Abstract:

In 2018, the coral community distribution and environmental parameters around Ximaozhou Island of Sanya were surveyed. We recorded 68 species of reef building corals and two species of Millepora spp. Based on the nMDS analysis of coral reef benthic substrata, we divided the sites of Ximaozhou Island into zone 1 (the south/east side) and zone 2 (the west side). The mean live coral coverage is 13.6% for the whole island, 4.2% in zone 1 and 27.7% in zone 2. The diversity of coral species in zone 2 is higher than that in zone 1. The reefs in zone 1 are in a significant degradation state, while the reefs in zone 2 are relatively healthy with single dominant coral species. Compared with the historical data, the mean live coral coverage at the east sites decreased from nearly 40% in 2011 to less than 4% in 2018, showing significant degradation, while the coral reefs at the west sites did not show significant change, with branching Acropora spp. shifting to massive Galaxea fasciculis. The mean values of turbidity, dissolved inorganic nitrogen (DIN) and δ¹⁵N of Turbinaria ornata in coral reef of Ximaozhou Island are 2.54 NTU, 9.63 mol·L^-1 and 5.09‰, respectively. Our correlation analysis shows that the environmental factors could not explain the spatial distribution of the coral community. Therefore, we speculate that the extreme disturbance event caused by human activities may be the main cause for the spatial distribution of coral community in Ximaozhou Island and the significant degradation of coral on the east side in recent years, such as the turbidity event caused by random dumping of sediments from the Sanya River into Sanya Bay. It is necessary to strengthen the control of sediment dumping and human activities in Sanya Bay, to reduce the impact of sedimentation and nutrient enrichment, and to promote a gradual recovery of coral reefs in Ximaozhou Island.

Key words: coral community, Ximaozhou Island, coral reefs, environmental parameters, distribution