current global predictions as well as modeling of single-species’ response to changes in ocean chemistry.

For their study, Cornwall et al. used the intertidal and subtidal habitats from the Wellington south coast, and the Taputeranga Marine Reserve off New Zealand. Both possess similar substrate and habitat, and fall within the larger Cook Strait Region. Wellington features extant commercial and recreational fisheries that primarily target Lobster (Jasus edwardsii), Abalone (Haliotis australis and Haliotis iris), as well as Blue Cod (Parapercis colias) and Butterfish (Odax pullus). According to cited work by Breen & Kim (2006), Cornwall et al. note at the time of study that Lobster abundance had been maintained at 20% of original unfished biomass. Taputeranga Marine Reserve (MR), by contrast, was established as a no-take zone at its outset in 2008.

Jasus edwardsii (http://commons.wikimedia.org/wiki/File:Jasus_edwardsii_02.JPG)

Building on a model developed by Eddy et al. (2014), Cornwall and Eddy describe the challenge of scaling down global predictions of OA to their study area. In the body of literature, the effects for net-calcification have been generated from a variety of “carbonate chemistry conditions.” The resulting baselines do not, on their own, serve as complete proxies that the research team could use to base their predictions on. They relied on calculating levels of “dissolved inorganic carbon and total alkalinity, pH on total scale, and partial pressure of CO2” in the survey area, and compared this to the predicted rise of CO2 concentrations between 2014 (380 ppm) and 2050 (550 ppm).

To measure the ecosystem dynamics they used Eco-modeling software EwE. They examined a fully factored set of scenarios comprised of four criteria: fished areas (Wellington), non-fished areas (MR), and the presence or absence of OA. In order to generate estimates for 2050, fishing mortality was held constant from 2008 biomass. The scenario for fished area with an absence of OA was used as the baseline of the study. To further delineate changes over time, four indicators of ecosystem interaction were synthesized:

Proportion of benthic biomass affected
Proportion of pelagic biomass affected
Impact by Trophic Level
Mean Trophic Level of community

After initial modeling, they noted that certain species showed dramatic changes in abundance across scenarios. Further sensitivity analyses, referred to as “blanket modifiers,” strengthened their assumptions about the changes in food web interaction and ecosystem function. One of the more noteworthy findings were the predictions of abundance for Lobster, a keystone species. Outside of the marine reserve Lobster numbers were maintained, albeit at a “fraction” of their original unfished biomass. In a scenario of MR + OA in 2050, however, Lobster abundance was reduced by 42%. This was due to heightened sensitivity to OA. As a result, researchers predicted there would be fewer predations on species at lower trophic levels, and subsequent shifts in the structure of the food web. In that same scenario, “Abalone, piscivorous fishes, and herbivorous fishes increased in biomass by 52%, 11%, and 13% respectively.”

These results may be counterintuitive because there is the expectation that protected areas better compensate for additional stressors than do areas under fishing exploitation. This is the case, and that was what the team correctly hypothesized. However, Cornwall et al. point out the nuances of near-future ocean acidification at a species-specific level. They maintain that the effects will be “subtle, species specific, and context dependent.” Apart from calcareous species, not all species stand to lose, and, in fact, some may flourish. Cornwall and Eddy suggest that these findings can be useful when comparing regions, and targeted catches of species, especially those that will face increased pressure from changes in ocean chemistry.

Ocean Acidification and Your Dinner: Impacts of Marine Seafood

January 21, 2013/0 Comments/in Conservation /by aanstett

By Emily Rose Nelson
RJD Intern

Ocean acidification is a term commonly used in the world of marine science. This process can most easily be described as the lowering of oceanic pH due to increased atmospheric carbon dioxide concentrations. However, there is much more to this complicated process, which could mean great changes for the future of our oceans.

It is no surprise that atmospheric carbon dioxide levels are increasing. Since the industrial revolution atmospheric CO2 concentrations have increased from 280 ppm to 396 ppm, and this number is expected to increase to 800 ppm by the year 2100. Unfortunately, much of this excess CO2 finds its way to the ocean, changing the natural chemistry of the water. When atmospheric CO2 is added to seawater a series of chemical reactions naturally occurs. The addition of excess CO2 shifts the equilibrium of this reaction series, resulting in increased hydrogen and lower carbonate concentrations. Because pH is equal to –log [H+] increased H+ concentrations have lowered the pH from pre-industrial 8.2 to a 7.8 (projected 2100). Carbonate is essential for calcifying organisms such as mussels, shrimp, some coral species, and more. Carbonate ions combine with calcium ions naturally found in seawater to form CaCO3, the skeletal material for many organisms. Lowered carbonate concentrations make it more difficult to form this compound, thus more difficult to calcify, and in some cases survive.