Study of Mnemiopsis leidyi density and biomass in the southern Caspian Sea
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Nasrollazadeh Saravi, H.
Keyhani Sani, A.
Kardar Rostami, M.
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AbstractComb jelly Mnemiopsis leidyi investigation was conducted in the southern region of the Iranian coast of the Caspian Sea during the 2010 in the seasons of spring, summer, autumn and winter at 8 transect with depths of 5, 10, 20, 50 and 100m. Sampling was done at 0–5, 0-10, 0-20, 20-50 and 50–1000 m using a 500 µ and 50 cm mouth opening area. During 2010, a total of 757 samples of comb jelly were collected by the size length of smaller than 5 mm to a maximum of 35 mm. Mean annually Mnemiopsis abundance and biomass was 11±2 ind.m3 and 0.6±0.1 g.m3 . Maximum abundance was recorded in autumn with 25.7±4.8 ind.m3 and maximum biomass was observed in summer of 1.2±0.1 g.m3 . Minimum abundance was found in spring with 2.3±0.4 ind.m3 and minimum biomass was in winter of 0.1±0.3 g.m3 . Statistical comparison showed that the density of comb jelly were not significantly different in spring and summer (P>0.05, Tukey test), and winter and summer with the same density, while having the highest density of autumn compared to other seasons which showed a significant difference (P<0.01, Tukey test). Comb jelly biomass showed summer and spring with higher than winter and autumn, compared to the statistical comparison showed no significant difference in biomass between seasons of summer- spring and fall – winter (P>0.05). Fluctuations of comb jelly abundance and biomass in different seasons showed that the water level of 20 m had a higher value than other layers. In the spring, more than 98 percent of the comb jelly was recorded in the upper layer (less than 20 m), and only 2 percent of the animals living in layers of 20-50 m. In the summer and autumn, about 93 percent of Mnemiopsis was found in the layers above 20 m and 7 percent of those in the lower layers (maximum 50 meters). In the winter, more comb jelly were observed in layers from 20 to 50 m (about 14 percent) and about 87 percent of them were collected in layers less than 20 meters. As a whole, the total maximum annual average abundance was recorded in the autumn of layer 0-5 m with 94.0± 33.8 ind.m3 and the highest average biomass in the 0-5 m layer of summer with 3.1±1.0 g.m3 . Frequency of group length (size) of the population M. leidyi showed that comb jellies of less than 15 mm (prior to adult) consisted of 85.8%, in which at less than 20 m, group length (size) of 15 mm included of 82-92% and at the depth of more than 50 m, these group was 8-18%. Also comb jelly adults (greater than 16 mm) in the surface layers (less than 20 m) were included of approximately 73 to 100% and below 20 m, 0-27 % of the population. Data of the 8 transect showed that the highest density and biomass of Mnemiopsis were recorded in Torkaman with 16.4± 6.5 ind.m3 , and 0.8±0.2 g.m3 , respectively. Statistical comparison of the mean abundance and biomass of comb jelly showed that there were a significant differences between Turkmen and Amirabad transect compared to other transects (P<0.05). 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. 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 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 : Nr42896;