Blooms at Lower pH Levels Could Upset Ocean’s Acidification Cycle

by Max Breitbarth

Ocean acidification—the absorption of atmospheric CO2 by the ocean—has increased due to anthropogenic emissions of CO2, resulting in growing concentrations of CO2 in our oceans. Flynn et al. (2015) created models based on projections of increasing ocean acidity to explore the effects of algae blooms at decreasing pH levels and the effects of these blooms on phytoplankton populations that keep the ocean’s acidity within a manageable spectrum. Continue reading

Two Types of Science, One Study of Ocean Acidification

by Weronika Konwent

Ocean acidification is predicted to increase as global warming accelerates, affecting marine habitats and especially coastal areas experiencing episodic upwelling, such as the California Current Large Marine Ecosystem (CCLME). Hofmann et al. (2014) are studying this particular habitat due to its wide variety of conditions and its particular susceptibility to rapid environmental change, To do this, they are using data collected by the Ocean Margin Ecosystems Group for Acidification Studies (OMEGAS) to pair oceanographic and biological data to create a more thorough understanding of genetic variability within key species populations, and how this can affect adaptation to the conditions caused by climate change. Using the biological data to measure responses of sea creatures to oceanographic factors that are affected by climate change, Hofman et al (2014) hope to plot the future survival of CCLME species. Continue reading

Ocean Acidification Improves Marine Snail Prey Response to Predator but Not Shell Growth

by Jennifer Fields

Ocean acidification is known to have an impact on the calcified structure of many marine invertebrates. However, there is recent evidence to suggest that ocean acidification also impacts other key biological processes, such as survival, growth, and behavior. Manríquez et al. (2013) observed the impacts of ocean acidification on shell growth, survival, metabolism, and self-righting ability of a marine gastropod. The authors found there was no significant impact of ocean acidification on net shell growth, survival, or metabolism; however, increased CO2 resulted in faster self-righting times in the marine gastropod. Faster self-righting behavior can reduce the duration of vulnerability to predators and chance of being dislodged by waves of intertidal gastropods. The behavior could be a positive consequence of ocean acidification on marine invertebrates that use a turnover response as a common trait for avoid predation and wave removal. This adaptive trait could induce a co-evolution between predator and prey that would alter predator-prey dynamics within the whole intertidal ecosystem. Continue reading

Marine Mollusc Anti-predator Escape Behavior Impaired with Future Ocean Acidification

by Jennifer Fields

Ocean acidification is known to have significant impacts on marine invertebrates in terms of calcification and reproduction; however, the effects of increased CO2 on marine invertebrate behavior are largely unknown. Watson et al. (2014) predicted marine conch snail predator-escape behavior to its predator cone shell would be impaired with near-future CO2 levels. The authors found that the decision-making of the conch snail was in fact impaired by ocean acidification, leaving the snails more vulnerable to predation. The change in behavior was fully restored by treatment with gabazine, suggesting that changes in acid-base regulation caused by increased CO2 in the ocean interfere with the invertebrate’s neurotransmitter receptor function. These alterations in behavior in marine invertebrates could have wide-ranging implications for the whole entire marine ecosystem. Continue reading

Comparing the Near-Future Effect of Temperature and Acidification on Early Life History Stages of Corals

by Dawn Barlow

Both ocean temperatures and pH are projected to increase due to climate change in the near future—it is predicted that temperatures will be raised by 2°C and that acidity will increase by ~0.2 pH units by the end of the century. While much investigation has been done on the effects of temperature and acidity on the ability of adult corals to form the structure necessary to maintain the integrity of the reef, Chua et al. (2013) investigated the direct effects of increased temperature and acidity on the early life history stages of corals. They looked at fertilization, development, survivorship, and metamorphosis of coral larvae under control conditions as well as under elevated temperature and acidity, both separately and in combination. When the two factors were combined, the results were inconsistent. Overall, the conclusion drawn from this study was that acidification alone is unlikely to be a direct threat to early life history stages of corals, at least in the near future. Increasing temperature, on the other hand, was found to increase the rate of larval development and thereby affect coral population dynamics by changing patterns of connectivity. Continue reading

