A long-term (8-y) field study was made concerning the trophic relationships of fishes that occupy shallow coastal grassbeds in the northeast Gulf of Mexico. Various populatlons migrate into such areas to nursery during portions of their life histories. Many fishes undergo seasonal progressions of food preferences that follow species-specific, ontogenetic patterns. While the extent of such dietary successions varies considerably among the 14 species examined, many populations follow developmental progressions that may encompass various trophic levels from herbivory to carnivory. Omnivores are relatively common in the grassbed areas and there was a range of trophic specialization among the fishes examined. Generalized food preferences were often associated with early growth stages; as they matured, various populations became more specialized in their feeding habits Through treatment of each developmental stage of trophic preference as an individual entity (or 'ontogenetic trophic unit'), it was possible to identify progressions of feeding organization through time. Varying levels of temporal partitioning of food resources were evident. Periodic interspecific overlap of food resources was noted during periods of high productivity. Most grassbed fishes were adapted to extreme seasonal changes in habitat. This adaptation was reflected in observed temporal changes in diet and would explain the difficulty of making direct, linear associations of population distribution with multivariate analyses of specific habitat characteristics. The use of the 'ontogenetic trophic unit' facilitated the examination of the relationships of complex associations of fishes to a h~g h l y variable environment.

Epibenthic macroinvertebrate community structure (species composition, numbers of individuals and species, and relative abundance distributions) were examined at 4 study sites in the northeast Gulf of Mexico (Apalachee Bay, Florida, USA). The relative abundance distribution changes with time of sampling (diurnal or nocturnal) because individual species become more or less numerically abundant in nocturnal samples. The number of individuals collected was significantly different between diurnal and nocturnal samples at 3 of the 4 study sites. The degree of day/night variation appears to be associated with habitat complexity (as defined by plant biomass and red algae volume) for number of individuals, but not for number of species, collected. The inadequacies and consequences of reliance on an exclusively diurnal epibenthic sampling program for a good representation of macroinvertebrate community structure are discussed.

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A four-year study (1972 to 1976) was carried out to determine the long-term changes of organochlorine compound concentrations and of associations of epibenthic fishes and invertebrates in a river-dominated north Florida estuary. We assessed the relative effectiveness of a number of statistical techniques for describing the effects of key physicochemical variables on the estuarine biota. Techniques used included transformations, correlation, regression with dummy variables, two and three-way analysis of variance, multivariate analysis of variance, principal components analysis, factor analysis, canonical correlation, and cluster analysis. Several problems were encountered peculiar to studies of this type: missing observations, the sheer size of the data base in numbers of variables and observations, the domination of other effects by river flow, and extreme and noncyclical variation of some measures over the four-year study period.

Three simulated marsh systems were constructed, containing sediment, marsh plants, oysters, blue crabs, fiddler crabs, and two species of top minnows. Seawater entered each of the pools by flowing across a trough, two of which contained Mirex bait. Tidal fluctuations were simulated. Samples of water, bait, and animals were periodically analyzed. All animals concentrated Mirex. Three photoproducts accumulated on the bait particles, and both oysters and one species of fish accumulated one of the photoproducts.