枯季长江口南汇东滩潮间带盐沼湿地冲淤变化对大型底栖动物功能群的影响

Effects of sediment erosion and deposition variation on the benthic macroinvertebrate functional groups in an intertidal salt marsh of Nanhui Dongtan during the dry season,Changjiang River Estuary

盐沼湿地的冲淤变化是影响大型底栖动物功能群组成及其分布特征的一个重要因素。本文选择长江口南汇东滩作为研究区域,设置固定样地,分别于2015年11月和2016年2月,进行了大型底栖动物和沉积物理化因子的季节性取样分析,并在期间内每月进行滩面冲淤变化的观测,分析了枯季长江口南汇东滩潮间带盐沼湿地冲淤变化对大型底栖动物功能群的影响及作用机理。调研期间共采集到大型底栖动物37种,从功能群组成来看,以杂食者居多,共25种;植食者次之,共7种;肉食者最少,仅为5种。3种食性功能群的物种数、密度和生物量的时空变化特征有所不同。调研期间,3个功能群物种数都略有下降;植食者密度显著增加(P<0.01),而肉食者、杂食者密度变化不显著(P>0.05);3个功能群的生物量变化均不显著(P>0.05)。植食者密度和生物量在样地间都存在极显著差异(P<0.01);肉食者和杂食者仅密度在2016年2月的调研中存在样地间的显著差异(P<0.05)。不同样地月际冲淤变化特征有所不同,但总体均呈淤涨态势。多数环境因子存在显著的空间差异(P<0.05),仅不同深度的沉积物中值粒径在样地间无显著差异(P>0.05)。滩面冲淤变化对沉积物理化指标的变化具有主导作用。通过非线性回归分析筛选出的与各功能群物种数、密度、生物量变化具有显著相关性(P<0.05)的环境因子组合存在差异。其中,对植食者密度、生物量的变化和肉食者物种数的变化有显著影响的环境因子组合中都包含绝对冲淤变化量。滩面冲淤变化除对大型底栖动物产生直接影响外,还会通过改变沉积物理化因子特征,间接对大型底栖动物产生影响。对于3种食性功能群来说,产生影响作用的主要生境因子存在明显差异。虽然各食性功能群的物种数均有下降,但相对另外两种功能群而言,沉积物中的营养环境还是更利于杂食者的生存,因此杂食者在竞争过程中更具优势。未来相关研究需要在多因子系统监测的基础上,结合洪季的观测结果,进行综合分析。

The variation of sediment erosion and deposition in salt marsh is one of the important factors that affect the composition and distribution of the benthic macroinvertebrate functional groups.During dry season the Nanhui Dongtan in the Changjiang River Estuary was selected as the study area,with a fixed sample sites.On November2015 and February 2016,respectively,benthic macroinvertebrates,sediment physical-chemical factors were surveyed seasonally and erosion-deposition characteristics were observed monthly during the period.The effects of sediment erosion and deposition variation on the functional groups and corresponding mechanisms were analyzed based on these.A total of 37 species of the benthic macroinvertebrates were recorded during the surveys.Among them,25 species were omnivores,7 species were herbivores and only 5 species happened to be carnivores.These three different feeding habit functional groups appeared to have different spatial-temporal variation characteristics in number of species,density and biomass.Between the seasonal surveys,the number of species of the three different functional groups were all slightly decreased,and the density of the herbivore was significantly increased（P〈0.01）,while the density of the carnivore and omnivore appeared to have no significant changes（P〉0.05）.The biomass of the three functional groups did not change significantly（P〉0.05）.Both the density and biomass of the herbivore showed extremely significant differences among the sampling sites（P〈0.01）,while the carnivore and omnivore only showed such kind of significant difference in density in February 2016（P〈0.05）.Monthly variation characteristics of sediment erosion and deposition appeared to be different in the different sites,but all sites tended to be silted.Most of the environmental factors had significant spatial difference（P〈0.05）,except the median grain size of the sediments in the different depths.Sediment erosion and deposition appeared to lead the variations of the physical-chemical factors of the sediments.It was varied that the combinations of selected environmental factors which were significantly correlated with the number of species,density and biomass varied with groups.The absolute amount of sediment erosion and deposition appeared in the combinations of environmental factors which were significantly correlated with the variations of the density and biomass of the herbivores and number of species of the carnivores.In addition to the direct effect on the macrobenthos,the variation of the sediment erosion and deposition will also indirectly affect on the macrozoobenthos by changing the characteristics of sedimentary physicochemical factors.The main factors which had effects on the different feeding-habit functional groups appeared to be different.Although the species number of feeding habit functional groups decreased,the nutrient environment in sediment was more favorable to the survival of omnivores than the other two functional groups.Therefore,omnivores have an advantage in the competitive process.Further comprehensive studies should be carried out based on the systematic monitoring and the combination with the observation results of flood season.