Rotifer distributions in the coastal waters of the northeast Pacific Ocean

Abstract

Absolute abundance of rotifers was assessed from 5 to 80 km across the continental shelf off of the southern Oregon coast (U.S.A.) in the northeast Pacific Ocean. A total of 97 vertically stratified water samples were collected at 49 stations from two depths, 3 and 30 m. Coastal upwelling conditions were indicated, with decreased temperature, increased salinity and higher chlorophyll-a concentrations closer to shore. Two rotifer genera, Synchaeta and Trichocerca occurred within 16 km of shore with densities increasing closer to shore. Synchaeta reached densities of 64 inds 1−1 while Trichocerca was sparse (< l inds. 1−1). Rotifers were most abundant at 3 m and the densest aggregations appear to be associated with estuary outlets, suggesting that estuaries may be important in exporting rotifers to nearshore coastal waters.