Assessment of environmental variables and anthropogenic impacts on shallow marine bivalves
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Shallow marine bivalves are abundant, diverse, and typically resilient to many changes in their immediate environment. Many bivalves function by filtering ambient water (with nutrients) through their siphon and gills. This thesis addresses environmental variables and their relationships with bivalves in two very different contexts. The first chapter addresses the utility of bivalve sclerochemical data as an archive for heavy metal concentration to infer pollution in the northern Adriatic Sea, Italy. The second examines how natural abiotic factors influence community structure, body size, and predator-prey interactions of bivalves in San Salvador, Bahamas. Each study observes how bivalves live and respond to changes in environmental conditions, whether natural or anthropogenic. Heavy metals and other pollutants in the water endanger marine invertebrates, especially those that grow in equilibrium with their surroundings. Using Tapes philippinarum and Tapes decussatus we used LA-ICP-MS to analyze the concentrations of Ni, Cu, Zn, Pb, and Ba. Based on data collected, we cannot interpret ontogenetic trends of heavy metal concentration values as the literal pollution history of a location. Indeed, these records are influenced by individual growth patterns as organic content of the shell is higher during growth checks. Shells analyzed from lagoons proximal to agriculture and urban settings typically have elevated levels of heavy metals and Ba. Community dynamics and structure in an ecosystem varies based on many factors, here we investigate how salinity, sediment type, and temperature impact bivalve ecology. Abiotic factors invoke biologic responses, through body size distribution, predator-prey interactions, and spatial distribution of taxa. Salinity and sediment type have the greatest impacts on the ecology of this tidal creek, which are represented by the ecological distribution of the bivalves in this study. Using a Canonical Correspondence Analysis we quantified the relationship between the environmental parameters and the taxa. Salinity dictates variation in bivalve distributions in the creek, with areas of normal ocean salinity to containing greatest number of bivalve specimens in this study. Predation is influenced by the salinity gradient having more shells with drill holes located in areas of lower salinity.
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