CORAL COLONY TISSUE-DAMAGE IN 6 SPECIES OF REEF-BUILDING CORALS - PARTIAL MORTALITY IN RELATION WITH DEPTH AND SURFACE-AREA

Partial mortality and its relation with colony size was assessed in co lonies of 6 species of reef-building corals (Scleractinia) at three si tes in 2 depth zones, reef terrace (7 m) and fore-reef slope (18 m), o n the fringing reefs of Curacao, Netherlands Antilles. Partial mortali ty is manifest on coral colonies as tissue lesions which have not been closed by the surrounding tissue. Two types of lesions were distingui shed: (1) Type I lesions, completely enclosed by living tissue, and (2 ) Type II lesions, not completely surrounded by tissue and open to the edge of the colony. These lesion types differed in occurrence and les ion size-frequency distributions, as well as in relation to variation in colony surface area and morphology. The percentage of undamaged col onies decreased with increasing colony size and lesion number increase d logarithmically with colony surface area. Larger colonies have littl e chance to escape partial mortality. The abundance of Type I lesions was significantly less on the reef slope, while the number of Type II lesions was greater. This is probably caused by a relative increase of the colony circumference because colony height is reduced on the reef slope. Median lesion sizes ranged from 0.5 to 3 cm(2) for Type I lesi ons and from 2 to 60 cm(2) for Type II lesions. Type II lesions covere d a much larger colony area than Type I lesions, suggesting that botto m-associated causes are relatively important with respect to partial m ortality. Species and colonies with large circumference relative to to tal colony surface area, such as plate-like and small colonies, were p articularly susceptible to partial mortality by Type II lesions. Whole -colony mortality rate of small juvenile corals was very high, but dro pped abruptly with increasing size, probably at the time that growth d irection changes from horizontal to vertical. This 'escape in height' makes corals less susceptible to partial mortality and represents an i mportant life history characteristic. There were important differences between the species. These are explained, after correcting for variat ion in colony size (surface area), by differences in colony morphology and lesion regeneration potential.