| This paper mainly focused on the important bivalve Anadara broughtonii in China. The filter-feeding effect by A. broughtonii on Cylindrothecafusiformis under laboratory condition was evaluated, whilst the filter-feeding ability, functional reactive type and the effect of A. broughtonii on algae were analyzed. By investigating the food source characteristics of cultured ark shell in mariculture zone at Lingshan Bay of Qingdao, this study revealed the relationship between the phytoplankton community and food composition of A. broughtonii, through a short discussion on the seasonal shifts of diets contribution between Raft mariculture and Bottom sowing proliferation. This study aims to gain more knowledge about the feeding physiological ecology of A. broughtonii, furthermore, help to provide reference for the production and carrying capacity of cultured bivalves. The main results are as follows:1. The filter-feeding effect by A. broughtonii on C.fusiformis was studied in 20 ℃ and dark condition. The results showed that the fitted Holling disc equation was Na=1.0195×N0/1+0.002039×N0, which was able to be simulated by Holling-Ⅱ type. Based on this model the maximum number of the filter-feeding quantities for each ark shell (shell length 30-35mm) was 500×104 cells/day. The attacking coefficient tended to raise first and then declined in the range of 10-25℃ and reached peak level at 20℃, supporting that 20℃ was the most optimum feeding temperature. Besides, a strong intraspecific mutual interference was found in the filter-feeding activity of A. broughtonii. The average filter-feeding quantities of the juveniles decreased and the filter-feeding efficiency declined with increasing ark shell density, thus the model of density to C fusiformisid was E=0.7308×P-1.068. In addition, the associated response equation Na=0.7451×P-0.0684×N0/1+0.0020×N0 was built to connect the density of A. broughtonii and the concentration of C. fusiformis.2. The environmental factors and phytoplankton were monitored in raft mariculture area, Lingshan bay of Qingdao, from May 2014 to Jan.2015. The results showed that quanlity of natural seston maintained at a middle level (more than 0.30). The chlorophyll a concentration ranged from 1.35 to 6.31 mg/m3, showing a significant dual-peak feature. The primary productivity fluctuated from 93.49 to 1137.21 mgC/(m2·h), which varied differently with chl.a. Seasonal variation of phytoplankton cell abundance was evident, and we found there are 5 categories,29 classes and 48 kinds of planktons altogether, among which diatom is the major group. In summary, the biodiversity of phytoplankton in the survey area kept in a high level.The composition of three food sources (Surface particular organic matter:SPOM & Bottom particular organic matter:BPOM & Attached microalgae:AM) for the cultured A. broughtonii was estimated using stable isotopes and stomach content analysis in raft mariculture area. Research on the δ13C and δ15N characteristics of ark shell and their food resource demonstrated that they were changed significantly with the varied season. The δ13C signatures in A broughtonii mainly distributed from -19.56%o to -19.23%o, which were intermediate among those of SPOM (-23.31‰ to -21.77‰), BPOM (-22.13‰ to -21.21‰) and AM (-17.05‰ to -16.00‰). The computation by the IsoSource software was consistent with the traditional view that particulate organic matter in water column (POMs, mainly phytoplankton) is the principle food source for A. broughtonii, with the contribution about 60.0%-77.8%, and the BPOM got more contribution than SPOM. Attached microalgae on mariculture cages took up about 22.1%-40.0% contribution in diets, showed a strong resemblance to the composition of the stomach content. This results indicated A. broughtonii feed on a mixture diet of particulate organic matter and attached microalgae, and that the AM on cages can treat as important supplemental food sources in raft mariculture areas. Furthermore, stomach content analysis showed the food composition of ark shell depended on the seasonal shifts of diet in water column to some extent. Diatoms were the obviously dominant species, including Coscinodiscus, Navicula, Pleurosigma, Nitzschia and Skeletonema.3. Field study in May and Sep.2014 indicated that there were significant seasonal differences in environmental factors (i.e. natural seston quanlity, chlorophyll a and primary productivity) and phytoplankton between the two investigation sites. The dominant species were still diatoms in each site. Number of phytoplankton species in Sep. was obviously more than that in May. Additionally, there appeared differences about phytoplankton structure lined between surface and bottom water in the bottom sowing area.Stable isotope (δ13C and δ15N) analysis were conducted on A. broughtonii and their potential food sources in May and Sep. in order to reveal the influence of food sources with seasonal variations and different proliferation and culturing modes. Also, we examined the similarity between stomach contents and phytoplankton community compositions in monitoring areas. Results showed that there was a significant difference in δ13C values of A. broughtonii under these two culture modes, but no difference in δ15N was observed. Meanwhile, differences in δ13C and δ15N values of ark shell may resulted from different culture modes during the same sampling season, which may be caused by seasonal shifts of diets composition and the stable isotope of food sources. The food composition of A. broughtonii was closely related to the proliferation and culturing modes. The computation indicated that, A. broughtonii in raft mariculture area consumed 61.0%～62.9% POMs (mainly phytoplankton) and 37.2%～39.0% AM respectively. Comparatively, benthic microalgae (BM) is the most important food sources in bottom sowing area, contributing from 51.7%(May) to 72.5% (Sep.). Although the filter-feeding effect of A. broughtonii was strongly affected by the predominated diet, the main species, ie Coscinodiscus, Pleurosigma, Nitzschia and Navicula, were not siginificantly different in seasons. The similarity analysis results indicated, the Proportional Similarity (PS) between stomach content and benthic microalgae community (85.30% in May and 77.20% in Sep.) were much higher than the comparison with phytoplankton community in water column. The differences of PS can explained that A. broughtonii show certain selectivity about the easily sinking diatoms of weaker planktonic habit, and the benthic diatoms.4. The primary productivity and the weight ratio of whole shellfish and fresh tissue were monitored from May 2014 to Jan.2015. Meanwhile, some reference to the relevant documents was consulted. Nutrition dynamic model was used to estimate the carrying capacity of A. broughtonii in the mariculture zone at Lingshan Bay of Qingdao (about 0.25 million ha). The estimates showed that fluctuation of carrying capacity due to seasonal changes in primary productivity, and the average capacity was 33.91 million tons. In the actual production, more details about comprehensive filter-feeding effect of each cultured bivalve should be studied. Besides, combining with a variety of carrying capacity models for deeper evaluation still needed. |
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