Diversity And Community Structure Of Invertebrates In The Central Jiaozhou Bay

Jiaozhou Bay is an important area for fisheries in Shandong Peninsula. It is also the spawning ground and habitat for various kinds of economical marine species. Studies on ecology of invertebrates in Jiaozhou Bay has been carried out, most of which focused on benthic invertebrates communities. Researches on community structure of nekton invertebrates in Jiaozhou Bay have never been seen and the results of this paper will be a supplement for this field.Based on surveys of monthly bottom trawl in the central Jiaozhou Bay from September 2008 to August 2009, a study on invertebrate species composition, number of resources, community structure and diversity as well as the relations with environmental factors was conducted. Former data from 1986 to 1995 were also combined to discuss dynamic variations in invertebrate community in Jiaozhou Bay.There were 42 invertebrate species collected in all, isn which were 36 kinds of Crustacea and 6 kinds of Cephalopod. Crustacea were the major components of invertebrates in the central Jiaozhou Bay. All the invertebrate species were predominated by warm-temperate species of Yellow Sea. There was also a cold-water species called Japanese sand shrimp (Crangon affinis). According to their ecological habit, invertebrate species in Jiaozhou Bay could be divided into 2 ecological groups, i.e. resident species group and seasonal migratory species group. Compared to former data, there were few changes in resident species composition while there was a decrease in numbers of seasonal migratory species.Dominant species of invertebrates in the central Jiaozhou Bay varying among months were resident species and seasonal migratory ones such as mantis shrimp (Oratosquilla oratoria), white-hair rough shrimp (Trachypenaeus curvirostris), common European squid (Loligo sp.), smooth shell littoral shrimp (Parapenaeopsis tenella), whiparm octopus (Octopus variabilis), shortarm octopus(Octopus ocellatus), Japanese snapping shrimp (Alpheus japonicus), ridgetail white prawn (Exopalaemon carinicauda), Japanese sand shrimp, Lantern cuttlefish (Sepiola birostrata), Charybdis bimaculata and so on. Dominant species in autumn were mainly warm-temperate species and warm-water species like white-hair rough shrimp, smooth shell littoral shrimp and common European squid. With the decrease of bottom water temperature, dominant species in winter were mostly resident species, such as shortarm octopus, mantis-shrimp, Japanese snapping shrimp, and ridgetail white prawn. There was still Japanese sand shrimp, which was of cold-water. And with the increase of bottom water temperature, dominant species in spring were different from those in winter, which were Lantern cuttlefish, shortarm octopus, mantis shrimp, Japanese snapping shrimp, ridgetail white prawn, common European squid, whiparm octopus, smooth shell littoral shrimp and Charybdis bimaculata. In summer, dominant species included Charybdis bimaculata, white-hair rough shrimp, common European squid, mantis shrimp and whiparm octopus. Original economical dominant species of invertebrates in Jiaozhou Bay such as Japanese stone crab(Charybdis japonica), Common Chinese cuttlefish(Sepiella maindroni) and Chinese shrimp were replaced by small and low-economical species such as smooth shell littoral shrimp and Charybdis bimaculata comparing to former data.Relative biomass of invertebrates in the central Jiaozhou Bay was from 1.09kg/h to 23.54kg/h, and relative biological density was from 438ind/h～5290ind/h. There was a significantly positive correlation between relative abundance of invertebrates and bottom water temperatures. There was also an extremely distinctness in abundance between seasons, which was the highest in summer and the lowest in winter. In general, relative abundance of Cephalopod was much less than those of Crustacea, which were the major components of invertebrate resources in the central Jiaozhou Bay. Compared to the data from 1980s to 1990s, there was a marked decrease of invertebrate resources in Jiaozhou Bay. The percentages of different ecological groups also changed.Diversity of invertebrate community in the central Jiaozhou Bay was analyzed with univariate and distributional/graphical techniques. The results showed that there was no significant distinctness of diversity indices between seasons. There were also no correlations between diversity indices and environmental factors. Margalef species richness index R fluctuated between 1.648 and 2.529. The ranges of Shannon-Wiener diversity index H' and Pielou evenness index J' were 1.325～2.500 and 0.422～0.693 respectively. The variations of both indices basically followed the same tendency. The community structure of invertebrates in the central Jiaozhou Bay was relatively simple with low diversity which might be caused by low numbers of species, relative higher value of dominant species and the unique ecological geographical trait of Jiaozhou Bay.The analysis of multivariate methods showed that four month groups were identified for invertebrate community in the central Jiaozhou Bay. There were no distinct differences between each two groups while there was significant distinctness in all of the groups. The typifying species in each month groups were also the discriminating species in different month groups, most of which were the dominant species in each month groups as well. For example, mantis shrimp, white-hair rough shrimp, shortarm octopus, whiparm octopus and common European squid. The variations of relative biomass and relative biological density led to the discrimination between different month groups. Analysis combined with environmental factors affecting invertebrate community in the central Jiaozhou Bay indicated that bottom water temperature was the most important environmental factor in a single factor; the combination of bottom water temperature and salinity affected invertebrate community most in two factors; and the combination of bottom water temperature, salinity and depth was also an great influence to the invertebrate community in the central Jiaozhou Bay. Therefore, bottom water temperature was the main environmental factor to explain the variations of community structure of invertebrates in the central Jiaozhou Bay.