Seasonal and vertical distribution of the ciliated protozoa and micrometazoa in Kaštela Bay (central Adriatic)

Seasonal and vertical distribution of tintinnids, non-loricate ciliates and micrometazoa were studied in Kastela Bay (central Adriatic Sea) throughout 1995. The species composition of tintinnids and copepods were studied as well. This is the first estimation of non-loricate ciliate biomass in the coastal area of the central Adriatic. Non-loricate ciliates were quantitatively the best represented ciliated protozoa, whereas nauplii were the most numerous micrometazoan organisms. Temperature affected the distribution of most micrometazoan components of the zooplankton and that of non-loricate ciliates. The temperature-dependent presence of individual size categories of non-loricate ciliates was also established. Apart from the interaction between microzooplankton groups, the influence of biotic factors, such as phytoplankton, bacteria, non-pigmented nanoflagellates (NNF) and mesozooplankton, was also discussed. The abundance of ciliates was controlled by both food supply (phytoplankton and NNF) and micrometazoan grazing. The results point to very complex trophic relationships within the planktonic community, suggesting that microzooplankton could be an important link between the microbial food web and higher trophic levels.