Ecological Niche and Spatial Distribution Models of the Russian Sturgeon Acipenser gueldenstaedtii Brandt et Ratzeburg (1833) in the Northern Part of the Caspian Sea Based on Long-Term Monitoring Data (1992–2011) in the Summer Period

Abstract

The ecological niches (ENM) and spatial distribution (SDM) models of the Russian sturgeon Acipenser gueldenstaedtii Brandt et Ratzeburg (1833), as well as zoobenthos—the main components of this species feeding (Annelida, Mollusca and Crustacea) in the northern part of the Caspian Sea based on long-term monitoring data (1992–2011) and raster layers of the marine environment are presented. The constructed ENM using PCA within the framework of two concepts COUE and ECOUE allowed us to test the hypothesis of conservatism of ecological niches of the Russian sturgeon over time. It was shown that, while under the COUE concept the hypothesis of niche conservatism was fulfilled for one time period of monitoring, under the expanded ECOUE concept, this hypothesis is fulfilled for all monitoring periods. The SDM built by MaxEnt showed that trophic relationships between Russian sturgeon and Azov-Black Sea invaders from different taxonomic groups (Annelida, Mollusca, and Crustacea) in the northern part of the Caspian Sea are quite closely reflected in their spatial distribution. High biomass values of molluscs, crustaceans and ringworms (Annelida) as the main component in the feeding of Russian sturgeon in the western part of the Northern Caspian Sea create preferred conditions for feeding of Russian sturgeon in summer. It has been established that, in the eastern and shallow parts of the Northern Caspian the main components of the feeding are mollusks and crustaceans.