A non-destructive method for monitoring coral growth affected by anthropogenic and natural long term changes

Natural and man-induced changes lead to severe degradation in the viability of aquatic ecosystems. The excessive demands under which coral reef communities are being placed may soon result in the failure and dysfunction of these ecosystems. Such observations have led researchers to draw attention to the urgent need for establishing long-term monitoring programs, It has becn suggested that coral growth characteristics can serve as biosensors for environmental variables, We therefore propose an in situ method for recording the growth of transplanted and intact coral colonies. The technique permits a facile, highly reproducible and non-destructive long-term monitoring operation. In the last decades we witnessed a widespread concern over the apparent decline in the abundance and diversity of coral reef ecosystems. (Hudson, 1981; Hudson et al., 1982; Tomascik and Sander, 1985; Grigg and Dollar, 1990; Duarte et aL, 1992) These were attributed to some direct destruction by various human activities, as well as to global climate-change related phenomena. However the exact causes and mechanisms of the decline are not yet fully understood (Duarte et aL, 1992). Recent rapid increase in the utilization of coastal marine resources is a worldwide phenomenon. It has become apparent that as a result these ecosystems cannot always remain viable under the excessive demand (Dahi, 1992; Oliver and Schneider, 19921). Coral reefs can be damaged by a large number of natural and anthropogenic factors. Reef building coral have undergone mass mortalities along the pacific coast of Panama following the 1982/1983 El Nino event (Glynn, 1983, 1984, 1989). Bleaching events of shallow water corals were observed on the Great Barrier Reef which were correlated with the time of maximum water temperature and greater than average hours of sunshine (Gates, 1990; Lesser et al., 1990). Serious mechanical damage may be caused in coastal and off-shore waters involving development, tourism and fishing. Prolonged eutrophication derived from sewage runoff and dredging were associated with dense growths of the "green bubble algae" and mass mortality of the stony corals on the island of Oahu, Hawaii (Maragos et aL, 1985). Tomascik and Sander (1985) reported on reduced growth rates of corals along a eutrophication gradient in Discovery Bay, Jamaica. Increased sedimentation is likely to be one of the most common and severe anthropogenic impacts on coral reefs. The effects of sediment stress have been reviewed by Dodge and Vaisnys (1977) and recently by Grigg and Dollar (1990) and Rogers (1990). Deleterious damages caused by sedimentation, resulting in the blanketing of the coral colonies by suspended particles. Indirect impacts resulting from sedimentation often leads to eutrophication and alteration of the surrounding physical environment, which in some cases induce physiological stress effects (Grigg and Dollar, 1990). Such effects may lead to ecosystem dysfunction and internal dynamic breakdown. I Oliver. J. and R. Schneider. 1992. Monitoring the impact of tourist developments in the Great Barrier Reef Marine Park: some case studies. Proc. 7th In! Coral Reef Symp. Abs.