Members of the polychaete family Nereididae do not occur naturally in the Caspian Sea but are documented intentional human introductions that commenced in 1939. However, the identity of the species involved has been uncertain; material has been identified as both Alitta succinea and Hediste diversicolor. In this study, we confirm the presence of both species in the Caspian Sea. We discuss the distribution of both species, based on tolerance to physical factors, especially salinity. Although establishment of this partially predatory Nereidid, as a food reservoir could facilitate the recreation of commercially exploited fish stock, the consequences for native benthic communities are unclear and may be subject to unforeseen negative impacts.
Seasonal and inter-annual variations in the density of the invasive polychaete Streblospio gynobranchiata were noted in the south Caspian Sea when sediment conditions were examined at five and 14 meters depths in 2005 and 2010. There was no clear trend in changing density in line one but in line two, in all seasons except summer, density of S. gynobranchiata decreased significantly. Maximum densities of 2,040 ind./m−2 and 1,013 ind./m−2 were obtained in 2005 and 2010, respectively. Although the percentage of total organic matter as a food resource increased from 2005 to 2010, the density of S. gynobranchiata decreased slightly in the same period. It seems that in this invasion phase the population of S. gynobranchiata has decreased to a balance condition. There is evidence that the changing density of this species is also being affected by other biotic/abiotic factors like intra/interspecific competitors and pollutants.
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