Hypoxia and warming are associated with reductions in larval bivalve abundance in a tropical lagoon

Abstract

Hypoxia can have drastic adverse effects on coastal ecosystems, especially when coupled with heat stress. Most organisms are thought to be more sensitive to stress during their larval phase, though few studies have documented impacts of multiple stressors, like hypoxia and temperature, on invertebrates in the field or on their larvae. We measured the effects of low oxygen and warm temperatures on bivalve larval concentrations in Almirante Bay, a tropical lagoon in Panama, by collecting both plankton samples and environmental data weekly from midwater and deep water at 3 sites during 2017. For part of the year, midwater depths were cooler and more oxygenated, while deep waters were warmer and hypoxic, with more extreme and persistent hypoxia further onshore. During this warm and hypoxic season, larvae became less concentrated in deep samples at both the moderate and extreme hypoxic sites. A multiple regression, run on all deep samples regardless of site, indicated that the interaction between temperature and oxygen and the main effect of oxygen both significantly affected larval concentrations. As coastal oceans continue to warm, these relationships will likely reduce settlement and/or recruitment in hypoxia-prone areas and ultimately alter local benthic ecosystems.