Disease in Zoanthids: Dynamics in space and time

Numerous diseases in benthic marine organisms have been recognized over the last decade. Here, a new disease (pathogen unknown) is described and quantified in space and time for Palythoa caribaeorum (Cnidaria, Zoanthidea) populations on the São Paulo coast, Brazil (23° S). The degree of environmental stress (moderate vs. high), depth and temporal variation (seasons, years) on the frequency of the disease was assessed by monitoring plots at two sites: Ponta Recife (continent) and Praia Portinho (São Sebastião island), and at two depths per site (0.5-1.5 m and 2.5-4 m). The disease spread outward from within the colony in a circular pattern. A transverse section extending from normal to diseased tissue showed a progression from normal polyps to pale, swollen polyps, followed by remnant spicule-like structures, and finally fine black matter and bare substratum in the middle of the lesion. The disease occurred in one or more portions of the colony simultaneously. Disease frequency and total area infected increased significantly with colony size. Generally, the disease affected ≤ 5% of the total colony area, and occurred when gonad development was maximal. Therefore, 20.5% (n = 306), and 14.6% (n = 578) of the population was infected in two consecutive years, respectively. Disease exhibited higher rates during summer (tourist season) and fall, and decreased significantly in the winter with the presence of cool water. Factors associated with the increased instance of disease during the summer were higher temperatures, precipitation and sewage; the opposite was noted in the winter. Disease frequency varied significantly between years, seasons, sites and depths. Colonies exhibited higher disease frequency in Ponta Recife characterized by high levels of sedimentation, increased turbidity and low levels of incident light with respect to Praia Portinho. Colonies in shallow water exhibited greater frequency of disease compared to those in deeper water. Physiological stress, low energy input, energy expenditure and energy re-allocation may increase the susceptibility of P. caribaeorum colonies to disease. It is suggested that this disease may play an important role in the life history of P. caribaeorum because of its influence on partial mortality, colony area, population size structure, reproduction and ultimately fitness. This represents the first report of disease-related mortality in reef zoanthids of the Southwestern Atlantic.