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Effects of tropical storm Bret on Curaçao reefs

1995; Rosenstiel School of Marine and Atmospheric Science; Volume: 56; Issue: 2 Linguagem: Inglês

1553-6955

M. L. J. Van Veghel, Paul Hoetjes,

Crustacean biology and ecology

It is obvious that hurricanes can have a destructive effect on reefs situated on the leeward sites of islands (Glynn et al., 1964). However, also minor storms passing at relatively great distance can cause severe damage. Here we report on damage caused by tropical storm Bret, passing south of the island of Cura9ao at a distance of 110-145 km in August 1993. Curacao is situated off the coast of Venezuela and outside the hurricane belt (Rogers, 1993). The closest approach to Curacao of Bret was on 8 August 1993, from 06.0008.00. Maximum wind velocity measured at the Curacao Meteorological Service was about 42 kn, mean value: 25—30 kn. The estimated wave height near the location Seaquarium was approximately 1.5 m above normal. The storm was not accompanied by heavy precipitation. Bret was the 21st tropical cyclone passing Curacao within 100 nm since 1900, the former cyclone was Joan in 1988. Damage on marine life was surveyed 2 weeks after the storm at five localities along the leeward coast of the island (Fig. 1; for detailed information on the study sites see Van Duyl, 1985). In selection of the sites we were guided by Van Duyl's (1985) reef atlas. Severe damage was recorded for the scleractinian corals Acropora palmata (Lamarck) and Millepora complanata (Lamarck). Dendrogyra cylindrus (Ehrenberg) was incidentally damaged in shallow water, 20 cm) of haphazardly chosen colonies. In A. palmata 43% to 89% of colonies were damaged in four localities, no damage was observed at Playa Kalki. In these colonies 25% to 50% of the branches were broken off. Damage on A. palmata was found at 4 localities up to depths over 8 m (Table 1). There was a clear decrease in living coral of A. palmata colonies at these sites. Most fragmented branches that were detached were bleached and likely to die. This is in contrast to Bak and Criens (1981), who found virtually no mortality after experimentally breaking up colonies. Postbreakage mortality after the storm is probably a result of such storm associated factors as continued high wave energy, scouring (Knowlton et al., 1981) and sedimentation. An abrupt decrease of water temperature from 27°C to 23.6°C registered about 40 h after the storm can be considered as one of the major delayed effects (Fig. 2). This sudden temperature change is larger than the average annual fluctuation and was registered on a Ryan Instruments thermograph situated at a depth of 30 m near CAR-MABI Buoy 1 (see Van Veghel, 1994). Temperature was normal 3 d after the decrease. The storm must have effected the process of sexual reproduction since the A. palmata colonies were carrying gonads (Van Veghel, pers. obs.). This simply was a consequence of the die off of living tissue or regeneration processes (Van Veghel and Bak, 1993). Millepora complanata was surveyed from 2 to 6 m at 1-m intervals. Colonies