The Bivalve Mollusc Abra ovata: Role in Succession of Soft Bottom Communities on Newly Flooded Area of the Caspian Sea

The succession of an Abra ovata community that had formed at the flooded area in Sulaksky Bay (the Caspian Sea) since the mid-1980s was investigated. The resident species Abra ovata and Cerastoderma glaucum, the pioneer settlers, were found remaining dominant in the community structure and driving the course of its succession, despite some decrease in settlement density and in the rate of occurrence. It was the tolerance of the Sulaksky pioneer settlers for later colonists (macrophytes, mytilids, crustaceans and other organisms) that determined the development of the first succession stage. The next succession stage in Abra ovata communities of Sulaksky Bay does not quite agree with the pattern typical of solid substrates. On the one hand, the community development supports the tolerance model: the pioneer Abra, in spite of being dominant through all the succession stages, does not oppose the settling of other multiple colonists; on the other hand, it agrees with a facilitation model where the abundance of the original settlers, the grazing species, provokes appearance of sturgeon.