WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2019 27 shells and skeletons. This may reduce the growth of calcifying organisms if they cannot get the resources needed to build their shells. In addition, the increased H+ ion concentration can lead to dissolution of calcium carbonate shells. The consequences of these reactions can have massive impacts within marine ecosystems and detrimental effects on economies globally. In 2014, total domestic commercial bivalve landings in the United States exceeded 73,000 t with a total value of $895 million (National Marine Fisheries Service 2015). A decline in the production of bivalves would hurt the economy of many coastal communities in the US. Current research is seeking to understand the exact impacts of ocean acidification on bivalves so that we can understand the underlying mechanisms and begin to prepare mitigation strategies for potential losses, such as identification of resilient stocks and species or developing approaches and methods to reduce the impact of acidification on vulnerable species. Oysters and Ocean Acidification Many studies suggest that the early life stages of bivalves are highly vulnerable to the effects of ocean acidification. This includes the eastern oyster Crassostrea virginica. Prior to settling and becoming recognizable juvenile oysters, eastern oysters spend the first few weeks of life as vulnerable, free-swimming larvae. As larvae, they pass through several developmental stages and begin to grow a calcium carbonate shell. If the supply of calcium carbonate during development is limited, larvae may not develop properly or die. Numerous studies have classified the effects of ocean acidification on development and shell growth, but less studied are the effects of acidification on oyster physiology and the potential mechanisms that may enable vulnerable larvae to survive and adapt. Research described in this article was designed to understand the impacts of ocean acidification on the eastern oyster. Specifically, Ocean acidification has become a hot topic in the last decade, as we are rapidly recognizing its implications for life in the ocean. Ocean acidification, also referred to as “the other CO2 problem” (Doney et al. 2009), is one of the forms of climate change we are facing as CO2 emissions continue to rise. As CO2 enters the air, primarily by burning fossil fuels (USEPA 2019), most of that CO2 is taken up by the ocean. Although this may benefit the atmospheric climate by reducing the CO2 that would otherwise lead to increased atmospheric warming, it can lead to major changes in ocean chemistry. The hydrolysis of CO2 in water leads to the production of H+ ions that results in a decrease of ocean pH. Since the Industrial Revolution, atmospheric CO2 has increased from 280 ppm to a record peak of 415 ppm in May 2019 (Munroe 2019). This increase in CO2 has resulted in a decrease in ocean pH from 8.2 to 8.1. Although this may seem like a small change, by the end of the century, in the next ~80 years, and under worst-case-scenario conditions, atmospheric CO2 may rise as high as 1000 ppm and pH is expected to drop to 7.8 globally, according to the Intergovernmental Panel on Climate Change (IPCC 2014). The scale of this increase is occurring at a rate one order of magnitude faster than it has ever occurred in the past one million years (Doney et al. 2009). In addition, the pH along coastal areas is even lower on average than the global ocean pH, caused by heightened microbial respiration from eutrophication. In areas such as embayments around Long Island, NY, pH has already reached 7.6 in the summer, markedly lower than that predicted for the global ocean by 2100. For this reason, researchers and stakeholders are concerned about the ability for ocean life to acclimate and adapt long term to the changes in the ocean. Most notably, species that build calcium carbonate shells may be the most vulnerable to changes in ocean chemistry. Along with increasing H+ ion concentration in seawater, when CO2 reacts with water, the carbonate ion concentration in seawater decreases (less saturated), resulting in less carbonate for calcifiers to build their Effect of Food Resource Availability on Resilience of Eastern Oyster Larvae to Ocean Acidification Michelle Barbosa, Caroline Schwaner, Teresa Schwemmer, Emmanuelle Pales Espinosa and Bassem Allam (CONTINUED ON PAGE 28) Numerous studies have classified the effects of ocean acidification on development and shell growth, but less studied are the effects of acidification on oyster physiology and the potential mechanisms that may enable vulnerable larvae to survive and adapt. Research described in this article was designed to understand the impacts of ocean acidification on the eastern oyster. Specifically, the study assessed the effects of acidification on survival, growth and metabolic rates of oyster larvae. In addition, the study began to identify the processes that may enable survival by first assessing whether food availability enhances resilience of these early life stages. These questions are particularly important because a decrease in survival and size of larvae can significantly impact the commercial industry as a result of decreased yield. Studying metabolic rates is vital to understanding the health of an organism as it can indicate whether an animal is under stress or has high energetic demands that must be met with high food availability.
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