Studies On Ecology And The Genetic Diversity Of Dominant Species Of Macrozoobenthos In Nanhu Lake, Wuhan

Most of lakes, in the middle and later reachs of the Yangtze River basin, were faced the water eutrophicated, bio-diversity decreased and eco-function degenerated, which impaired the continuance development of laky economy severely. Macrozoobenthos is an important components of lake ecosystem and play multiple functions in aqutic ecosystem. However, the natural resources of macrozoobenthos decreased gradually for the destruction of aquatic ecosystem environment. The researches on macrozoobenthos ecology were rather less. No report of the genetic diversity of aquatic oligochaeta and insecta was found in China. It is necessary to study the ecology of macrozoobenthos and the genetic diversity of aquatic oligochaeta and insecta, because the result will help people find out the characters of macrozoobenthos community in the lake under of anthropogenic activity, and provide the theoretical basis for solving the problem of lake eutrophication and the continuous development of fisheries. The result will also benefit to the resource protection and the study of molecular phylogenetic relationship of macrozoobenthos.Therefore, the basic situation of eutrophicated shallow lake (Nanhu Lake), in the middle reaches of the Yangtze River basin, had been investigated, the communities structure and the impaction of environmental deterioration of macrozoobenthos had been analyzed, and the secondary production of macrozoobenthos had been calculated. RAPD makers was used to detect genetic diversity of five dominant species. The main results are as following:1. The physical and chemical indices of the water were measured in Nanhu Lake. The results show: The annual average water depth, water temperature and Secchi Degree of ten sampling stations in the lake were 2.31 m, 17.97 ℃ and 33.6 cm, respectively. Mean value of pH was 8.25; the average content of DO was 8.17 mg/L; conductivity was 393.44μs/cm. The mean concentration of NH₄⁺-N, NO₃^--N, NO₂^--N and TN were 3.603 mg/L, 2.072 mg/L, 0.155 mg/L, and 7.033 mg/L, respectively. The content of PO₄^3--P and TP averaged 0.184 mg/L and 0.761 mg/L, respectively. The N:P ratio was 9.357. Sixty-six species of phytoplankton were found, and its density and biomass were 2.489 ×10⁶ ind/L and 7.94 mg/L, respectively. Fifty-six species of zooplankton were found, and its density and biomass were 26285 ind/L and 3.46 mg/L, respectively. The content of TN and TP in sediment were 4.765‰ and 0.528‰, respectively. Nanhu Lake was hypereutrophicaccording to the nutritional indices of the water.2. A total of 30 macrozoobenthos taxa were recorded in Nanhu Lake, including 10 species of oligochaeta. 4 species of molluscat 14 species of aquatic insecta, 1 species of hirudinea and 1 species of decapoda. There were only oligochaeta and insecta found in the quantitative investigation of macrozoobenthos. The abundance of oligochaeta was 3381 ind/m2 and ranged from 1606 ind/m2 to 6134 ind/m2, the biomass was 9.70 g/m2 and ranged from 2.67 g/m2 to 26.64 g/m2. The seasonal variation of abundance of oligochaeta was that in Spring > Summer > Autumn > Winter, and the biomass variation was in Spring > Summer > Winter> Autumn. The abundance of insecta was 1056 ind/m2 and ranged from 918 ind/m2 to 1178 ind/m2, and had no distinct difference among seasons. The biomass of insecta was 8.09 g/m2 and ranged from 4.68 g/m2 to 13.26 g/m2and the highest in spring. The deterioration of aquatic environment resulted in the great changes of macrozoobenthos communities structure. The chironomidae groups decreased from 15 species at 16 years ago to 9 species now. Oligochaeta was mainly composed of polluted species, and mollusca was scarce. The diversity of macrozoobenthos was rather low.3. The dominant species of macrozoobenthos was Limnodrilus hoffmeisteri, Branchiura sowerbyi, Tanypus punctipennis, Propsilocerus akamusi and Chironomus semireductus in Nanhu Lake. The distribution of former four species was congregated significantly. Five dominant species were fixed with different preservation solutions, the result show: L. hoffmeisteri, B. sowerbyi, T. punctipennis and C. semireductus were suitable fixed in 8% formaldehyde solution. P. akamusi could be preservated in 8% formaldehyde solution, or in 75% ethanol, or in 75% ethanol after fixed 24 hours in 8% formaldehyde solution, but the effect was the best in 8% formaldehyde solution.4. Annual secondary production of dominant groups of macrozoobenthos in Nanhu Lake were estimated from field data. The annual P/B coefficient and production (wet weight) of five dominant species were as follow: L hoffmeisteri, 72.691 gm^yr*1, 8.74; B. sowerbyi, 5.191 gm"2yr'\ 4.82; T. punctipennis, 6.184 gm"2yr'\ 3.77; P. akamusi, 6.184 gm^yr'1, 2.70; C. semireductus, 2.625 gm'^yr'1. The production of total macrozoobenthos was 109.718 gm^yr'^wet weight), or 20.784 gm"2yr"x (dry weight), and the energy reserves was 110.6 Kcal m^-yr'1. The fishery production of macrozoobenthos was 6.588 g-m'^yr'1 in Nanhu Lake.5. The genomic DNA of C. semireductus and B. sowerbyi were used as template DNA to optimize the RAPD-PCR reaction conditions for chironomidae and tubificidae groups, respectively. For a 25 ^L reaction system, the optimized reaction systems ofRAPD amplification for chironomidae group were as follow: the optimal condition included 10 X Reaction Buffer 2.5 juh, 2.0 mmol/L MgCl2,0.2 mmol/L dNTPs, 1.5U Taq DNA polymerase, 30 ng template DNA, 0.2 pimolfL random primer. The optimized reaction systems of RAPD amplification for tubificidae group were: the optimal condition included 10 X Reaction Buffer 2.5 fiL, 2.5 mmol/L MgCl2,0.2 mmol/L dNTPs, 1.0U Taq DNA polymerase, 30 ng template DNA, 0.3 (xmoVh random primer. The optimal program for efficient amplification included 45 cycles of denaturation at 94 °C for 1 min (94 °C for 5 min for the first cycle), annealing at 37 ^C for 1 minute, and extension at 72 °C for 2 minutes (10 minutes for the final cycle), then the last products were stored at 4"C.6. Random amplified polymorphic DNA (RAPD) markers was used to detect genetic diversity of five dominant populations of macrozoobenthos. Sixteen random primers were used for the RAPD of chironomidae groups, and eighteen for tubificidae groups. The results were: the percent of amplified polymorphic bands of T. punctipennis, P. akamusi, C. semireductus, L koffmeisteri and B. sowerbyi were 41.03%, 44.0%, 41.79%, 46.01%, and 51.20%, respectively. Shannon genetic diversity of their intra-populations were 0.2570, 0.2472, 0.1943, 0.3153, and 0.3355, respectively. The intra-populations genetic similarity of them were 0.8730,0.8731,0.9066,0.8285, and 0.8310.