GUILDS OF CILIATE MICROZOOPLANKTON IN THE CHESAPEAKE BAY

The composition and abundance of three major guilds, or different trophic groups, of ciliates are reported for the Chesapeake Bay. Ciliates were classified either (a) macrophagous (consumers of nanoplankton-size or larger prey), (b) microphagous (consumers of picoplankton-size prey), or (c) predatory (consumers of other ciliates). The three guilds show seasonal changes in species composition and distinct abundance trends, based on samples taken from April to October, 1985-1987. Macrophagous forms (mostly tintinnids and large oligotrichs) represent, on average, c. 73% of ciliate biomass. However, microphagous species (largely scuticociliates and small oligotrichs) are dominant in terms of cell numbers and often form a substantial portion of the ciliate biomass in deep waters; they probably account for c. 15% of total protozooplankton grazing pressure on bacteria in the Chesapeake Bay. Predatory ciliates, while numerically a minor component of total ciliate numbers, were correlated with microphagous ciliate biomass and may, at times, have had a major impact on the microphagous guild. © 1991.