| Abstract: | The purpose of this study was to determine the composition of the associated fauna of Delaware's oyster beds. Moreover the relative position of Delaware's oyster producing tributaries lends itself to testing the classic hypothesis concerning the effect of salinity on faunal distribution. Interaction of substrate was also studied. The local oyster beds are termed the bay beds which include planted and natural populations, and the river beds. From 1967 to 1971 approximately 800 samples have been collected and the majority of these were from the bay beds. In 1968 and 1969, 132 samples were systematically collected from the river beds and 19 from the bay beds. These were returned to the laboratory for special care in identification. Samples from fouling panels and oyster rafts provided additional species. 152 species were identified but only 133 species were statistically analysed because they were from the systematic collections. Nonparametric statistics were used. In order to facilitate analysis the top 23 species were selected for special treatment. In order of decreasing frequency of occurrence the species were: Sabellaria vulgaris, Conopeum tenuissimum, Panopeus herbsti, Nereis succinea, Palaemonetes vulgaris, Crassostrea virginica, Nassarius obsoletus, Polydora websteri, Membranipora tenuis, Garveia fransiscana, Bulanus improvisus, Diadumene leucolena, Aiptasiomorpha luciae, Melita nitida, Obelia longicyatha, Alcyonidium polyoum, Sertularia argentea, Crangon septemspinosa, Hydroides dianthus, Eurypanopeus depressus, Modiolus demissus, Parapleustes sp., and Hartlaubella gelatinosa. The diversity of species decreases up the estuary with decreasing salinity. Substrate can alter this pattern in particular cases. Within a given salinity range the presence of any firm substrate or mud influenced the nature of the community from epifaunal to infaunal. Four faunal units were recognized: the planted and natural beds, the four southern rivers, the Leipsic River, the Woodland Beach area. The Leipsic River area marks a critical transition zone with a rapid reduction in species. North of Woodland Beach brackish water conditions begin to prevail. The fauna was more diverse in late spring than in the fall but seasonality was not as marked as expected. The faunal composition of Delaware's oyster beds agrees with the cosmopolitan view of estuaries. The stability — time hypothesis proposed by SANDERS provides a theoretical basis to explain faunal distributions in Delaware's oyster community. The hardy nature and geologic history of this oyster community makes it a likely candidate as a sensitive indicator of environmental degradation in the estuary. |
