ECOLOGY OF EELGRASS, ZOSTERA-MARINA-(L), FISH COMMUNITIES .1. STRUCTURAL-ANALYSIS

Fish populations utilizing eelgrass, Z. marina, beds in 2 different estuarine areas near Beaufort, North Carolina [USA] were analyzed and compared to determine aspects of their community structure. The fish community of the eelgrass beds was characterized by low diveristy and high standing crops of biomass and energy, both of which showed seasonal variation. Wide temperature fluctuations related to the overall shallowness of the beds probably regulated the diversity of fishes utilizing the beds. This community was dominated by pinfish, Lagodon rhombiodes (L.), which comprised 45% and 67% of the fish biomass in the Phillips Island and Bogue Sound beds, respectively. Changes in total body caloric content were probably related to developmental stages and changes in diet. Adult fish often had significantly higher weight-specific caloric contents than juvenile fish. Monthly or seasonal variations in caloric content of the organic matter of pinfish had little influence on the caloric content within the various sizes of pinfish. There was a significant correlation between fish biomass, temperature and Zostera biomass. Fish biomass was highest when temperature and grass biomass were at a maximum. In general, water depth over the beds had little effect on the standing crop of fish within the bed, but cooler waters which occurred at night, in darkness, or both, had a large effect.