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Coral physiology and microbiome dynamics under combined warming and ocean acidification

Rising seawater temperature and ocean acidification threaten the survival of coral reefs. The relationship between coral physiology and its microbiome may reveal why some corals are more resilient to these global change conditions. Here, we conducted the first experiment to simultaneously investigate changes in the coral microbiome and coral physiology in response to the dual stress of elevated seawater temperature and ocean acidification expected by the end of this century. Two species of corals, Acropora millepora containing the thermally sensitive endosymbiont C21a and Turbinaria reniformis containing the thermally tolerant endosymbiont Symbiodinium trenchi, were exposed to control (26.5°C and pCO2 of 364 μatm) and treatment (29.0°C and pCO2 of 750 μatm) conditions for 24 days, after which we measured the microbial community composition. These microbial findings were interpreted within the context of previously published physiological measurements from the exact same corals in this study (calcification, organic carbon flux, ratio of photosynthesis to respiration, photosystem II maximal efficiency, total lipids, soluble animal protein, soluble animal carbohydrates, soluble algal protein, soluble algal carbohydrate, biomass, endosymbiotic algal density, and chlorophyll a). Overall, dually stressed A. millepora had reduced microbial diversity, experienced large changes in microbial community composition, and experienced dramatic physiological declines in calcification, photosystem II maximal efficiency, and algal carbohydrates. In contrast, the dually stressed coral T. reniformis experienced a stable and more diverse microbiome community with minimal physiological decline, coupled with very high total energy reserves and particulate organic carbon release rates. Thus, the microbiome changed and microbial diversity decreased in the physiologically sensitive coral with the thermally sensitive endosymbiotic algae but not in the physiologically tolerant coral with the thermally tolerant endosymbiont. Our results confirm recent findings that temperature-stress tolerant corals have a more stable microbiome, and demonstrate for the first time that this is also the case under the dual stresses of ocean warming and acidification. We propose that coral with a stable microbiome are also more physiologically resilient and thus more likely to persist in the future, and shape the coral species diversity of future reef ecosystems.

Continue reading ‘Coral physiology and microbiome dynamics under combined warming and ocean acidification’

The last stop: when there’s nowhere colder to go

How climate change is affecting polar fish at the tip of a warming world

Fish have been migrating to cooler water over the last several decades as the ocean warms. But in Antarctica, the coldest place on the planet, polar species have nowhere to go.

Preliminary research by a UC Davis animal scientist shows that some polar fish have been able to acclimate to warm water or to higher levels of carbon dioxide, but not to both.

Continue reading ‘The last stop: when there’s nowhere colder to go’

Coping with climate stress in Antarctica

Coping with climate stress in Antarctica

EA young rockcod swims in Antarctica. Credit: Rob Robbins/US Antarctic Program

Some Antarctic fish living in the planet’s coldest waters are able to cope with the stress of rising carbon dioxide levels the ocean. They can even tolerate slightly warmer waters. But they can’t deal with both stressors at the same time, according to a study from the University of California, Davis.

The study, published recently in the journal Global Change Biology, of emerald rockcod is the first to show that Antarctic fishes may make tradeoffs in their physiology and behavior to cope with ocean acidification and .

(The research is described in a web feature, “The Last Stop,” at the UC Davis Science & Climate website.)

“In dealing with climate stress, these fish are really bad multi-taskers,” said senior author Anne Todgham, an associate professor with the UC Davis Department of Animal Science. “They seem quite capable of coping with increases in CO2, and they can compensate for some warming. But they can’t deal with both stressors at the same time. That’s a problem because those things happen together—you don’t get CO2 dissolving in the ocean independent of warming.”

Tradeoffs

Antarctic fishes live in water that is typically about -1.9C (28.6F). At their field site in Antarctica, the authors exposed emerald rockcod to two temperatures: -1 degree Celsius (30F) and 2 degrees Celsius (36F). The latter is the threshold for that the Paris Agreement targets to prevent the most catastrophic impacts of climate change. They also exposed the fish to treatments of three different levels of CO2 ranging from ambient to elevated projected levels.

Coping with climate stress in Antarctica

Emerald rockcod in Antarctica can handle some increases in temperature and carbon dioxide levels, but not both at the same time. With climate change, you rarely have one climate stressor without the other. Credit: Rob Robbins/US Antarctic Program

Increased CO2 levels by themselves had little impact on the fish. After a couple of weeks, heart, ventilation and metabolic rates increased with warming. Their behavior also changed with warming. The fish swam less and preferred dark zones, which suggests they were attempting to conserve energy. Then after 28 days, juvenile rockcod were able to compensate for the warming temperatures. However, this temperature compensation only happened in the absence of rising CO2.

No colder places to go

While some species are beginning to shift to cooler places to escape habitats, polar have no colder places to go. They have to cope by using their existing physiology, which the study shows is limited.

Emerald rockcod help form the basis of the Antarctic food web, supporting an ecosystem of species such as Emperor penguins and seals.

“The Antarctic has contributed very little to the production of greenhouse gases, and yet it’s one of the places on the planet receiving the most impact,” Todgham said. “I feel we have responsibility to care about the spaces that are so fragile. If we can provide reservoirs of areas that are less stressful to plants and animals through protecting natural places, we can buy ourselves some time to deal with things like that will take a long time to get in line.”

UC Davis (via Phys.org), 16 January 2018. Press release.

