Consorts of gastropod Rapana venosa (Valenciennes, 1846) in the Northern Black Sea. Part III: Mollusca (Gastropoda)

Abstract

This work is a continuation of a series of descriptions of the taxonomic composition of the consort community of Rapana venosa. The shell of the large invasive gastropod R. venosa, which occupies the ecological niche of the terminal predator in benthic community, is simultaneously an attractive substrate for various hydrobionts – fouling and associated mobile forms, one of which is small gastropod mollusks. The latter are poorly explored and accounted for in the R. venosa consortium. The study of this group of hydrobionts in the composition of epibionts of rapana was carried out on the material obtained in 7 regions of the northern part of the Black Sea: 1 – Mamaya, coast of Romania; 2 – NW Crimean coast, Tarkhankut area; 3 – SW coast of Crimea, Sevastopol; 4 – Southern coast of Crimea, Alupka; 5 – Southern coast of Crimea, Yalta – Alushta; 6 – SE coast of Crimea, Karadag; 7 – Kerch Strait. Sampling of rapa-whelk in the coastal zone up to a depth of 15 m was carried out using light water diving equipment, in the deeper zone (up to 40 m), the “Ocean-50” bottom grabber was used from the board of the RV “Professor Vodyanitsky”. Gastropods as consorts of rapa-whelk were found predominantly in reg. 3, where in the summer – autumn season 2015–2017 the most detailed works were carried out and about 90 % of the material was sampled (1100 of 1216 R. venosa specimens). It was found that gastropods in the consortia of rapana were represented by 14 species of 9 genera of 6 families, 7 species of them with egg laying. The gastropods were observed in the consortium of R. venosa mainly in the epiphyton community of algal fouling of the shell, where the mollusc-consorts can form significant clusters – more than 60 individuals. Directly on the shell of the rapa-whelk, the gastropods were found singly or in small groups – from 2–5 to 10 individuals. The most numerous and often occurring (up to 25 %) gastropod species in the consortium of R. venosa was Bittium reticulatum (Cerithiidae). Less numerous were Tricolia pullus (Phasianellidae) (5–10 %, in Kazachya Bay – up to 25 %) and Rissoa splendida (Rissoidae) (the occurrence on the average was about 10 %). The remaining species were observed singly. The highest species diversity and abundance of gastropods were recorded at the depth of 4–10 m in the consortium of loose soils R. venosa ecomorph – 14 species; on the rocky ecomorph of rapa-whelk inhabiting the zone of more intensive hydrodynamics – only 2 species. Our research demonstrates that the ecological role of the invasive species of the Black Sea fauna, R. venosa, is not limited to be a predation. In particular, it contributes to reproduction, development and resettlement of other gastropod species. In the biotope of loose soils, where the there is a deficit of the solid substrate necessary for reproduction of many species of hydrobionts, including gastropods, R. venosa is “oasis” increasing the biological diversity of the benthos as a whole.