Annual quantitative distribution of meiofauna in relation to sediment environment in Qingdao Bay

The abundance and biomass of meiofauna as well as benthic environments factors were investigated in silt-sand(near to bank) and sand(close to the sea) in Qingdao Bay,China,based on monthly samplings from June 2006 to May 2007.The results showed that the contents of the chlorophyll a,phaeophytin and organic matter in the surface 0-2 cm sediment were higher in the silt sand than those in the sand.The annual average abundance of meiofauna in the silt sand((4853±1292) inds/10 cm2) was more than three times higher than that in the sand((1528±569) inds/10 cm2),and the biomass was about two times higher in the silt sand than in the sand((3186.9±1993.4) μg dwt/10 cm2 vs(1601.5±786.2) μg dwt/10 cm2).The meiofauna in the sand showed a bimodal abundance pattern,with higher values in early summer(June) and early winter(December) and lower values in early spring(March) and early autumn(September).The abundance of meiofauna in the silt-sand peaked in June and reduced to the lowest in November,but no clear pattern could be recognized.Within the 0-8 cm deep sediment,about 48% of the meiofaunal abundance was distributed in the 0-0.5 cm surface layer and over 86% in the 0-4 cm layer.Two contrasting patterns were observed in the vertical distribution of meiofauna in the two sediments: about 61% of total meiofauna occurred in the 0-0.5 cm surface in winter-spring and 42% in summer and autumn in the silt sand,while in the sand only 26% of total meiofauna was distributed in winter-spring and 66% in summer and autumn.Among the 13 meiofaunal groups sorted,nematodes were numerically predominant,accounting for about 95% of total abundance in the silt sand and 66% in the sand.Other main groups included Polychaeta(2%),crustacean nauplii(2%) and Copepoda(1%) in the silt sand and crustacean nauplii(13%),Gastrotricha(8%) and Copepoda(6%) in the sand.As concerns the biomass,nematodes contributed to 58% of total meiofaunal biomass in the silt sand,while in the sand nematodes(25%) were surpassed by Gastrotricha(28%).Pearson analyses suggested that meiofaunal abundance in the sand was positively correlated with the content of sediment organic matter(r=0.731;p0.01) and negatively correlated with the content of phaeophytin(r=-0.627;P0.05),while no correlation was observed between those in the silt sand.Cluster analyses indicated that the similarity was 87% in the benthic environments and 71% in the components of meiofaunal abundance between the silt-sand and sand sediments.Based on the BIOENV analysis,the combination of temperature,salinity,medium size and content of clay and silt accounted for the abundance differences in the sites and sampling months(r=0.614).Our study indicates that,in comparison with historic record,the environmental condition in the sand sediment has been greatly improved.However,the pollution situation in the silt-sand sediment is still serious,as indicated by the very high abundance of meiofauna,the extreme predominance of nematodes and the very high nematode/copepod(N/C) ratio.