Antarctic emerald rockcod have the capacity to compensate for warming when uncoupled from CO2-acidification

Increases in atmospheric CO2 levels and associated ocean changes are expected to have dramatic impacts on marine ecosystems. Although the Southern Ocean is experiencing some of the fastest rates of change, few studies have explored how Antarctic fishes may be affected by co-occurring ocean changes, and even fewer have examined early life stages. To date, no studies have characterized potential trade-offs in physiology and behavior in response to projected multiple climate change stressors (ocean acidification and warming) on Antarctic fishes. We exposed juvenile emerald rockcod Trematomus bernacchii to three PCO2 treatments (~450, ~850, and ~1,200 μatm PCO2) at two temperatures (−1 or 2°C). After 2, 7, 14, and 28 days, metrics of physiological performance including cardiorespiratory function (heart rate [fH] and ventilation rate [fV]), metabolic rate (M˙O2), and cellular enzyme activity were measured. Behavioral responses, including scototaxis, activity, exploration, and escape response were assessed after 7 and 14 days. Elevated PCO2 independently had little impact on either physiology or behavior in juvenile rockcod, whereas warming resulted in significant changes across acclimation time. After 14 days, fH, fV and M˙O2 significantly increased with warming, but not with elevated PCO2. Increased physiological costs were accompanied by behavioral alterations including increased dark zone preference up to 14%, reduced activity by 12%, as well as reduced escape time suggesting potential trade-offs in energetics. After 28 days, juvenile rockcod demonstrated a degree of temperature compensation as fV, M˙O2, and cellular metabolism significantly decreased following the peak at 14 days; however, temperature compensation was only evident in the absence of elevated PCO2. Sustained increases in fV and M˙O2 after 28 days exposure to elevated PCO2 indicate additive (fV) and synergistic (M˙O2) interactions occurred in combination with warming. Stressor-induced energetic trade-offs in physiology and behavior may be an important mechanism leading to vulnerability of Antarctic fishes to future ocean change.

Continue reading ‘Antarctic emerald rockcod have the capacity to compensate for warming when uncoupled from CO2-acidification’

Marine life can buffer ocean acidity, study finds

Tide pools reveal surprising influence of marine life on seawater chemistry. Photo Credit: Ethan Daniels/Shutterstock

Tide pools reveal surprising influence of marine life on seawater chemistry. Photo Credit: Ethan Daniels/Shutterstock

One of the many consequences of rising atmospheric carbon dioxide is ocean acidification—the lowering of seawater pH as CO2 chemically reacts with dissolved ions in seawater. Scientists have found that more acidic waters are dangerous to many species, especially structure-builders like corals, and thus the potential drop in pH predicted in the future would be devastating to marine habitats.So it’s not surprising that many scientists are actively looking for ways to mitigate this for coastal ecosystems, where losses could be especially impactful ecologically and economically. But the answer may be right in front of them: marine life is already able to buffer drops in pH, finds new research in Scientific Reports.

Continue reading ‘Marine life can buffer ocean acidity, study finds’

Biophysical feedbacks mediate carbonate chemistry in coastal ecosystems across spatiotemporal gradients

Ocean acidification (OA) projections are primarily based on open ocean environments, despite the ecological importance of coastal systems in which carbonate dynamics are fundamentally different. Using temperate tide pools as a natural laboratory, we quantified the relative contribution of community composition, ecosystem metabolism, and physical attributes to spatiotemporal variability in carbonate chemistry. We found that biological processes were the primary drivers of local pH conditions. Specifically, non-encrusting producer-dominated systems had the highest and most variable pH environments and the highest production rates, patterns that were consistent across sites spanning 11° of latitude and encompassing multiple gradients of natural variability. Furthermore, we demonstrated a biophysical feedback loop in which net community production increased pH, leading to higher net ecosystem calcification. Extreme spatiotemporal variability in pH is, thus, both impacting and driven by biological processes, indicating that shifts in community composition and ecosystem metabolism are poised to locally buffer or intensify the effects of OA.

Continue reading ‘Biophysical feedbacks mediate carbonate chemistry in coastal ecosystems across spatiotemporal gradients’

Boron isotopes as a proxy for pH in siliceous and calcareous marine algae

Rising CO2 in the atmosphere has directly led to a reduction in surface ocean pH -a process known as ocean acidification. There is a need to understand past climates in terms of ocean pH change in order to be able to relate these to the current effects of climate change on marine organisms. One way of doing this is by measuring boron isotopes in marine carbonates, such as foraminifera and corals, to estimate past ocean pH, and thus to infer past pCO2. Key regions of atmospheric-ocean CO2 exchange are the Southern Ocean and subarctic North Pacific, and they are also areas where modern ocean acidification is occurring fastest. The current application of the boron isotope proxy is restricted in these high latitude regions due to lack of calcareous organisms preserved in the sediment here. Therefore, there is a need to expand the boron isotope proxy into novel materials, such as diatoms and coralline algae, which are found in these key high latitude habitats in abundance.
This thesis aims to investigate whether the hard parts of marine algae (siliceous: di-atoms; calcareous: coralline algae) are suitable archives for the boron isotope pH proxy. This is achieved by examining: (i) which boron species could be incorporated into the frustule/skeleton; (ii) the relationship between boron isotopic composition and seawater pH, and hence the sensitivity of boron isotopes in each organism to changes in seawater pH; (iii) the palaeo-archive potential of each organism. These aims are addressed by developing a method to measure boron isotopes and boron content of diatoms by MC-ICP-MS, calibrating the boron-pH relationships in a species of diatom using culturing experiments, applying this calibration to sedimentary diatoms collected from a core in the subarctic North Pacific, and also by investigating the relationship between boron isotopes and seawater pH in a species of coralline algae.

Continue reading ‘Boron isotopes as a proxy for pH in siliceous and calcareous marine algae’


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