Consorts of gastropod Rapana venosa (Valenciennes, 1846) in the Northern Black Sea. Part IV: Arthropoda

This article containing information about study of the taxocene Arthropoda is a continuation of the cycle describing the composition of the consortium of the invasive gastropod mollusk Rapana venosa (Valenciennes, 1846). The consortium of R. venosa is still an unaccounted component in the biocenosis structure of the Black Sea shelf. The material used and the research methods are discussed in detail in previous articles of the cycle. The purpose of this work is to describe the complex of epibiontic organisms and to compile an annotated list of Arthropoda taxa of the consortium of R. venosa. The 27 species of phylum Arthropoda found in the consortium belong to two subphyla: Chelicerata (class Arachnida) and Crustacea (classes Malacostraca and Hexanauplia). The only representative of the arachnids class (Arachnida; Acari) – Rhombognathus notops (Gosse, 1855) – was found just twice (in a single specimen in samplings of 2016 and 2017). The shell of R. venosa serves as a substrate for the development of a variety of algae – favorable habitat for the epiphyton, which causes a high number and diversity of crustaceans in this biotope. The greatest taxonomic diversity was noted for the Malacostraca class – 25 species belonging to 22 genera of 19 families. Arthropods are represented in consortium of R. venosa by two main ecological groups – sedentary and mobile epibionts. The largest species diversity of Arthropoda is inherent in free-living mobile forms (23 species). Sedentary forms, which inferior in number of species (4), dominate by quantity (86 %) and biomass (94 %). The only representative of Cirripedia – Amphibalanus improvisus (Darwin, 1854) – is the most common (53 % of the total quantity) and massive crustacean, which contributes the most significant amount to the biomass (91.8 %) of Arthropoda in the consortium. More than 50 % of the Arthropoda species in the consortium are polyphages; phytophages are 20 %; detritophages are 28 % of the total number of arthropod species. The only adult specimen of fish ectoparasites is the isopod Elaphognathia bacescoi (Kussakin, 1969) found in a consortium of sandy rapa-whelk at a depth of 8 m in the Golubaya Bay of Sevastopol. All of the 27 species of Arthropoda found are present in the consortium of the sandy R. venosa, and only 3 species are noted on the rocky rapa-whelks. The differences in the composition of the consortium of the two ecomorphs of R. venosa are mainly due to the great development of the epiphytes and the reduced dynamics of the water masses in the sandy rapa-whelk habitats in Sevastopol region. Due to their taxonomic diversity, quantity and biomass, Arthropoda are an important element of the bottom biocenosis spatially and trophically associated with individuals of the largest gastropod of the Black Sea – R. venosa.