CILIATED PROTOZOAN COMMUNITIES OVER COBB SEAMOUNT - INCREASE IN BIOMASS AND SPATIAL PATCHINESS

Species composition, abundance, biomass and patchiness of ciliated protozoa were examined for evidence of increasing standing stock in relation to productivity (chlorophyll a, primary production) over an eastern subarctic Pacific seamount (Cobb, 46-degrees-45' N, 130-degrees-48' W). Ciliates were unusually diverse with 49 different taxa recorded ranging in size from 15 to 350 mum in length. Their abundance was relatively low while carbon biomass was very high compared to those of most marine systems. This implies that over Cobb Seamount, ciliates counterbalance their low numbers by increasing in size, partly due to exclusion of small planktonic common species (Strobilidium spp., scuticociliates, hymenostome-type cells) by larger cells, particularly plastidic oligotrichs of the genus Laboea. Integrated biomass to 80 m depth at times peaked at 0.6 g C m-2, which exceeds the standing stock of the entire microzooplankton in some oceanic areas. Statistical 2-dimensional analysis of the spatial structure showed the existence of patchiness. Meso-scale and circular patches (about 6 km or more in diameter, horizontally) were probably related to seamount-induced physical forcing which likely generates microhabitats favorable to the growth of opportunistic or physiologically adapted populations. Direct observations showed that ciliates were a major component of the microzooplankton over the seamount.