Consorts of gastropod Rapana venosa (Valenciennes, 1846) in the Northern Black Sea. Part II: Mollusca (Polyplacophora, Bivalvia)

Abstract

The study of mollusks-symbionts of the predatory gastropod Rapana venosa is a continuation of the work on the description of the taxonomic composition of the epibiont complex formed on the shell of the rapana. Modern studies of invasive gastropods R. venosa show that the ecological role of this species is not reduced only to predation. On a fairly large rapana shell a specific complex of organisms-epibionts considered as a consortium can be formed, the core of which is R. venosa. The consort of the gastropod mollusk-invader R. venosa is poorly understood and unaccounted for link in benthic communities and the ecosystem of the Black Sea shelf. In order to study the rapana consortian community, sampling were conducted in 7 regions of the Northern part of the Black Sea: 1 – Mamaya, Romania; 2 – the north-western part of the Black Sea, Crimean sector; 3 – Sevastopol, 4 – Alupka, 5 – Yalta – Alushta, 6 – Karadag, 7 – Kerch Strait. The sampling of R. venosa in the coastal zone to a depth of 15 m was carried out with the use of light-diving equipment, while in the deeper zone (up to 40 m), the “Ocean-50” bottom grab was used on board of the RV “Professor Vodyanitsky”. The collection of specimens was carried out totally, each sample was placed in a separate plastic bag indicating the collection region, depth and biotope. Along with the collection of mollusks, visual observations and photographic fixation of hydrobionts in situ were carried out. A total 890 specimens of R. venosa were sampled and analyzed. Compared with previous studies, the taxonomic list of consonant mollusks of R. venosa has been significantly expanded. The mollusc-consorts found on rapana have been classified into three classes: Polyplacophora, Bivalvia, Gastropoda. In this part of the investigation Polyplacophora, presented in a consortium of 3 species of 2 genera of 2 families, and Bivalvia, 7 species of 7 genera of 5 families, were considered. It was found that mollusks are an important component of the consortium of rapana. On rocky rapana ecomorph chitons were observed at a frequency of up to 25 %, on sandy rapana — up to 10 %, in the consortium of rapans as a whole chitons were found in around 12 % frequency. More than 80 % of the all chitons total number on rapana is in Lepidochitona cinerea. The occurrence of Bivalvia in most of the investigated regions is 50–75 %. The area of covering the shell of rapana with bivalves is usually 2–20 %, sometimes reaching 85 %. The most common species of bivalves and mollusks as a whole in the consortium of the Black Sea rapana is the Mytilaster lineatus. Most Bivalvia have a close relationship with the core of the consortium attaching to the surface of the shell of the rapana, and at the earliest stages and to the surface of the epiphytes. Representatives of Polyplacophora are confined mainly to the rocky form of rapana, while Bivalvia show a greater species diversity in the consociation of the ecomorph R. venosa of loose grounds (6 species) than the rocky form (3 species). Differences in the taxonomic composition of epibionts and the percent coverage of the shell of the two ecoforms of R. venosa are predominantly determined by specific dynamic impact of the water mass in the zones of development of rocky and loose grounds.

Keywords: consortium, ecology, epibionts, Mollusca, Polyplacophora, Bivalvia, Black Sea