RUI: Dissolution Mortality of Juvenile Bivalves in Coastal Marine Deposits.

Saint Joseph'S College, Standish ME

Investigators

Abstract

ABSTRACT Proposal # OCE-0622999 Despite major advances towards understanding the factors controlling invertebrate recruitment to benthic communities, many questions remain regarding causes of the extreme juvenile mortality of post-larval bivalves. It is now widely recognized that carbonate undersaturation is a common feature in temperate, coastal, organic-rich surface sediments that are dominated by deposit feeding benthos where many organisms have calcium carbonate shells. Such undersaturation may make it difficult for recently settled, juvenile bivalves to form their shell, and so shell dissolution could represent a significant source of mortality for juvenile bivalves. If true, there would be important implications for benthic community recruitment, survivorship, and the coupling between early diagenetic processes and benthic community form and function. In this research, a PI from St. Joseph's College will conduct a multi-faceted study that will: (1) determine the effect of carbonate saturation state at the sediment-water interface on recruitment and survivorship of juvenile bivalves following their transition from pediveligers to new juveniles in intertidal mud, (2) evaluate the chemical (reaction) and biotic (transport) processes that control saturation state in these same muds and, (3) develop coupled stage-based/diagenetic models of juvenile bivalve shell dissolution mortality under "scenarios" of carbonate saturation due to variability in the carbonate cycle. Studies will be conducted on the commercially valuable species Mya arenaria and Mercenaria mercenaria. Fieldwork will be conducted at two sites in Casco Bay, Gulf of Maine, that differ in their biological and diagenetic characteristics, yet both have substantial sets of Mercenaria and Mya. The field research will focus on cohort monitoring of Mya and Mercenaria and the effect of carbonate mineral saturation state on the variability in juvenile abundance. "Sediment buffering" experiments will be used to discern if CaCO3 buffering of surface sediments immediately following the set prevents undersaturation by limiting external shell dissolution of juveniles. The site comparisons will permit examination of the importance of dissolution mortality as a function of both the biotic and diagenetic setting. Sampling at low water and mid-upper intertidal heights within each site will examine variability in dissolution mortality as a function of tidal exposure. Laboratory experiments will artificially regulate surface sediment saturation state, and thus juvenile bivalve habitat, while maintaining supersaturated conditions in the overlying water. Dissolution mortality experiments will determine "threshold" saturation states below which external shell dissolution mortality occurs for specific size classes of Mercenaria and Mya (<2.0 mm). Additional laboratory experiments will determine the immediate response of bivalves to sediment surfaces of different saturation states using a combination of direct observations and flume experiments. The collective results from the field and laboratory will be used to model scenarios of dissolution mortality in both species due to anthropogenic and natural changes in carbonate cycling. Broader impacts of this study include both an extremely strong educational component and important societal benefits. Saint Joseph's College of Maine is an undergraduate institution with about 70% of women in the student body. The immersion of students into research will build on the PI's prior CAREER award and promote students attending and/or presenting research results at national/international conferences contributing as coauthors on manuscripts. Improved understanding of juvenile bivalve mortality could have important impact on management of coastal fisheries. Finally, this research would place coastal populations of juvenile bivalves into context with open ocean plankton with carbonate shells and corals that are currently expected to suffer from similar problems with shell formation and subsequent mortality.