Seawater Acidity Reduces the Physiological Ability of Corals to Calcify

by Dawn Barlow

This study by Venn et al. (2013) addresses how ocean acidification reduces the calcification rate of corals by reducing internal pH at the calcifying tissue-skeleton interface. They aim to predict how corals will respond and potentially acclimate to ocean acidification by looking at how acidification impacts the physiological mechanisms that drive calcification itself. Coral skeletons are formed from calcium carbonate crystals (aragonite), produced in the fluid-filled subcalcioblastic medium (SCM), which underlies the calcifying tissue. The calcifying tissue elevates pH the SCM relative to the pH of the exterior seawater, favoring the conversion of bicarbonate to carbonate, and enhancing precipitation at the site of calcification. This ability of corals to regulate internal pH is anticipated to be critical in their resilience to ocean acidification, and overall, findings from this study suggest that reef corals may be able to mitigate the effects of seawater acidification by regulating pH in the SCM. Continue reading

The Other Ocean Acidification Problem: CO2 as a Resource

by Dawn Barlow

This study addresses the effects of enhanced CO2 levels in the ocean by looking at how increased acidity might indirectly cause phase shifts in community structure of coral reef and kelp forest ecosystems in temperate and tropical waters. Under elevated acidity and temperature conditions, productivity of certain photosynthetic organisms such as mat-forming algae (low-profile ground-covering macroalgal and turf communities) can increase, making CO2 not only a direct stressor but also an indirect stressor by being a resource for certain competitive organisms, creating enormous potential for shifts in species dominance. Additionally, ocean acidification acts together with other environmental stressors and primary consumers, and these factors also influence community response to acidic conditions. Connell et al. (2013) investigate the prevalence of mat-forming algae in three different scenarios where CO2 levels were either ambient or elevated: in the laboratory, in mesocosms in the field, and at naturally occurring CO2 vents that locally alter the seawater chemistry. They find that in all the scenarios, the algae mats respond positively to the elevated conditions, increasing growth rate and cover to so that the algae became a majority space holder regardless of any herbivory. This is likely because the new environmental conditions favor species with fast growth and colonization rates and short generation times, and these are the species that are capable of completely… Continue reading

Impaired Learned and Lower Prey Survival Under Elevated CO2 Caused from Neurotransmitter Interference

Ocean acidification is known to have physiology impacts and large ecological consequences on marine species. However, the mechanisms by which these impacts occur are somewhat unknown. Chivers et al. (2013) studied the effect of end of century CO2 concentrations on the ability of larval damselfish to learn to identify predators. The damselfish were exposed to a predator odor coupled with an alarm cue designed to stimulate learning within the fish to learn to avoid that predator. The fish were then exposed the odor a few days later to see if they had successfully learned to identify the predator. Fish were then put in the wild and the survival rate was monitored. The authors found that there was impaired neurotransmitter function within the elevated-CO2 fish. This impaired learning was reversed with gabazine, an antagonist of the GABA-A receptor—a neurotransmitter that manages risk assessment in vertebrates. Overall, elevated CO2 lead to an impairment in learning within the lab setting and also lowered fish survival rates in the wild. With lower survival as a result of impaired learning, there could be negative implications for reef population recruitment as well as changes in species dynamics with near future CO2 concentrations.–Submitted by Jennifer Fields

Chivers, D.P., McCormick, M.I., Nilsson, G.E., Munday, P.L., Watson, S.A., Meekan, M.G., Mitchell, M.D., Corkill, K.C., Ferrari, M.C.O. 2013. Impaired Learning of Predators and Lower Prey Survival Under Elevated CO2: a Consequence of Neurotransmitter Interference. Global Climate Change published ahead of print May 30, 2013,doi:10.1111/gcb.12291

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