Estuarine diversity of tintinnids (planktonic ciliates)

Abstract

In Chesapeake Bay, a large eutrophic and partially stratified estuary, we investigated diversity among tintinnids (Ciliophora, suborder Tintinninia) in September 1999. In contrast with the typical estuarine pattern, tintinnid diversity was high and increased with decreasing salinity from the mouth of the bay to the mid-bay region. Peak species numbers and diversity values [20-25 species, H′ (In)=2.4-2.5] were found in stations in the mesohaline (14-17‰) portion of the bay. Within the bay, diversity was not correlated with abundance or food levels, as measured by chlorophyll fluorescence, nor with predator (copepod) concentration. However, because high copepod concentrations corresponded to the less diverse southern bay populations, we examined the influence of copepods on tintinnid diversity in two field experiments using natural populations and a size-fractionation approach. Similar copepod predation rates on abundant tintinnid species (0.4-1 ml cleared copepod-1 h-1) were found in the experiments, but with distinct impacts on tintinnid diversity. In a slow-growing community of tintinnids, copepod predation decreased diversity relative to changes in communities without copepods, while in a community highly dominated by a rapidly growing tintinnid species, copepod predation increased diversity. Our results show that not all taxa found in estuaries are species poor, and in the highly dynamic plankton the relative influence of factors influencing diversity may change rapidly. Species richness in the Chesapeake Bay appears predictable from latitude.