Effects of Acidification on Mollusks
Mollusks are "shelled" invertebrates, and their body forms vary widely from clams and scallops, to snails and slugs, to octopus and squid. Not only is this a highly diverse group of animals, it is also the basis of a number of major world fisheries and a large component of global marine aquaculture. In the Mid-Atlantic, bivalve and cephalopod mollusks – clams, oysters, scallops and squid – are among the largest and most valuable commercial fisheries. Bivalve clams and oysters are also the foundation of the majority of marine aquaculture produced in the Mid-Atlantic region.
Shells of mollusks are made of carbonate, a material that can be vulnerable to low pH or acidified conditions. In a recent review of sensitivity of species to changing climate, the shellfisheries of the Mid-Atlantic were identified as particularly high risk for negative impacts due to both acidification and temperature changes. The larval stages of bivalves are especially sensitive to changes in pH and alkalinity, because their shells are thin, newly developing and made of an easily dissolved highly soluble form of calcium carbonate called aragonite. Low pH and undersaturation with regard to calcium carbonate can easily dissolve thin aragonite shells and have been shown in laboratory experiments to lead to reduced survival and growth for bivalve larvae, and have led to production problems in shellfish hatcheries in the Pacific and Northeast.
Evidence also exists which indicates that later life stages of bivalves, whose shells have become thicker and, in some species, shifted to a more stable form of calcium carbonate, may still be susceptible to impacts. These include studies on juvenile clams and oysters. These sensitivities of bivalves to acidification are highly varied among species and life stage, and how they interact with other environmental conditions like temperature and salinity requires further research. Nonetheless, the sensitivity of larval and young juvenile bivalves has important consequences in terms of population stability of these economically and ecologically important species.
Bivalve shellfish are filter-feeders and important coastal ecosystem builders, and are often the focus of restoration and ecosystem resilience planning. To effectively implement coastal resilience or restoration priorities that include shellfish, it is imperative to better understand the ways that future acidified conditions will interact with these species throughout their life cycle.
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