The three most common zoanthid species (Coelenterata:Zoantharia) on the intertidal reef flat at Galeta, Panama, show distinct zonation. Zoanthus sociatus occurs on the highest part of the intertidal platform while the two other species, Zoanthus solanderi and Palythoa
caribaeorum have upper limits in the lower surf zone. Of the three, only P. caribaeorum continues to the subtidal fore-reef. Transplant experiments using colonies still attached to their original substratum showed higher colony growth rates on the reef flat than on the fore-reef.
Predation was intense on both Zoanthus species transplanted to the subtidal but not on P. caribaeorum. Differential caging and float transplants were used to separate the effects of fish predation from that of benthic polychaetes (Hermodice carunculata). Field transplants
and laboratory prey preference experiments indicate that H. carunculata attacks the smaller Z. sociatus polyps before the larger Z. solanderi and that it ignores P. caribaeorum. Transplants also indicated that fish predation was important on the fore-reef and in
the sea grass beds where neither Zoanthus species is usually found. Both Zoanthus species appear to exist in refugia from predation, Z. sociatus in the high, often exposed, area of the reef flat and Z. solanderi in the surf zone. Desiccation tolerance differs
markedly among the zoanthid species and correlates with their observed upper limits and their reaction to extreme low tide sequences. Zoanthus sociatus proves the most tolerant and occurs highest on the reef flat. Z. solanderi and P. caribaeorum were much less tolerant,
able to survive only a few hours of exposure in the sun. The latter species are limited to lower elevations. All three species are susceptible to massive damage when exposed during abnormally low tide sequences. At any point in time, their distribution patterns reflect both continuously active
factors, including competition and predation, and historical events, such as the time of the last major disturbance.
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