Effects of extreme rainfall, typhoons and declaration of marine reserve status on corals beached at Cape d'Aguilar (1998 and 1999)

Abstract

In the years 1996 and 1997, the pattern of deposition of beached coral heads and pieces onto the shore of Telecom Bay within the Cape d'Aguilar Marine Reserve, Hong Kong suggested that typhoons were a significant natural perturbation. In August 1997, 808 pieces weighing 60,930 g were washed up following passage of Typhoon Victor. 1997 was also Hong Kong's wettest year on record and a survey of the living corals in the reserve in 1998 showed changes in a number of ecological parameters of species richness, composition and diversity but, most noticeably, that the formerly dominant Goniastrea aspera had been superseded by Platygyra sinensis. In 1998 and 1999, this was reflected in the changed proportions of these two beached corals. Dramatically lowered salinities in the bay during July and August 1997 may have effected this change in relative dominance. Following Typhoon Dan in October 1998, 342 pieces of corals weighing 75,600 g were collected. The 1996 and 1997 pattern seemed to be repeating itself. 1999 was a bad year for severe tropical storms and typhoons in Hong Kong, seven being reported upon. Yet, after each one only 12,490 g (Typhoon Leo), 3390 g (Typhoon Maggie), 3550 g (Severe Tropical Storm: no-name), 55 g (Typhoon Sam), 4500 g (Typhoon York and Typhoon Cam) and 3160 g (Typhoon Dan) were washed up. That is, the seven tropical depressions deposited about 27,640 g coral, approximately the same amount as only Typhoon Sally in 1996 (25,000 g) and Tropical Storm Penny and Typhoon Babs in 1998 (24,574 g) and less than half that of Typhoon Victor in 1997 (60,000 g). In July 1996, Cape d'Aguilar was declared a marine reserve, fishing banned in its 18 hectares of sea and ghost nets removed. The fishing ban seems to be halting the dislodgement of corals and they are thus not now being beached by typhoons.