Predicting regeneration of physical damage on a reef-building coral by regeneration capacity and lesion shape

Abstract

We present a relationship that predicts regeneration of physical damage 011 reef-budding corals as a f ~~n c t i o n of regeneratlon capacity and lesion shape. The great abundance of lesions on colonles in the field and the characteristics of the regeneration process indicate that the abll~ty of corals to regenerate damage is limited Regeneration, the extension of new coral tissue over a damaged area, slows down exponentially. WC. hypothesized that regenel-atlon IS a funct~on of (1) a specles speclfic regeneratlon capac~ty and (2) the amount of tissue that directly borders a lesion. A corollary IS that there should be a maximum amount of tissue that can be recovered for a certain amount of border. Consequently, there is a maximum l e s ~o n size that can be completely regenerated by the surrounding tissue depending on the shape of the lesion. We studied the regeneration process in field experiments and made circular lesions of 4 different size classes (83, 183, 243 and 406 mm2) on colonies of the main reefbuilding coral of the Caribbean, Montastrea annularis. Lesion size decreased rapidly at the onset of the regeneration process but the rate of regeneration slowed to zero and the curve representing lesion size with time approached an asymptote. This asymptote represents the slze of the area which is not recovered by the regenerating tissue at the end of the regeneration process. The value of thls asymptote increased w ~t h increasing lesion area, ~ndicating limited regeneratlon capacity. Larger lesions regenerated more tlssue than smaller lesions, but this difference was absent when the regenerated surface area was standardized to initial lesion penmeter This indicates that the lesion perimeter is the primary factor determining the amount of area that will be regenerated. M. annularis could regenerate a maximum of 4.7 mm2 of new tissue per mm of lesion perimeter length. Circular lesions larger than 130 mm2 will not b e regenerated. The dependence of regeneratlon on lesion perimeter results in lesion shape being of major importance for the degree of regeneration of physical damage (e.g. long narrow lesions may be closed, while circular lesions of much smaller size may never b e closed). A relationship is presented that predicts percentage regeneration on the basis of lesion shape, with shape b e ~n g defined as the ratio of initial lesion surface area to initial perimeter length This function predicts regeneratlon of phys~cal damage in M. annulal-1s for any slze and shape of lesion