贝类营养研究进展_

与鱼虾营养相比,贝类营养研究起步较晚,而且进展较慢,这主要是由于大多数贝类经济价值相对要低一些,不足以引起研究者和养殖者的兴趣;另一方面,贝类主要是以藻类为食,在现有的生态条件和养殖模式下,饵料缺乏问题尚不严重。然而在贝类中也不乏经济价值相当高的种类,如鲍鱼,而且从长远观点看,随着集约化养殖的推广,天然饵料肯定不能满足需要,用人工饲料部分或全部替代天然饵料势在必行。不少学者已在贝类营养需求以及营养学因素对贝类繁殖力、孵化率、幼体生长的影响等方面做了大量的工作。1　蛋白质1.1　蛋白质的生理功能贝类同其它动物一样,…     

Possible cytotoxic effects of the dinoflagellate, Gyrodinium aureolum, on juvenile bivalve molluscs

Juveniles of eight commercially important species of bivalve molluscs (Spisula solidissima, Argopecten irradians, Crassostrea virginica, Mytilus edulis, Mya arenaria, Ostrea edulis, Mercenaria mercenaria, Placopecten magellanicus) were exposed in the laboratory to the commonly occurring dinoflagellate, Gyrodinium aureolum. Histological analyses of gut tissues indicated that the impact of G. aureolum on the shellfish was species-specific. High rates of mortality were noted in the bay scallop, A. irradians, but not in other molluscan species. There were no pathological differences between control animals and animals fed G. aureolum in S. solidissima, M. arenaria, or M. mercenaria. The most severely affected molluscs were C. virginica and A. irradians. C. virginica did not exhibit differences in digestive gland parameters between control and experimental animals; however, several animals did show significant mantle and gill lesions. Bay scallops exhibited decreased height of absorptive cells and increased lumen diameter after exposure to Gyrodinium suggesting, at least, poor food quality of Gyrodinium. Evidence of toxic effects was not identified in the digestive gland. Several bay scallops also showed variable amounts of inflammation in the kidney associated with protozoal infestations and variable amounts of predominately rod-shaped bacteria within the urinary space. Aquaculturists, especially of scallop species, should monitor for the presence of G. aureolum. Given its large size (25-30 m), G. aureolum could be filtered from incoming water to hatcheries, thus avoiding mass mortalities of spat and juvenile scallops.     

The distribution of three uncommon freshwater gastropods in the drainage ditches of British grazing marshes

Marshland drainage channels (=ditches) in the UK are relicts of a once extensive habitat whose management requires quantitative information on the ecology of marshland organisms. Three freshwater gastropods in the UK Red Data Book (RDB), Segmentina nitida, Anisus vorticulus and Valvata macrostoma, are particularly poorly known, and we examined their macro-distribution across 106 ditches on four grazing marshes in SE England. Distribution reflected natural water quality, vegetation and anthropogenic factors. S. nitida occupied shallow calcareous ditches with dense emergent vegetation while A. vorticulus occupied less calcareous ditches with high plant diversity. Ditches with V. macrostoma were dominated by floating plants and slightly elevated chloride. S. nitida and V. macrostoma were absent from otherwise suitable ditches that had elevated nitrate and nitrite indicating effects from eutrophication. Conservation of these three gastropods at the regional scale requires reductions in catchment fertiliser use and also the protection of enough sites to provide the required range of natural factors (e.g., Cl and Ca). At the marsh scale, we suggest that quasi-traditional and rotational ditch clearance can provide the vegetation dynamics and diverse ditch network to ensure suitable habitat for all three species. Better information is required about dispersal, about the effectiveness of reintroduction, and about the most sensitive methods of ditch management.     

The effects of cattle grazing on tall-herb fen vegetation and molluscs

The effects of light year-round cattle grazing on tall-herb fen vegetation and wetland molluscs were compared to the effects of non-intervention over a period of four years using grazing exclosures. The distribution of cattle within the area of fen was investigated by plotting the position of the herd at 3-4 day intervals throughout the year. Cattle distributed themselves randomly throughout the fen in spring, autumn and winter, but showed a more aggregated distribution in summer. Grazing reduced the biomass of Phragmites australis and increased stem densities of Glyceria maxima, resulting in a shift of dominance from Phragmites to Glyceria. Plant species-richness was also significantly higher in areas open to grazing.Grazing decreased total densities of molluscs and substantially reduced densities of the rare snail Vertigo moulinsiana. V. moulinsiana was particularly associated with areas of fen that had a high water table and high biomass of ungrazed Carex riparia. However, because of the patchy nature of the grazing, V. moulinsiana survived at reasonably high densities in patches of ungrazed vegetation within the grazing unit.     

雷州半岛红树林区软体动物多样性与生物量研究

2002年7～9月对雷州半岛8个主要红树林区软体动物进行了清查，记录有37科110种软体动物，且各红树林区的软体动物区系组成存在较高的地理分布上的差异(相似度均小于61．0％)。各红树林区的软体动物平均生物量为206Ind．／m^2或106g/m^2；树栖软体动物平均生物量为20Ind．／m^2或14．7g／m^2，树栖贝类优势种类有黑口滨螺等；地栖平均生物量为197Ind．／m^2或100．6g／m^2，以殊带拟蟹守螺等为优势种。生物量的大小主要与底质和林区群落特征有关，底质为淤泥土壤和高密度的群落生物量较低，泥沙质土壤和较低密度的群落的生物量较高，同一群落类型以林外缘带的软体动物的生物量最高。由于人为过渡采挖和环境污染严重，绝大部分软体动物种质资源趋于濒危状态，急需加强保护。