Fluctuations in the distribution and abundance of fishes and decapod crustaceans collected by a 6 m otter trawl net from the Cooper River-Charleston Harbor estuarine system (South Carolina, USA) were examined over a 5·year sampling period. A total of 101 fish species and 41 decapod crustacean species were collected. Species richness was greatest at stations nearest the harbor mouth. Annual fluctuations in species abundance were apparently related to low bottom-water temperatures which affected year-class strength. Ten species accounted for - 90% of the total number and - 71"7. of tbe total biomass of fin fisbes collected in the estuary: Stellifer lanceolatus, Anchoa mitchilli, Micropogonias undulatus, Brevoortia Iyrannus, Leiostomus xanthurus, Symphurus plagiusa, Bairdiella chrysoura, Cynoscion regalis, Urophycis regia, and Trinectes maculatus. The decapod crustaceans Penaeus sertiferus, P. aztecus, Xiphopenaeus kroyeri, and Callinectes sapidus dominated the fin fishes in abundance but not biomass. They composed - 96"7. by number and - 97"7. by weight of the lotal decapod fauna. The biomass of fishes from this study is lower than values reported for other estuaries along tbe Atlantic coast of tbe United States. The Cooper River-Charleston Harbor estuarine system, an important nursery area for fishes and decapod crustaceans, is characterized by gradual changes in faunal assemblages and considerable overlap in spatial distributional patterns of resident and transient species. Numerically dominant species of fish and decapod crustaceans form assemblages which are spatially and temporally ubiquitous. Resident estuarine species and stenohaline marine species are more restricted in their distribution