Degradation trend of coral reefs in the coastal waters of Vietnam

Abstract

Monitoring of coral reefs in Vietnam have been conducted at 42 permanent sites in seven key areas in the coastal waters of Vietnam, including Cu Lao Cham, Van Phong Bay, Nha Trang Bay, Ninh Hai – Ninh Thuan, Ca Na Bay, Con Dao and Phu Quoc, using SCUBA diving. The numbers of reefs in excellent and good conditions decreased from 7.4% and 33.3% in the period of 1994-1997 to 2.9% and 11.6% in the period of 2004-2007 respectively. The number of coral reefs in bad and very bad conditions increased from 14.8% (1994-1997) to 50.0%(2004-2007). The percentage of coral reefs in fair condition remained relatively stable, averaging 44.5% (1994-1997) to 40.6% (2004-2007). The quality of most coral reefs has been significantly decreasing between 1994-2007, with annual degradation rate averaging 1.14% for live corals, 0.93% for hard corals and 0.27% for soft corals. Total density of fish significantly increased over time, with mainly increasing density of small fish at size class of 1-10 cm. Density of large fish (＞20 cm), mainly target and predatory fish decreased over time. The target indicators of macro-invertebrates are extremely rare with the exception of sea urchins and crown of thorn starfish. Density of top shells, edible sea cucumbers and crown of thorn starfish slightly increased while giant clams and sea urchins significantly decreased over time. Ratio of reefs with active outbreak of crown of thorn starfish in the central of Vietnam increased from 0% in 1998 to 45.5% in 2002 and 35.7% in 2007. This indicates that coral reefs in the coastal waters of Vietnam are not in good condition and have been degrading over time.