Monitoring and rearing survey of Mnemiopsis leidyi in the southern of Caspian Sea
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AbstractWith the arrival of the invasive comb jelly Mnemiopsis leidyi in the Caspian Sea in 1991, extensive changes have been occurred. Therefore, this project aims to investigate the comb jelly M. leidyi monitoring and rearing in the southern Caspian Sea in 2013. To survey of M. leidyi and zooplankton abundance and biomass, sampling was carried out during the four seasons at spring, summer, autumn and winter in 4 half-transect (Anzali, Tonekabon, Noshar and Amirabad) and also samples for the ctenophore rearing was done at depths of 5, 10 and 20m. Sampling was performed with a 500 and 100 μ plankton net vertically at layers of 0-5, 0-10 and 0-20 m. 12 aquaria of 50 L volume were designed with salinity of the Caspian Sea to study the breeding and fecundity with aeration. 3 of aquariums with salinity of 9±1pp, 3 with 11±1ppt and 3 of 12±1 ppt filled with Caspian Sea water. Water temperature in each of the three treatments was set in 20±2oC, 23±2^oC and 25±2^oC. 3 of aquaria were set at the salinity of 12.5 ppt and at the same temperature of the Caspian Sea (20, 23, 25^oC) as control. Mean annually Mnemiopsis abundance and biomass were 16.8±1.5 ind.m^3 (139.5±41.1 ind.m^2) and 1.9±0.1 g.m^3. (5.3±0.7 g.m^2). Maximum mean abundance was recorded in autumn with 36.6.7±13.8 ind.m^3 (355.1±103.6 ind.m^2) and maximum biomass was observed in summer of 1.9±0.2 g.m^3(15.0±1.5 g.m^2). Minimum mean abundance was found in spring with 1.3±0.5 ind.m^3 and minimum biomass was in winter of 0.01±0.005 g.m^3. Regional distribution of M. leidyi in the southern Caspian Sea showed aggressive area in terms of density and biomass are areas with significant differences (P<0.05). Comb jelly population showed that both West and East in terms of abundance and biomass were similar but different with the central region. Eastern and western regions compared to the central region have the higher abundance. Laboratory studies on M. leidyi reproduction of different sizes at different temperatures showed an average of 12 eggs per day spawning. Maximum spawning rate was registered with 115 eggs per day, for M. leidyi of 46-15 mm (0/7-9/7 g) which increased with increasing size. Average M. leidyi spawning recorded in 11ppt with 25oC was twice in 12ppt (14 eggs. day-1 ) while in salinity of 12ppt of 23^oC the fecundity was two half-times in temperature of 25oC and equal of 20oC. Maximum M. leidyi fecundity was recorded at 23^oC with salinity of 12±1ppt with 22.8±35.5 eggs.day-1. There was a direct regression between size and weight fecundity of M. leidyi, in which fecundity of more than 16 mm length showed the maximum spawning. Based on the study looks at the rise and persistence parameters of comb jelly, it seems two main factors such as water temperature to the desired value, especially in summer (22-30°C), and food availability (zooplankton) have more roles in the increasing of M. leidyi the southern of the Caspian Sea. After the invasion of M. leidyi into the Caspian Sea, not only the abundance and biomass of zooplankton decreased but also the species diversity decreased from 36 to 15 species. Hence, it seems the decline in the South Caspian comb jelly was due to decreased of fecundity for lack of zooplankton feeding resources.
Publisher or UniversityIranian Fisheries Science Research Institute
Series : Nr50961;