Abundance, species diversity and structure of the metazoan microzooplankton community in the bay - seaside gradient (on the example of the Sevastopol bay)

Abstract

Comparison of metazoan microzooplankton (MM) communities in terms of abundance and species diversity in three local water areas of the Sevastopol coastal area: from the inner part of the Sevastopol Bay to the open seashore is carried out. The localization of sampling stations reflects the gradient of environmental conditions, characterized by a different degree of impact of natural and anthropogenic factors on the biota. The studies were carried out in the summer and autumn seasons. MM samples were taken from three horizons of the water column: surface, 0-5 and 0-10-meter layers. In the open seaside and the mouth of the bay, the abundance of MM along the vertical was characterized by a greater evenness, while in the depth of the bay the differences between the layers could reach 5–700 times. The maximum number of MM was observed in early August in the surface layer in the inner part of the bay - 1837.1 thousand ind. m^-3. Since the end of summer, the abundance has decreased in all the studied water areas. The species diversity of the MM community, assessed using the Shannon, Simpson, Pielu, and others indices, decreases in the direction from the open seashore into the interior of the bay. This pattern persisted in both seasons. The most informative were the Shannon index, the Simpson polydominance index and the Pielou index of evenness. They reflected well both seasonal changes in species diversity and direction of changes in the trophic gradient of the local waters of the bay. With the help of multivariate analysis, cases of significant changes in the structure of the MM community of the bottom layer of waters in the inner part of the bay were revealed. The main probable cause of these local changes is the occurrence of hypoxic conditions in the lower water horizons in the polluted areas of the bay, leading to the degradation of the abundance and species composition of the studied zooplankton community.

Keywords: metazoan microzooplankton, abundance, species diversity, community structure, bay – seaside gradient, Sevastopol Bay