Abundance and Biomass of the invasive copepod, Acartia tonsa Dana, 1849 around the fish cage culture in the southern Caspian Sea (Mazandaran-Kelarabad), Iran

The abundance and biomass of the invasive copepod, Acartia tonsa around the fish cage culture stations in the southern Caspian Sea were investigated in 2012. Sampling was conducted on a seasonally basis and at 3 stations. Station 1 at the site of the cage, station 2 at a distance of 500 meters in the west as the site of the cage control station and station 3 was chosen within 50 meters east of the location. The goal of this study was to examine the abundance and biomass of Acartia tonsa in the location of fish cages and comparison with the control station. A sample of 18083 specimens was collected. The abundance and biomass of different life stages of A. tonsa at different sites of fish cage culture were analysed. The results revealed that significant differences between abundance and biomass of A. tonsa in different life stages (p<0.05). The mean abundance and biomass were 142.38±14.83 individuals m-3 and 1.45±0.27 mg m-3, respectively. These stages of copepodite and nauplii represent 62.2% and 37.8% of total population, respectively. The minimum abundance and biomass frequency of A. tonsa was recorded in summer compared to other seasons. The results showed that abundance and biomass of nauplii were more than the copepodite; with an average of 108.8±15.6 individuals m-3 and 1.79±0.7 mg m-3 for copepodite and 213.8±189.8 individuals m-3 and 0.5±0.6 mg m-3 for nauplii. In conclusion, the abundance and biomass of calanoid copepod, A. tonsa at station 1 and station 3 were far more than the control station. These findings suggest that the accumulation of nutrients at cage sites increased available foods, leading to flourishing of A. tonsa.