Demographic Monitoring of juvenile Acropora spp. in the Florida Keys 2002

Caribbean acroporid species have undergone extreme declines in abundance since the 1980s. Population-level recovery will depend on re-colonization by juveniles (fragments or sexual recruits), which are particularly vulnerable to threats such as predation and disease. Demographic monitoring of juvenile Acropora cervicornis and A. palmata colonies was undertaken in the Florida Keys (USA) to determine the fate of various initial colony conditions as expressed by growth and survivorship over an 18 month study. Both healthy colonies and those with signs of recent predation or disease were selected at several sites, measured, photographed and reassessed periodically between summer 2002 and winter 2003-04. Most A. palmata colonies (72%) that were initially healthy were still healthy at the study's conclusion. Snail (Coralliophila abbreviata) predation resulted in partial mortality which decreased growth for A. palmata. Snail-infested colonies tended to retain snails for several months to a year. White-band disease affected several colonies throughout the survey but did not result in complete mortality of any tagged colonies. Only half of the initially healthy A. cervicornis colonies remained healthy, while 38% lost substantial tissue or died of a rapidly progressing disease of unknown etiology. Predation by the fireworm Hermodice carunculata was extremely common. Although it was associated with relatively little live tissue loss, it is postulated to have profound effects on growth since it feeds selectively on the growing tips. Regardless of initial condition, A. cervicornis lost substantial tissue more often than A. palmata suggesting that A. cervicornis may be even more imperiled than its congener.