Space-time variation of ciliates related to environmental factors in 15 nearshore stations of the Gulf of Gabes (Tunisia, Eastern Mediterranean Sea)

Abstract

Diversity and structure of ciliate communities in the Gulf of Gabes (Tunisia) were investigated based on a survey of 15 nearshore stations along 237 Km, by monthly sampling over a year. Ciliated protozoa were identified to genus and/or species level and enumerated. Statistic tools were used to explain ciliate assemblage. High ciliate species richness from 63 taxa was recorded, including new records of several species. This study showed a longitudinal distribution of ciliate communities, which are organized at northern (from Tabia to Port of Gabes) and southern stations (from Zarrat to Jabiat Haj Ali). The number of taxa increased signifificantly at northern stations but decreased at the southern ones. This distribution was mainly influenced by salinity and phytoplankton abundance. Ciliate taxa were grouped into fifive size-classes: 15-30 μm, 30-50 μm, 50-100 μm, 100-200 μm and >200 μm. In terms of abundance, most abundant size groups were small ciliates (15-30 μm), accounting for 15 to 79 %, while the greatest biomass contribution came from the 50-100 μm size classes. Thus, we conclude that there is a high diversity of ciliate communities with a geographical distribution that is influenced by abiotic and biotic factors along the coast of the Gulf of Gabes.