Seasonal distribution of the ciliated protozoa in Kaštela Bay

Abstract

Seasonal distribution of the ciliated protozoa was studied in the west part of Kaštela Bay during 1995. These are the first data of the annual distribution of four size categories of non-loricate ciliates and tintinnines in the coastal area of the central Adriatic Sea. The maximum densities of ciliated protozoa were recorded during the spring and autumn, when they could act as important factors of ‘top-down’ control. Contributions of non-loricate ciliates and tintinnines to the total of ciliated protozoa were 72 and 28%, respectively. The highest density of non-loricate ciliates was registered at the surface in September (1400 ind l⁻¹). Annual variability of the non-loricates density was mostly influenced by changes in numbers of the second (10³–10⁴ μm³) and third (10⁴–10⁵ μm³) size categories and they constituted 86% of the total non-loricate counts. Non-loricates with biovolume <10³ μm³ were the most abundant during the colder part of the year while those with biovolume >10⁵ μm³ dominated during the summer. The highest density of tintinnines (718 ind l⁻¹) was recorded at 5-m depth in May. Quantitatively, the most important tintinnin species was Helicostomella subulata. The results suggest a complex influence of biotic and abiotic factors on the annual distribution of ciliated protozoa.