Fish species composition and community pattern in the continental shelf of northwestern South China Sea

To understand fish species composition, community pattern, dominant species and seasonal variation in the continental shelf of northwestern South China Sea, four otter trawl surveys were conducted in January and August 2006, and April and November 2007, representing winter, summer, spring and autumn, respectively. Sixteen stations were assigned in each otter trawl survey along the coastlines from eastern Leizhou Peninsula to southeastern Hainan Island. Fish collection and data analysis followed the National Marine Survey Standards (GB/T12763.6--2007). Totally 262 fish species, from 102 families and 20 orders, were collected in the four seasonal surveys. The results revealed that the highest species diversity was in winter with 166 species recorded and the lowest was in spring with 135 species recorded; 161 and 155 species were recorded in summer and autumn, respectively. The Order Perciformes was the most important fish group in the continental shelf of northwestern South China Sea; the highest species diversity recorded was the Perciformes in all four seasons, and 40 out of 72 species recorded year-round belonged to the Perciformes. Species found in all four seasons contributed to 80.34% of total fish biomass. Ninety-one species found only in a single season contributed to 1.62% of total fish biomass. The spatial pattern of fish communities was analyzed using the hierarchical clustering and non-metric multidimensional scaling (NMDS), five fish groups were indentified. The Group I, recorded in all four seasons, was located in the coastal waters of western Guangdong Province and consisted of 3 or 4 stations. The scale and the distribution area of the Group I were stable among seasons. The Group II, recorded in spring, summer and autumn, was located in the coastal waters of southeastern Hainan Island and consisted of 6--9 stations. The scale and the distribution area of the Group II had seasonal variation. The Group III, recorded in spring, summer and autumn, was located in the deep waters of eastern Hainan Island and consisted of 4 stations. The scale and the distribution area of the Group III were stable. The Group IV as a transitional community, recorded in summer and autumn only, was located in the deep waters of eastern Hainan Island and consisted of 1--3 stations. The scale and the distribution area of the Group IV were small and changed largely with season. The Group V as a mixed community, recorded in winter only, was also located in the deep waters