Date of Award

Summer 8-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Committee Chair

Jennifer M. Walker

Committee Chair Department

Biological Sciences

Committee Member 2

Rebecca Fillmore

Committee Member 2 Department

Biological Sciences

Committee Member 3

Jake Schaefer

Committee Member 3 Department

Biological Sciences

Committee Member 4

Brian Kreiser

Committee Member 4 Department

Biological Sciences

Committee Member 5

Alan Shiller

Committee Member 5 Department

Ocean Science and Technology

Abstract

Johnson Bayou is an estuarine system located in Pass Christian, MS. Research involved a biotic and abiotic examination of Johnson Bayou, resulting in the identification of numerous species of plants and animals, including Rangia cuneata (Mactridae) and Polymesoda caroliniana (Cyrenidae), sympatric species of infaunal bivalves. Environmental factors (e.g., water temperature, salinity) were measured over three years to describe the system from an abiotic standpoint, and used in a qualitative and quantitative reproductive histological study on R. cuneata. Results revealed differences in timing of gamete production and spawning between three subpopulations of this species. Sediment samples taken from the study areas had statistically different levels of organic matter and sediment particle sizes. A laboratory-based experiment was undertaken to examine the effect of three sediment types on the number and length of burrowing events between both species of clams. It was found that the number of burrowing events and the length of burrowing events differed significantly, and the difference in length of burrowing events in silt between species was significant.

Infaunal bivalves are ecosystem engineers, capable of altering the morphology of sediment and water column via burrowing with their foot. However, little research has examined the foot morphology and ultrastructure of bivalves between sympatric species from different families. A comparative study using light and electron microscopy methods revealed that R. cuneata and P. caroliniana have the same general organization of foot tissue, with a thick internal musculature, subepithelial region, and ciliated, simple epithelium. However, the composition of glandular tissue comprising the subepithelium was different between species. While P. caroliniana produces only acidic mucopolysaccharides, R. cuneata produces both acidic and nonacidic mucopolysaccharides.

Bivalve shells provide shelter and substrate for numerous organisms and as a source of calcium and carbonate ions. Shell of either species has not been examined from a system in MS. Using microscopy methods, R. cuneata produces four shell layers, while P. caroliniana produces three. Presence of iron and titanium were detected from the periostracum, silicon and strontium in the nacre, but not from the adductor muscle scar, and the elemental composition of the outer and middle layers was the same.

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