Science Inventory

In situ recovery of bivalve shell characteristics after temporary exposure to elevated pCO2

Citation:

Grear, J., A. Pimenta, H. Booth, D. Horowitz, W. Mendoza, AND Matthew Liebman. In situ recovery of bivalve shell characteristics after temporary exposure to elevated pCO2. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 65(10):2337-2351, (2020). https://doi.org/10.1002/lno.11456

Impact/Purpose:

There is now significant concern about the addition of carbon dioxide to coastal waters that occurs during the metabolism of organic material loaded externally from watersheds or produced in excess as a response to nutrient enrichment. In coastal areas, this carbon dioxide combines with carbon dioxide that enters the oceans from the atmosphere, thereby resulting in a nutrient-driven enhancement of what was formerly thought to be a purely ocean-driven acidification process. Among the first stakeholders already being affected by this enhanced acidification are shellfish hatcheries, growers, and harvesters. However, most research on shellfish has focused on laboratory responses in the larval life stage. This project focused on post-larval juvenile hard clams and included “outplanting” of laboratory exposed clams to grow-out sites in a New England estuary where hard clams are abundant. The study design sought to mimic short-term exposures to acidification that shellfish experience in the wild and/or during aquaculture operations. Results will be useful to water quality and shellfish managers seeking to protect bivalve resources and potentially to industry stakeholders seeking to adapt their aquaculture practices to coastal acidification.

Description:

Ocean uptake of carbon dioxide (CO2) is causing changes in carbonate chemistry that affects calcification in marine organisms. In coastal areas, this CO2¿enriched seawater mixes with waters affected by seasonal degradation of organic material loaded externally from watersheds or produced as a response to nutrient enrichment. As a result, coastal bivalves often experience strong seasonal changes in carbonate chemistry. In some cases, these changes may resemble those experienced by aquacultured bivalves during translocation activities. We mimicked these changes by exposing juvenile hard clams (500 μm, Mercenaria mercenaria) to pCO2 in laboratory upwellers at levels resembling those already reported for northeastern U.S. estuaries (mean upweller pCO2 = 773, 1274, and 1838 μatm) and then transplanting to three grow¿out sites along an expected nutrient gradient in Narragansett Bay, Rhode Island (154 bags of 100 clams). Prior to the field grow¿out, clams exposed to elevated pCO2 exhibited larger shells but lower dry weight per unit volume (dw/V). However, percent increase in dw/V was highest for this group during the 27¿day field grow¿out, suggesting that individuals with low dw/V after the laboratory treatment accelerated accumulation of dw/V when they were transferred to the bay. Treatments also appeared to affect shell mineral structure and condition of digestive diverticula. Although treatment effects diminished during the field grow¿out, clams that were preexposed for several weeks to high pCO2 would likely have been temporarily vulnerable to predation or other factors that interact with shell integrity. This would be expected to reduce population recovery from short¿term exposures to high pCO2.