Similar oyster reproduction across estuarine regions differing in carbonate chemistry

Abstract

Abstract In laboratory studies, shellfish larvae often respond negatively to augmented [CO2], but no prior tests have related wild bivalve larval performance and carbonate chemistry spatiotemporally. The geography of Willapa Bay (Washington, USA) naturally generates two distinct regions of carbonate chemistry where non-native Pacific oysters (Crassostrea gigas) dominate the intertidal fauna and successfully reproduce. On the river-influenced east side, pCO2 is higher and alkalinity lower, which both contribute to reduced aragonite saturation state (Ωaragonite 1.3–1.5) relative to the west side receiving low watershed inputs (Ωaragonite 1.8–1.9). pHsws is also >0.1 lower on the east vs. west sides. Despite this difference in field conditions, no biological signal related to carbonate chemistry was apparent in oyster reproduction based on coupled chemical–biological comparisons over three summers. Instead, survival was equal between the two sides of the bay, and settlement was equal or higher on the low-Ωaragonite, low-pH east side. In a temporal comparison of four larval cohorts, settlement differed by two orders of magnitude and increased with water temperature. These field data on oyster reproduction illustrate that population-level effects may not emerge in higher mean [CO2] conditions, with possible decoupling due to local adaptation, spatio-temporal heterogeneity, or higher sensitivity to other axes of environmental variability such as temperature.