The Benthic exotic species of the Black Sea: Blood cockle (Anadara inaequivalvis, Bruguiere, 1789: Bivalve) and Rapa whelk (Rapana thomasiana, Crosse, 1861: Mollusc)

Abstract

The Black Sea is in transition from a freshwater to a marine environment and has a very low biodiversity. Therefore, it appears to be particularly vulnerable and easy target for many exotic species. Anthropogenic introductions of exotic species into the Black Sea began in the 19th century, but accelerated during the second half of the century. There are about 36 kinds of introduced species in Black and Azov seas now and some of them had already severe damage to part or whole ecosystem, while some may have limited or neutral impacts. Current status of two exotic benthic species presented here: Rapa Whelk, Rapana thomasiana and blood-cockle, Anadara inaeguivalvis. Most dramatic changes to benthic ecosystem of the Black Sea has taken place after introduction of predatory gastropod Rapa whelk from Far East (Sea of Japan) to the Black Sea in 1940s and has since spread to the Aegean and Adriatic Seas. The second species blood-cockle is a filtering feeding bivalve introduced 20 years ago, but not so well-known since its invasion ability and impact on ecosystem seems to be not very devastating. Particularly rapid distribution and increased biomass of Rapa Whelk caused severe damage to narrow benthic ecosystem. It has direct (predation on bivalves) and indirect (fishing with dredges) negative impacts on the ecosystem. Annual Rapa. whelk catches from Turkey and Bulgaria reached totally 13,000 ton year-1. This study presents updated information on spatial distribution, habitats preferences, population structures, ecological and economical impacts of two exotic species; Rapa whelk and blood-cockle. © Medwell Journals, 2009.