||The aim of this study was to understand the composition of shrimp, crab and mantis shrimp assemblages and to investigate the relationship between their seasonal variation and environmental factors in the southern coastal waters off the Zhuoshui River. Furthermore, based on the growth parameters and seasonal variations of several dominant species, their estuarine utilization was hypothesized. The sampling was conducted at three stations on the southern coast of the Zhuoshui River mouth from March 2012 to September 2014. Environmental factors including seawater surface temperature, surface salinity, dissolved oxygen, chlorophyll a concentration, turbidity, nitrates, silicate and sulfite were collected simultaneously. The results revealed that seawater temperature, dissolved oxygen, chlorophyll a concentration, turbidity, transparency, nitrates, nitrite and sulfite varied monthly. Higher temperatures and chlorophyll a concentration were related to the wet season. In total, 61 species belonging to 15 families and 33 genera were collected, but the accumulative species number was not steady. The seven dominant species by abundance were Parapenaeopsis hardwickii（66.1%）, Portunus hastatoides（10.0%）, Metapenaeus joyneri（7.6%）, Parapenaeopsis cornuta（2.7%）, Penaeus indicus（1.9%）, Metapenaeus ensis（1.6%）, and Nematopalaemon tenuipes（1.4%）. Significant temporal variation of the assemblages was observed due to the different compositions of the dominant species. Among the seven, N. tenuipes was abundant between December and February, whereas the others were more abundant from June to August. P. hardwickii and P. hastatoides could be captured throughout the year, but with seasonal variation. The abundance of M. joyneri and N. tenuipes controlled the composition of dry and wet season groups, respectively. |
The grouping of estuarine crustaceans is related to seasonal variation of the hydrological characteristics. M. ensis and P. cornuta appear at high water flow and high temperature, whereas N. tenuipes prefers low temperature, high nutrients and high turbidity.
Temporal variation of the assemblages was related to the recruitment and habitat usage of the dominant species. In early summer and late autumn, P. hardwickii and P. hastatoides recruit in coastal waters and are abundant when the temperature is rising during the wet season. As the water temperature is higher than 16°C on the southern coast of the Zhuoshui River mouth, less mature M. joyneri were captured and a large number of sub-adults appeared from June to September, revealing a vital nursery ground for the juvenile M. joyneri.