چكيده انگليسي :
Abstract:
The project investigates the relationship between the biological parameters (phytoplankton, zooplankton, Macrobenthic and the comb jelly Mnemiopsis leidyi) and environmental parameters, nutrients and environmental pollutant (oil, pesticides, heavy metals, and detergents) in water and sediment, at the southern part of Caspian Sea in 2009-2010. Sampling was performed in four seasons (spring, summer, autumn and winter) and in eight transects perpendicular to the coast in Astara, Anzali, Sefidroud, Tonekabon, Noshahr, Babolsar, Amir Abad and Turkmen. Samples were collected from depths of 5, 10, 20, 50 and 100 meters and the different layers. The relationship between biological and environmental parameters surveyed through parametric and multivariate methods.
Based on the result, the annual mean of environmental parameters and nutrients concentration at euphotic layer such as water temperature, salinity, pH, transparency, DO%, ammonium, nitrate, inorganic nitrogen (DIN), organic nitrogen (DON), inorganic phosphorus (DIP), organic phosphorus (DOP) and soluble silicon (DSi) were 17.82±0.32 (ºC), 11.35±0.10 (g/l), 8.43±0.01 (m), 126±1 (%), 3.76±0.19 (µM), 1.55±0.07 (µM), 4.81±0.13 (µM), 29.88±0.66 (µM), 0.24±0.01 (µM), 0.62±0.02 (µM), 8.22±0.22 (µM), respectively. Meanwhile, annual mean of environmental pollutant such as TPH, OCPs and LAS in water were 12.33±1.76 (µg/l), 2.85.0.90 (µg/l), 0.048±0.003 (mg/l), respectively and for TPH and OCPS in sediment were recorded 33.07±9.36 (µg/g) and 2.64±0.34 (µg/g), respectively. In addition, annual mean of heavy metals such as Ni, Hg, Pb and Cd at water were 4.01±0.01 (µg/l), 0.64±0.01 (µg/l), 15.0±0.1 (µg/l) and ND respectively, and in sediment were obtained 43.77±3.55 (µg/g), 0.13±0.29 (µg/g), 14.14±1.07 (µg/g) and 0.07±0.06 (µg/g), respectively. Abundance annual mean of biological parameters such as phytoplankton, zooplankton and M. leidyi were 143±12 (million cells/m3), 6548±700 (individuals/m3) and 86±10 (individuals /m3) respectively, and for biomass were 548±41 (mg/m3), 60±9 (mg/m3), 5.06±0.65 (g/m3). Abundance and biomass annual mean of macrobenthic were 5970±460 (individuals /m2) and 44±10 (g/m2), respectively.
The stratification of water column was strongly based on gradient of water temperature and the rule of salinity was low in this area. According to mono and multivariate statistical analysis, the southern of Caspian Sea experienced four seasons without any overlapping based on environmental parameters and nutrients. In 2009-10, the nitrogen concentration was higher than previous years and showed a decrease in the amount of inorganic phosphorus in the study area. Therefore, the system has been lead to phosphorus limitation. No limitations of the DSi in the Caspian ecosystem had caused the dominance of bacillriophyta phylum during spring, autumn and winter. However in summer (highest seasonal mean temperature) which held the most DIP, the cyanophyta was dominant phylum.
During spring and winter, the abundance of zooplankton was maximized and conversely the minimum values observed during summer and autumn with growth increasing of M. leidyi. By now, M.leidyi has been preferred the time with highest temperature or salinity during year. However with considering PCA analysis result and high ability of the organism to adaptation, the M.leidyi will probably to growth and reproduce at lower temperature and salinity than now in this area.
Result showed that during summer and autumn only abundance of two of six main zooplankton groups namely Copepoda and Cirripedia were noticeable. The other zooplankton groups were low due to high consumption by different predators or were influenced by environmental factors. The dynamics population of M.leidiy is used to consider as first explanation of the Caspian ecosystem happening, however the interaction of different factors such as temperature, salinity, nutrients and predators determine the dynamic of biological parameters.
Based on statistical analysis, feeding behavior of zooplankton species was not same in different seasons and was strongly dependent on the phytoplankton structure (species diversity and population). In other words, the classical boundary of phytoplankton species to, edible and suppressed, non-edible and unaffected and finally non-edible, enhanced species was not possible. Copepoda can act as filter-feeder and raptorial-feeder. So Copepoda compare to Cladocera (generally filter- feeder and sometimes raptorial feeder) and Rotifera (mostly suspension feeding and sometimes raptorial feeder) had more chances and opportunities for the achievement food and it support them for dominanane in all seasons.
Anthropogenic and eutrophication affect on the structure and function of plankton community and it reflected on ratio of phyto/zoo biomass. Seasonal increasing of different groups of zooplankton were done through their life cycles in 2009-10, but mostly phytoplankton abundance increased several folds than zooplankton populations. This trend made the ratio of phyto/zoo biomass at 10, 4, and14 during spring, summer and autumn, respectively. In summer, with stratification of water column and dominant of Cyanophyta, grazing pressure by herbivores zooplankton was low. However in winter due to the zooplankton population growth, the ratios reached to 11, and declined with 1.3 folds compare to autumn. Because of severe decreasing of zooplankton biomass in 2009-10 compare to years before introduction of M.leidiy in to the Caspian Sea, the ratio of phyto/zoo biomass increased from "less th@n" 5 "to more than 10"
Top-down control of zooplankton grazing on phytoplankton populations was clear in the years before the introduction of M.leidyi in to the Caspian Sea. But in 2009-10 zooplankton Shannon index reduced and phytoplankton Shannon index increased. In other word higher functional diversity at the lower trophic level (phytoplankton) increased the probability of successful defense against top-down control from zooplankton and phytoplankton abundance controled mainly by nutrients materials (down-top control).
Seasonal macrobenthos abundance showed the maximum values in summer and minimum in the cold season (winter). The polychaeta had the highest proportion of abundance compare to others main orders (oligochaeta and crustacea). The dominance of deposit feeder species of polychaeta indicates to high level of organic matter in sediment and trophic status of ecosystem. Result of CCA analysis showed that three dominant orders had different behavior respect to environmental and sediments characteristics. The oligochaeta order was directly related to sediments characteristics (TOM) and inverse relationship with environmental parameters at most seasons. In contrast, polychaeta order was linked with environmental parameters in most seasons.Crustacea order was related to the both of them. Two orders of oligochaeta and crustacea were also related directly to OCPs and inverse relationship with TPH and heavy metals. In the other words, the two orders were more affected by TPH and heavy metals in this area.
As a last point, increasing of trophic level from oligotrophic to the meso–eutrophic status, an increase of DO% from 105 percent to 120 percent, phytoplankton Shannon index increasing, zooplankton Shannon index decreasing, entrance of the potentially invasive species to the list of dominant phytoplankton species, increasing of phyto/zooplankton biomass ratio from less than 5 to more than 10 and also increasing of deposit feeder species abundance of macrobenthos are some evidences that indicate to disturbance and stress condition of the Caspian Sea
