Background. Studies carried out on sand littoral have shown that potentially competing species typically diverge either horizontally from shore to waterline or vertically, preferring to occupy different layers of sand or preferable food resources. The ciliates is one of the most important components of the marine interstitial space. The class Karyorelictea forms the basis of the benthic ciliates community (up to 90 % in number and biomass). We considered the conditions for the coexistence of closely related karyorelictean species on the marine littoral.
Materials and methods. Studies were conducted from May to September in 2009–2011, 2013, 2018, 2019 on the sandy littoral of the Gryaznaya bay of the Kandalaksha gulf in the White Sea. They studied seasonal population dynamics, horizontal distribution at three spatial scales, vertical distribution and infusion feeding.
Results. A total of 26 morphospecies of karyorelicteans were found in the community under study. All ciliates we studied are found throughout the summer season. The average overlapping of seasonal distributions of species is 0,31 (Bray – Curtis index). At the scale of the whole sandy beach, there is an independent distribution of closely related species. The average overlapping distribution of all species ranges from 0,19 to 0,37. The spatial distribution of the karyorelicteans over an area of 200 cm2 proved to be very homogeneous. Many abundant species have rather high similarity indexes, on average 0,79. The distribution of 20 cm2 of ciliates over an area is also very homogeneous. All abundant species have high similarity indices (0,8 on average) and are homogenously distributed at this scale. Vertical dispersion of species is very weak (average Bray – Curtis similarity index is 0,71). All ciliates preferred the layer of 0,2 cm. Our study of karyorelictids nutrition showed that they also differ significantly in food (average overlapping – 0,36).
Conclusions. Resource sharing in ciliates associations occurs, firstly, due to the discrepancy between species in time and preferred food, secondly, because of the horizontal distribution of species at a scale of tens or hundreds of meters, and only slightly at smaller horizontal and vertical scales.
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