Spatial and temporal variations in stable isotope values (δ13C and δ15N) of the primary and secondary consumers along the southern coastline of the Caspian Sea

Abstract

Spatial and temporal variations in stable isotope values of the coastal communities in the Caspian Sea remain poorly understood. We followed carbon stable isotope ratios (δ13C) and nitrogen stable isotope ratios (δ15N) of primary (gammarids) and secondary (common carp) consumers at four sites with different organic matter loadings along the southern coastline of the Caspian Sea from May to November 2019. Consumers from the site receiving higher sewage effluent and aquaculture wastes were more enriched in δ15N whereas those from the site receiving lower terrestrial-derived organic matter had enriched δ13C values. Trophic position of consumers varied among sites as a function of organic matter inputs but was independent of month. The observed temporal and spatial variations in the stable isotope values and C:N ratios of the primary and secondary consumers with regards to organic matter loadings, suggesting a possible effect of anthropogenic disturbance on the Caspian Sea ecosystem function.