09 Dolan (2217) (ds)

Estuaries, compared to offshore waters, are often characterized as habitats in which the biomass of aquatic organisms is high but their diversity is low. Standard reference works [e.g. (Kinne, 1971)] and textbooks on estuarine ecology [e.g. (Day et al., 1989)] present inverse relationships between species abundance and salinity, typically for benthic invertebrates. Variability of the environment in terms of salinity is the usual explanation offered, although the pattern is also found in stable systems such as the Black Sea [e.g. (Deaton and Greenberg, 1986)]. Thus, for molluscs, low estuarine diversity has been linked to physiological difficulties of osmoregulation (Gainey and Greenberg, 1977). Phytoplankton commonly appear to follow a pattern of decreases in biomass coupled with increases in diversity from low-salinity waters of 5–8‰ towards the mouth of the estuary [e.g. (Muylaert and Sabbe, 1999)]. As with benthic molluscs, low estuarine diversity of phytoplankton, compared to that of coastal marine or oceanic waters, has been attributed to extreme dominance by a few forms able to prosper in an osmotically adverse environment with otherwise favorable growth conditions [e.g. (Hulbert, 1963)]. Like phytoplankton, estuarine zooplankton communities have long been described as very abundant, but composed of few species [e.g. (Riley, 1967)]. Copepod assemblages then typically decrease in biomass and increase in diversity with salinity [e.g. (Mouny et al., 1998)]. In contrast, benthic ciliates (protists) are diverse in brackish water sediments as well as in freshwater sediments (Fenchel et al., 1997; Finlay et al., 1998). Studies of the aquatic flora and fauna of the Chesapeake are numerous [reviewed in Majumdar et al. (Majumdar et al., 1987) and Malone et al. (Malone et al., 1999)], and although none has focused on diversity among planktonic organisms, general observations suggest that a typical estuarine trend of diversity increasing with salinity is followed by phytoplankton (Sellner, 1987), mesozooplankton, especially copepods (Brownlee and Jacobs, 1987; Purcell et al., 1999), as well as among macrofauna, specifically large benthic invertebrates (Newell and Ott, 1999) and fish (Wagner, 1999). Here we explore, in some detail, the diversity of tintinnid ciliates, a