Oyster shell is a crucial component of healthy oyster reefs. Shell planting has been a main component of oyster restoration efforts in many habitats and has been carried out on scales from individual and grassroots efforts to multiagency efforts across entire estuaries. However, the cycling and lifetime of the shell that makes up the bulk of an oyster reef has only recently received attention, and most of the work to date has focused on the role of epi- and endobionts on shell degradation. Here we report findings from a laboratory study in which we manipulated pH in a flow-through control system using water from the mesohaline mouth of the Patuxent River to measure dissolution rates of intact oyster shell. Shells from the Eastern oyster (Crassostrea virginica Gmelin 1791) with three different legacies were exposed to 4 levels of pH that encompass a range typical of the mesohaline waters of the Chesapeake Bay (∼7.2–7.9 on the NBS scale). Mass loss over a 2-wk period was used to measure dissolution rate on 3 shell legacies: fresh, weathered, and dredged. We found that pH and shell legacy had significant effects on shell dissolution rate, with lower pH increasing dissolution rate. Fresh shell had the highest dissolution rate, followed by weathered then dredged shell. Dissolution rates were significantly different among all 4 pH treatments, except between the lowest (∼7.2) and the next lowest (∼7.4); however, shells lost mass even under noncorrosive conditions (∼7.9). We discuss the implications of our findings to ongoing efforts to understand shell budgets and cycling in oyster reef habitat, the interaction of biological and geochemical agents of shell degradation, and the complexity associated with shell carbonate cycling in the unique milieu of the oyster reef.
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Vol. 30 • No. 3