Meiofauna, a fundamental component of terrestrial and marine benthic ecosystems, form an integral element of food webs and play a critical role in nutrient recycling. To clarify the composition and ecological roles of meiobenthic communities within sediments of the Pearl River Estuary, Southern China, meiofauna composition, abundance, biomass and distribution were reported together with abiotic parameters (temperature and salinity of water, organic matter content organic and particle size of sediment) based on samples conducted at 16 stations (from 22.10° N to 22.80°N, 113.50° E to 114.00° E) in summer, 2010.
A total of 16 meiofaunal groups were identified in the whole sampling study. Free living marine nematodes were the most dominant group, with an abundance of (115±115) ind./10cm², accounting for 62.61% of the total meiofauna, followed by Bivalvia larvae (22.62%), crustacean nauplii (5.02%), and harpacticoid copepods (3.28%). The remaining groups accounted for less than 2% of total meiofauna, and included Polychaeta, Nemerteana, Echiurida, Ostracoda, Kinorhyncha, Oligochaeta, Turbellaria, Tanaidacea, Cnidaria, Acarina, Tardigrada and unidentified taxa. The average abundance, biomass and production of the meiobenthos was (183±174) ind./10cm², (345±334)μg dwt/10cm² and (3104±3008)μg dwt/10cm² respectively. Based on the meiobenthic biomass, the main dominant groups were bivalves (50.57% of total meiobenthos biomass), followed by nematodes (13.33% of total) and polychaetes (12.47% of total). Most meiobenthos (81.15%) were found distributed in the 0-5 cm layer of sediment. Vertical distribution was different for the dominant groups of the meiobenthos; bivalves and nematodes were in the 0-5 cm layer of sediment, most copepods were in the 0-2 cm layer, and polychaetes were in the 2-5 cm layer. Analysis of abiotic parameters showed that the average organic matter content of the sediment was 6.90%, which showed an increase from the west to the east of the estuary, and from the upper reaches to the lower. The dominant sediment type was poor sorted silt-clay, representing 84.39%-97.29% of total sediment and with median diameter (MDФ) from 6.56-7.18. This sediment type was found throughout most areas of the estuary. In the top 8 cm of sediment, average Chl-a concentration was 0.80 μg/g and the average organic matter was 6.90%.
The correlation analysis between meiobenthos and abiotic parameters indicated that the abundance of meiobenthos correlated positively with salinity, and negatively with temperature near the bottom, silt-clay content, median diameter (MDФ) and organic matter of sediment. The abundance of polychaetes and nematodes was also found to correlate negatively with bottom water temperature and positively with water salinity. The results of hierarchical clustering and multidimensional scaling (MDS) analysis of the sampling showed that all sites could be divided into three groups at the similarity level of 50%. The structure and diversity of the sampling sites were expressed using the Shannon-Wiener index, the Margalef index and the dominance index. Values of the Shannon-Wiener index ranged from 0.667-1.653, while the dominance index ranged 0.314-0.784. The mean nematode/copepod-ratio (N/C-ratio) showed an increasing trend from upper to lower reaches and from west to east of the estuary, which could correspond to the organic pollution of the Pearl River Estuary.