Estuarine diversity of tintinnids (planktonic ciliates)

In Chesapeake Bay, a large eutrophic and partially stratified estuary, we i nvestigated diversity among tintinnids (Ciliophora, suborder Tintinninia) i n September 1999. In contrast with the typical estuarine pattern, tintinnid diversity was high and increased with decreasing salinity from the mouth o f the bay to the mid-bay region. Peak species numbers and diversity values [20-25 species, H ' (ln) = 2.4-2.5] were found in stations in the mesohalin e (14-17%) portion of the bay. Within the bay, diversity was not correlated with abundance or food levels, as measured by chlorophyll fluorescence, no r with predator (copepod) concentration. However because high copepod conce ntrations corresponded to the less diverse southern bay populations, we exa mined the influence of copepods on tintinnid diversity in two field experim ents using natural populations and a size:fractionation approach. Similar c opepod predation rates on abundant tintinnid species (0.4-1 ml cleared cope pod(-1) h(-1)) were found in the experiments, but with distinct impacts on tintinnid diversify. In a slow-growing community of tintinnids, copepod pre dation decreased diversity relative to changes in communities without copep ods, while in a community highly dominated by a rapidly growing tintinnid s pecies, copepod predation increased diversity. Our results show that not al l taxa found in estuaries are species poor, and in the highly dynamic plank ton the relative influence of factors influencing diversity may change rapi dly. Species richness in the Chesapeake Bay appears predictable from latitu de.