Experimental fragmentation reduces sexual reproductive output by the reef-building coral Pocillopora damicornis

Natural and anthropogenic disturbances may fragment stony reef corals, but few quantitative data exist on the impacts of skeletal fragmentation on sex ual reproduction in corals. We experimentally fragmented colonies of the br anching coral Pocillopora damicornis and determined the number and size of planula larvae released during one lunar reproductive cycle. Partially frag mented colonies significantly delayed both the onset and peak period of pla nula release compared with intact control colonies. Most fragments removed from the corals died within 11-18 days, and released few planulae. The tota l number of planulae released per coral colony varied exponentially with re maining tissue volume, and was significantly lower in damaged versus undama ged colonies. However, the number of planulae produced per unit tissue volu me, and planula size, did not vary with damage treatment. We conclude that even partial fragmentation of P. damicornis colonies (<25% of tissue remove d) decreases their larval output by reducing reproductive tissue volume. Re peated breakage of corals, such as caused by intensive diving tourism or fr equent storms, may lead to substantially reduced sexual reproduction. There fore, reef management should limit human activities that fracture stony cor als and lead to decreases in colony size and reproductive output.