Cyclical mucous sheet formation on poritid corals in the San Blas Islands, Panama

Mucous sheets are common on poritid corals as well as other reef coelenterates, but the frequency, cause and function of these sheets have rarely been investigated. Porites furcata Lamarck and Porites astreoides Lamarck colonies at three sites in the San Blas Islands, Panama, were monitored for the presence or absence of mucous sheets every 2 d between 11 May and 27 August 1983. Concurrent measurements of polyp expansion, particulate matter concentrations, salinity, water temperature and sedimentation rates were also made at each site. Mucous sheet formation was not correlated with any of the environmental parameters measured. Mucous sheet formation by both species had a lunar periodicity. P. furcata formed mucous sheets around the time of the full moon, while P. astreoides formed mucous sheets during the first quarter (around a week before full moon). Mucous sheet formation was correlated with polyp contraction behavior and may be a secondary effect of a lunar cycle in polyp activity.