Spatial and temporal variability in abundance and biomass of oligotrich ciliates in Kaštela Bay (middle Adriatic Sea)

Abstract

        The nonloricate ciliate (NLC) community was investigated in Kaštela Bay from January 1998 until November 1999. Samples were collected at four sites characterized by different trophic states. Cell abundance, carbon content, and size categories of the oligotrich ciliates were investigated. NLC abundance was highest in spring with average values of 400-608 ind.l^-1. Abundance during the second highest period, autumn-winter, was less pronounced. In the eutrophicated part of the bay, conditions were most favorable for NLC proliferation in summer, with the highest average density (1430±1348 ind.l^-1) in August 1998. The size structure of the NLC populations changed with the trophic gradient. Organisms of <10⁴ μm³ were useful in distinguishing trophic conditions in the marine ecosystem. Eutrophication favored growth of organisms of <10⁴ μm³ while the succession of NLC categories changed without a clear seasonal pattern. Eutrophication also increased NLC biomass and affected seasonal fluctuations of biomass values. Average monthly biomass values ranged from 0.012±0.014 to 3.925±5.094 μgC l^-1. The high abundance and biomass in Kaštela Bay suggest that NLC play a critical role in the secondary production of the area.