| Summary |
Seasonal species composition, vertical and horizontal distribution, density, and diversity of macrobenthos were studied in the oligohaline area of the Pamlico River, an estuary in North Carolina. Samples were taken monthly from six sites located in 1 m or less of water. Salinity, temperature, dissolved oxygen levels, and sediment particle size and organic content were determined. Water temperatures ranged from 3°C during January to 31.5°C during June. Salinity of the water column ranged from 15.1°/̥ ̥ to 0.6°/̥ ̥ . Temperature and salinity of interstitial water was less than that of bottom and surface water. Dissolved oxygen of the water column ranged from 2.4 ml/L to 16.6 ml/L while interstitial values ranged from 5.4 ml/L to undetectably low levels. Sediments consisted primarily of sand particles. Mean organic content was found to be approximately 0.2% of the total dry weight. Macrobenthos were found to have low diversity and fluctuating densities. The Shannon-Weaver diversity index revealed low values of 1.24 to 2.77 and Pielou evenness values ranged from 0.05 to 0.73. Twenty four species of macroinvertebrates were identified. The majority of these organisms exhibited low densities and were transient. However, several opportunistic species exhibited large pulses in their density during various times of the year. Recruitment of juveniles during spring and fall accounted for a large portion of these high densities. The polychaetes Laeonereis culveri, Hypaniola florida, and Scolecolepides viridis and the amphipod Gamma tigrinus (group) were the primary opportunistic species encountered. Harsh environmental conditions created by changing salinity, dissolved oxygen, and unstable sediments favor such species which are adapted to exploit short term pristine environments. The macrobenthos underwent significant seasonal changes in species composition as a result of seasonal reproductive programming and changing environmental stresses. Investigation of macrophyte presence and macrobenthos densities revealed higher densities of fauna in dense macrophyte vegetation. Fifty nine percent of the invertebrates found were from sites containing vegetation. This value conceivably could have been even higher if the organisms studied had been less motile. It is believed that macrophytes play an important role in the productivity of the estuary by providing detritus for the detrital pathway, protection from predation, surface for epiphytes and epifauna, and stabilizing sediments. |
