Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Epibenthic (trawlable) macrofauna and hydrographic variables were sampled at ten stations in the Calcasieu estuary, Louisiana, from June, 1974, through February, 1976. The 100 otter trawl samples collected contained 32,221 individuals belonging to 63 invertebrate and 68 fish species. The 10 most abundant fish and invertebrate species represented 95.3 and 90.0%, respectively, of the total number of individuals collected. Seasonal variation in numbers of species and individuals were similar, with significant increases in number of species during spring and early summer months. Numerical classification was used to analyze spatial and temporal patterns of utilization of the estuary and to examine correlates of demographical variation and assemblage structure. Eight site groups and seven species groups were allocated by normal and inverse analyses, respectively. Four of the site groups were seasonally restricted, two were habitat restricted and two were both habitat and seasonally restricted. Nodal analyses identified patterns of constancy and fidelity, with spatial and temporal partitioning of the estuary by the species groups. Biotic interactions were implied by separation of congeners or closely related species into different species groups having separate centers of distribution. Diversity and evenness values, although not utile in assessing areal and seasonal patterns of fluctuations in assemblages, did delimit structural differences in closely related species groups. A relatively straight, deep ship channel extended the length of the estuary and had a dominant influence on hydrography by permitting intrusion of high salinity water. A salt water wedge, often with distinct haloclines and thermoclines, was observed at all channel stations. Salinities varied from 0.8 to 33.0('o)/oo and temperature ranged from 9.5 to 32.7(DEGREES)C in the estuary over the duration of the study. Tidal movements and seasonal variations in river discharge rates caused large temporal variations in salinity and temperature at each station. Percent oxygen saturation of channel bottom waters was inversely related to the distance from the mouth of the estuary. Percent oxygen saturation of the channel during summer months was significantly lower than the rest of the year. Hypoxic conditions of deeper stations during warmer months resulted in defaunation.