Studies On Large-scale Distribution Of Polychaeta In Taiwan Strait And Its Adjacent Waters

As an important component of macrobenthos, benthic polychaetes are species-richness and widely distributed in the ocean. Bioturbation induced by polychaetes may have great impacts on sediment reworking. Also, they play vital important role in matter cycle and energy flow of benthic ecosystem, and this is not only because they are often the numerically dominant macrobenthic taxon, but also because of the diversity of their feeding modes. Since polychaetes directly contact with water column and sediments of their environment, many species are used as bioindicators in evaluation of marine environmental quality, and now they are widely applied in seashore environmental monitoring.Several integrated marine investigations have been carried out in Taiwan Strait and its adjacent waters before, and a lot of in-situ data were obtaind. However, similar investigations are rare now, so it is important to make clear what situation macrobenthos especially polychaetes are now in, in order to improve understanding of changes of ecosystem. As natural diets of economic fish, prawn and crab, polychaete high-biomass zones may indicate locations of fishery. Moreover, studies on relationship between polychaete distribution and environmental variables will help to understand the inner mechanism of distribution. The ecological study in Taiwan Strait and its adjacent waters were conducted on 169 sampling stations in summer and winter of 2006, and large-scale structure of polychaete assemblage was analysed. The main results are as follows:1. Total 20118 polychaete specimens were analysed, identified as 289 species, belonged to 45 families and 161 genus, among which 156 species were identified to species level. We found one new-record family (Pisionidae) and 10 new-record species. Dominant species of the seas are Mediomastus californiensis, Aglaophamus dibranchis, Sigambra hanaokai, Prionospio malmgreni, Sternaspis scutata and Aglaophamus lobatus, showing the nature of subtropical and tropical fauna. Species-richness zones are distributed around Pingtan island, inshore waters of southern Fujian province and offshore waters of western Taiwan.2. Mean abundance, mean biomass, mean H' value and mean J' value of polychaete are 269 ind./m~2, 2.27 g/m~2, 3.363 and 0.857 in summer cruise, and they are 326 ind./m~2, 2.96g/m~2, 3.357 and 0.826 in winter cruise. In general, high-abundance and high-biomass zones are situated in inshore waters of Fujian province, while low-abundance and low-biomass zones in Taiwan Shoal and southern research seas. High-diversity zones are mainly located in central and northern investigated seas and inshore sea of Fujian province, and high-evenness zones account for most of the stations.3. Compared with published data, polychaete abundance was higher than before whereas biomass was lower. The result also showed composition of dominant species had changed, Terebellides stroemii and Eunice indica were replaced by Mediomastus californiensis and Aglaophamus dibranchis. Polychaete high-biomass zones closely correlated with upwellings, because sufficient food supply benefits inhabitation of polychaetes.4. Polychaetes are firstly divided into two major ecotypes according to sediment type, one in finer sediment and the other in coarser sediment, and the species composition of these two ecotypes are greatly different. Ensuring all station groups contain more than 10 sampling stations, polychaete assemblages can be divided into 4 station subgroups. They show significant difference not only in species composition, but also in abundance, biomass, species number and diversity value, and the farther the geographical distance among station groups, the greater different polychaete species composition and environmental variables.5. Previous biocoenosis-types identified with macrobenthic data of Taiwan Strait and its adjacent waters correspond to station groups of polychaetes.