The Ecological Study On Macrobenthos In The Rocky Zone Of Islands In Zhejiang

The sampling investigation on macrobenthos was conducted among the intertidal and subtidal zones in the rocky area of Zhejiang islands from June to July in 2007. Four surveyed marine areas has been set running from north to south, namely, Shengsi, Zhoushan, Dachen, Nanji. Each marine area has several island sections for sampling according to the actual environment. Based on the sampling data, makes full description and discussion about the macrobenthos in the rocky area of Zhejiang islands on their biological composition, species diversity, and floral composition and also makes analysis involving the subtidal macrobenthos on their abundance and dominant species. On this basis, the partition of community structure is made by the results of Bray-Curtis similarity dendrograms and MDS.The following is the main findings of this thesis:1,174 species from intertidal zone and 183 ones from subtidal zone have been gathered in this investigation. In term of the biological composition, Mollusk, Rhodophyta and Crustaceans are the main species in both the intertidal and subtidal zones with only small amount of other species. The species number of benthic algae and Annelida in intertidal zone is more than that in subtidal zone, while the species number of Coelenterate and Echinoderm is just the other way around. As for the space distribution of the species in different marine areas, the species number in Shengsi and Nanji is more than that in Zhoushan and Dachen.2, Nanji marine area is the tiptop regarding both the species richness and diversity index in subtidal zone. On the aspect of diversity index, all the sections in both intertidal and subtidal zones turn out low in the average taxonomic distinctness△+ while high in the variations in taxonomic distinctness∧+. The reason is that the species of each section mainly belong to some certain category units such as Rhodophyta and Mollusc while other categories have very small species numbers and dispersed category composition. It indicates that the biotic community of the local macrobenthos may be suffering a certain kind of disturbance with some categories existing in adverse environmental condition or being over exploited.3, Shengsi and Nanji marine areas surpass Zhoushan and Dachen marine areas on the abundance value of macrobenthos in subtidal zone, which is in accordance with the space distribution of species composition. As for the dominant species composition based mainly on Mollusc, some eurythermic Molluscs, such as Modiolus comptus, Tais luteostoma, Septifer virgatus, Monodonta labio, Mitrella bella, play a leading role in the community composition of macrobenthos in subtidal zone. With the reducing of latitude, the number of subtropical even tropical species increases gradually and these species begin to become the dominant species.4, The community structure is much different between intertidal zone and subtidal zone, which has something to do with the enormous differences on the environmental elements between these two zones. Moreover, there are also significant differences between the northern Zhejiang and southern Zhejiang on the community structure. According to the results of Bray-Curtis similarity dendrograms and MDS, intertidal zone and subtidal zone can be further divided into five community groups: community group of subtidal Dachen section, community group of subtidal Shengshan island—Gouqi island—Dongji island—Yangqi island, Nanji archipelago, community group of intertidal Shengshan island—Gouqi island—Julangbei, community group of intertidal Sijiao—Zhujiajian—Fengweicun. The divergence between each community group has some connection with the combined influence of fresh water, latitude and ocean current.5, The whole macrobenthos flora in the rocky reef area of Zhejiang islands has the characteristics of the subtropical flora, with the dispersed species and subtropicsⅡspecies play a dominant role. Latitude and ocean current elements have a major part in the flora composition. There are more temperate species in Shengsi marine area of northern Zhejiang due to its high latitude. However, some subtropical and tropical species can also be found in a relatively large number for the influence from the warm current of open seas. As depressing of latitude, more subtropical and tropical species be found, and the subtropical flora begin to transit towards tropical flora. Some tropical species such as Coscinasterias acutispina turn into dominant species in Nanji marine area.