PLANKTONIC CILIATED PROTOZOA - THEIR DISTRIBUTION AND RELATIONSHIP TO ENVIRONMENTAL VARIABLES IN A MARINE COASTAL ECOSYSTEM

The spatial distribution of planktonic ciliated protozoa, physical variables and potential food items were measured at northern and southern sites off the west coast of the South Island, New Zealand, to examine which variables were important in structuring the ciliate community. Ciliates contributed 30% of total zooplankton biomass. Ciliate abundance was greatest within 55 km of the coast on the northern transect, but on the southern transect the greatest abundance was close inshore and at the stations offshore of the continental shelf. The ciliate community was dominated by small oligotrichs and abundance (114-1139 1(-1)) was comparable with other oligotrophic marine environments. The depth of the pycnocline had a major influence on the vertical distribution of ciliates, which were closely correlated with profiles of phytoplankton biomass and picophytoplankton abundance, but not primary production. The results of this study suggest that physical factors were more important than biotic factors in influencing the distribution of protozoan ciliates. The deep mixed layer prevented the formation of deep chlorophyll a or ciliate maxima. Few studies of microzooplankton have incorporated picophytoplankton distribution, but the importance of small ciliates and picophytoplankton suggests that these groups may play a pivotal role in mediating the transfer of organic matter to higher trophic levels in this marine coastal ecosystem.