Effects of pH, eelgrass, and settlement substrate on the growth of juvenile magallana (crassostrea) gigas, a commercially important oyster species

• Main Author: Roche, Johnny S.
• Format: Text
• Language: unknown
• Published: Digital Commons @ Cal Poly Humboldt 2023
• Subjects: Pacific oyster; Zostera; Eelgrass; Seagrass; Crassostrea gigas; Magallana gigas; Ocean acidification; Substrate; pH; Laboratory and Basic Science Research; Marine Biology; Other Ecology and Evolutionary Biology; Pacific
• Online Access: https://digitalcommons.humboldt.edu/etd/632; https://digitalcommons.humboldt.edu/context/etd/article/1697/viewcontent/auto_convert.pdf

Worsening ocean acidification (OA), resulting from ongoing absorption of atmospheric carbon dioxide (CO2) by the oceans, threatens marine life globally. Calcifying organisms, especially their early life stages, are particularly vulnerable; this includes the economically important Pacific oyster, Magallana (Crassostrea) gigas. Uptake of dissolved CO2 through photosynthesis by seagrasses, like eelgrass (Zostera marina), may benefit calcifying organisms by increasing pH and carbonate availability. I conducted laboratory and field experiments to quantify carbonate chemistry modification by eelgrass and potential mitigation of OA impacts on growth in juvenile Pacific oysters. In the laboratory experiment, daytime net photosynthesis by eelgrass increased seawater pH, while nighttime net respiration reduced pH though to a lesser extent; both effects grew stronger as the pH of incoming seawater decreased. This is consistent with the expectation that eelgrass will benefit from increased aqueous CO2 levels and suggests that the importance of carbonate chemistry modification by eelgrass and its role as a refugium may increase as OA proceeds. Under the conditions tested, however, eelgrass effects on pH were modest and did not affect oyster growth in the lab or field. In the lab, oysters settled on shell flour grew faster than those on shell chunks, but unlike those on chunks, the growth rate of oysters on flour decreased significantly in low pH treatments. One hypothesis consistent with these results is that the boundary layer around shell chunks may have slowed oyster growth by limiting food availability but that it also reduced sensitivity to low pH via enhanced carbonate saturation.