Investigating the collective effect of two ocean acidification adaptation strategies on juvenile clams (Venerupis philippinarum)

Anthropogenic CO2 emissions have altered Earth’s climate system at an unprecedented rate, causing global climate change and ocean acidification. Surface ocean pH has increased by 26% since the industrial era and is predicted to increase another 100% by 2100. Additional stress from abrupt changes in carbonate chemistry in conjunction with other natural and anthropogenic impacts may push populations over critical thresholds. Bivalves are particularly vulnerable to the impacts of acidification during early life-history stages. Two substrate additives, shell hash and macrophytes, have been proposed as potential ocean acidification adaptation strategies for bivalves but there is limited research into their effectiveness. This study uses a split plot design to examine four different combinations of the two substratum treatments on juvenile Venerupis philippinarum settlement, survival, and growth and on local water chemistry at Fidalgo Bay and Skokomish Delta, Washington. Results show no macrophyte or shell hash treatment effect on V. philippinarum settlement or survival. A significant macrophyte treatment effect was detected on clam growth, with mean length higher when macrophytes were absent regardless of the presence or absence of shell hash. Additionally, the macrophyte treatment appeared to have an opposite effect on pH than was anticipated, where pH was higher outside of macrophyte beds than inside. Although these results do not support the use of either treatment as an ocean acidification adaptation strategy, the mixed results reported in the literature for both treatments highlight the nascent nature of this research. As atmospheric CO2 concentrations continue to increase, there is an exigent need for additional studies to determine the specific conditions under which these strategies might help produce conditions conducive to settlement, growth, and survival of bivalves and other calcifying organisms. Such research could help guide local adaptation actions, especially among resource-dependent communities that rely on sustainable fisheries for their health and well-being.

Greiner C. M., 2017. Investigating the collective effect of two ocean acidification adaptation strategies on juvenile clams (Venerupis philippinarum). MA Thesis, University of Washington, 32 p. Thesis.

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