| Salt mash is one of the most widely distributed wetlands in the estuarine and coastal area, but also one kind of the ecosystems which are disappearing at the highest speed. Macrobenthos, mainly invertebrates, inhabiting in the sedimentary environment of the salt marsh, are key links of trophic chains in saltmarsh ecosystems. And they play a relevant role in regulating the ecosystem structure and functions. The studies on the macroinvertebrate functional group emerging in last decades. In this approach, the macroinvertebrate communities are divided into different groups, and each group has the same or similar ecosystem characteristics. Through those methods, simplifying the analysis on the structure and function of the community is available. The division of the functional groups is more comprehensive for reaction to environmental changes with weakening the role of individuals. It is a more efficient way to reflect the characteristics of the habitat of the communities than conventional ways.In this study, the benthic macroinvertebrate and the sediment were surveyed in fixed sampling sites on the saline algae zone of ChongmingDongtan by seasonal frequency. And on this basis, the macrobenthic community was divided into feeding habit groups, feeding form groups and life style groups, after that their temporal-spatial distribution characteristics were analyzed. Furthermore, their relationships with sediment physicochemical factor are analyzed, and the main results are listed as follows:1.The composition and distribution characteristics of the benthic macroinvertebrate functional groups.1) Total 29 species were recorded during the surveys, which belong to 4 phyla,5 classes 16 orders,27 families. There were 4 bivalves,10 polychaetes,3 gastropods, 11 crustaceans and 1 anopla. The dominant species were Potamocorbula amurensis and the frequently recorded species were Corbicula fluminea and Grandifoxus cuspis. The communities were classified into diversiform functional groups according to their e ecological functions, which are the feeding habits, feeding forms and life styles. In this paper, the feeding habit groups has omnivores, herbivores, and carnivores, and each has 17,7 and 5 species respectively; the feeding form groups contains collectors, predators, filterers, scrapers and shredders, and each has 12,6,5,4 and 2 species respectively; and the life style groups including epifaunas, semi-infaunas and infaunas, each has 13 12 and 4 species respectively.2) The multiple classified functional groups showed various distribution characteristics. Viewed from the point of species number, highly significant difference (p≤0.01) was indicated by the species number of the life style groups among the seasons, while the species number of feeding habit groups and feeding form groups were not significantly different (p>0.05). And the species number of the feeding form groups was the only one that showed significant difference (p≤0.05)among the sections from the west to the east, and all of the groups were not significantly different (p>0.05) among the North-South sections. As for the density, the feeding habit, the feeding form and the life style groups were all highly significantly different (p≤0.01) among the different seasons and and also among the North-South sections, while they were not among the West-East sections (p>0.05). From the point of the biomass, the life style groups hadn’t shown any significant spatial-temporal difference (p>0.05), while both of the feeding habit and the feeding form groups were high significantly different (p≤0.01) among the different seasons.In addition, the functional groups of the same division mode also showed different temporal-spatial distribution characteristics. Such as the feeding habit groups, the density of the herbivores was highly significantly different (p≤0.01) among the sections from the north to the south, as well as the biomass of the herbivores among the sections from the west to the east. The species number of the carnivores was highly significantly different (p≤0.01) among the sections from the west to the east and also those from the north to the south.The density of the carnivores was highly different (p≤<0.01) among seasons. There was extremely significant difference (p≤0.01) among sections from the north to south of the species number of the omnivores, and both the density and the biomass of the omnivores were highly significantly different (p≤0.01) among thedifferent seasons. And among the different sections from the north to the south, the density of the omnivores showed significant difference (p≤0.05). To the feeding form groups, the density of the predators showed highly significantly different p≤0.01) among the different seasons, the distribution of scrapers mainly varied among the different seasons, while the distribution of filterers mainly varied among the sections from the north to the south. Both of the species number and the density of the shredders were highly different (p≤0.01) among the North-South sections, while the collectors were neither significantly different (p>0.05)among the different sections nor among the different seasons. To the life style groups, both of the species number and the density of the different groups were highly significantly different (p≤0.01) among the sections from the north to the south, while the biomass didn’t show t significantdifference (p>0.05) among the sections from the north to the south. Both of the density and the biomass of the semi-infauna were highly different (p≤0.01) among the seasons, while the species number of epifaunas was significantly different (p≤0.01) among the sections from the west to the east.2. The distribution characteristics of the sediment physicochemical factors.The temporal-spatial distribution characteristics of the sediment physicochemical factors varied with the different sediment types. The parameters of pore water mainly varyed with seasons and the sections from north to the south. As for sediment nutrients parameters, a highly significant difference (p≤0.01) was found not only among the different sections but also among the different seasons on the surface layer (0-2cm、0-5cm), while the nutrient parameters in deeper layer (5-10cm、10-15cm) showed no statistic difference (p>0.05). For the sediment grain size, the middle grain size of the sediment in the different depths varied with the seasons and the sections (p≤0.01), and the sediment sorting coefficient mainly varied with the sections from the north to the south.3. The relationships between the functional groups and the sediment physicochemical factors.1) The key impact factors affecting the distribution of functional groups mainly relyed on the habitat condition. The key factors for the different functional groups inhabiting in the similar habitatwere similar. In the saline algae zone of Chongming Dongtan, the parameters affecting the density of the feeding habit, the feeding form and also the life style groups all contained pore water temperature (Tw), salinity (Sal), sediment total carbon (TC), total nitrogen (TN), total organic carbon (TOC), middle grain size (Md), and sorting coefficient (Sc). Furthermore, the former three (Tw, Sal, TC) were also the factors that affectiong the biomass distribution of the various types of groups.2)The factors, including the pore water quality, the sediment nutrients and grain size, appeared to be uncorrelated with the species richness and the biomass of the different functional groups (P>0.05), while a close link with the density was indicated. (P≤0.05). When the benthic macroinvertebrates were classified into the different groups according to their ecological functions, a certain type of sediment factors which had close relate to them had been highlighted. Sediment nutrients (λa=0.114), sediment grain size (λa=0.112), and pore water factors (λa=0.080) were ranked by λa meaning for theimportance to the density of the feeding habit groups. They were in the same order sediment nutrients (λa=0.169), sediment grain size (λa=0.132) and pore water factors (λa=0.045) when it comes to the density of the feeding form groups. As for the density of the life style groups, sediment grain size appeared to be the most important (λa=0.205), followed by sediment nutrients ( λa=0.119) and pore water factors (λa=0.101).3) The relationships between the individual functional group and sediment factors varied among the groups within the same classification. From the perspective of the species number and biomass of the groups, most groups had significant correlationships (p≤0.05) only to a few of the sediment factors. But when it came to the density of the groups, there was at least one group under each classification showed significant correlationship (p≤0.05) with the most of the sediment factors. Such as the omnivores of the feeding habit groups, the shredders and filterers of the feeding form groups, the semi-infauna of the lifestyle groups.This study mainly focused on the relationships between the benthic macroinvertebrate functional groups and sediment physicochemical factors.The results have some reference value for various studies, such as the studies on the ecosystem function depression, degradation, restoration and so on. However, due to the the variation of the regional condition, even in the similar habitat of the salt marsh, the correlations between the functional groups and the sediment physicochemical factors might also be different. It is essential to identify such variations according to the research objects and environmental conditions.The systematic and comprehensive studies on the macroinvertebrate functional groups and their corresponding applications to indicate the environmental effects are one of the important trends for the future study. |
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