Population dynamic and effects of the invasive species ctenophore mnemiopsis leidyi in the southern Caspian Sea
Loading...
Date
2009
Authors
Roohi, Aboulghasem
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The invasive ctenophore Mnemiopsis leidyi (Agassiz, A. 1965) which was transported from the Black Sea into Caspian at the end of 1990s has negatively affected the ecosystem of the Caspian Sea. In this study, M. leidyi population, plankton abundance, biomass and species composition and interaction between environmental and biological characteristics were evaluated in the Iranian coasts of the Caspian Sea from 2001 until 2006. The mean abundance and biomass of M. leidyi were high in the earlier period of invasion (641 - 1056 ind.m-3 and 41.5 - 44.3 g.m-3, respectively, in 2001), with highest value in September 2001 (753 ± 529 ind.m-3 and 55.1 ± 54.7 g.m-3, respectively), and minimum values in July with 283 ± 455 ind.m-3 and 13.9 ± 21.4 g.m-3, respectively. M. leidyi production started from July, reached a peak in September, extended until October, and sharply decreased in November and December (mean abundance: 232 ± 239 ind.m-3 and biomass: 13.6 ± 12.8 g.m-3). As a whole, the biomass and abundance of M. leidyi were significantly higher in the warmer months (August and September) than in the colder months (January to April) in the southern Caspian Sea. Over the whole research area, small individuals (smaller than 5 mm) and larvae of M. leidyi amounted to 85.7%, whereas those from 5 to 10 mm amounted to 6.76%. The largest individuals (greater than 50 mm) comprised only 1%; the largest individual was 70 mm in length.
A total of 18 mesozooplankton (13 species as larvae of benthic animals) and holozooplankton (4 Copepoda and 1 Cladocera) species were identified from the study area. The total number of zooplankton species found here was 50% less than a previous investigation performed in 1996 in the same region, which was before the introduction of M. leidyi. A total of 24 Cladocera, 7 Copepoda and 5 merozooplankton species reported in the previous study. Cladocera species seemed to be highly affected by the M. leidyi invasion, where only one species Podon polyphemoides remained in the monitoring stations. While Copepoda Eurytemora minor, E. grimmi, Calanipeda aquae dulcis and A. tonsa were abundant before M. leidyi invasion, only Acartia tonsa (copepodites and adults) dominated at the inshore and offshore waters after the invasion. The maximum zooplankton abundance (22088 ± 24840 ind.m-3) and biomass (64.1 ± 56.8 mg.m-3) were recorded in December 2001 and August 2004 during the study period. Overall, mean zooplankton abundance and biomass were 7015 - 11959 ind.m-3 and 32.8 - 57.6 mg.m-3, respectively, which were 2 to 5 fold less than the mean values reported in 1996. With respect to the spatial distribution of zooplankton, maximum population was observed in regions where M. leidyi biomass was low. Long-term data showed that there were more or less positive relations among M. leidyi population, their main prey organism zooplankton and some environmental factors such as temperature, salinity and nutrient concentrations.
Description
PhD
Keywords
Biological Science , Invasive species , Ctenophore mnemiopsis leidyi