Recovery dynamics of mechanically damaged scleractinian corals of the genus Porites under different light intensities

Abstract

Two types of injuries (breakage and hand-saw) were inflicted to the corals Porites lutea, P. cylindrica and P. rus. The injured colonies were maintained in outdoor aquaria for a period of 3 months under light intensities in the range from 0.8 to 90% of incident surface photosynthetic radiation (PAR0). The influence of bright (70-90% PAR0), moderate (20-30% PAR0), low (2-5% PAR0) and extremely low (0.8-1% PAR0) light on the dynamics, mechanisms and the recovery rates of the injured colonies, on the growth rates of coral fragments, on zooxanthellae population density in coral polyps and on chlorophyll concentration in zooxanthellae were studied. The regeneration of mechanical injuries inflicted on the corals had a similar character in all three species and the regeneration occurred in two stages. During the first stage (two-three weeks), damaged coral tissue recovered. Within the second stage (approximately two months) of the regeneration, living tissue expansion on the dead part of the damages and the formation of polyps by the newly formed tissue occurred. During the first stage, the regeneration rate of the injuries was more than two times higher (in average to 0.15mm per day for all Porites species) than during the second stage (in average to 0.06mm per day for all Porites species. Under low and extremely low light the density of zooxanthellae in the polyps decreased while chlorophyll concentration in zooxanthellae remained high. Light intensity had no significant effect on the regeneration rates. The growth rates of coral fragments were greatest in bright and moderate light, dropping sharply in low light, and the fragments did not grow under extremely low light.