Live-Dead Shifts in Molluscan Functional Diversity in Coastal Alabama

Abiotic and biotic environmental factors shape species behavioral, physiological, and morphological traits. Shifts in the diversity of these functional traits therefore can serve as an indicator of spatial and temporal changes in environmental conditions. In recent centuries, the delivery of nutrients to coastal ecosystems has increased markedly through changing waste management and land-use practices. Nutrient enrichment has increased rates of primary productivity, resulting in greater organic accumulation on the seafloor and the development of hypoxic conditions in some areas, due to the aerobic decomposition of phytoplankton blooms. Anthropogenic eutrophication and associated hypoxia have been monitored annually in the northern Gulf of Mexico for over four decades, with an emphasis on areas surrounding the Mississippi River Delta. To further understand how anthropogenic eutrophication affects functional diversity in benthic marine communities, we collected live and dead assemblages of bivalve mollusks from surficial sediments at five stations along the -20 meters isobath in coastal Alabama. Bivalves were categorized into functional groups using information about their mobility, fixation, feeding type, substrate preference, and body size. Consistent with our hypotheses, preliminary results indicate a temporal shift from benthic communities dominated primarily by epifaunal and infaunal suspension-feeding species to communities characterized primarily by deposit feeders, many of which dwell on the seafloor surface. Ongoing analyses will help identify the functional traits that are most sensitive to these changing environmental conditions. Understanding functional diversity shifts in the recent past can provide insight into how anthropogenic eutrophication may further impact benthic marine ecosystems in the future.