Naturally occurring interactions in three Montastrea annularis morphotypes, viz. Bumpy, Massive and Columnar (Van Veghel and Bak, 1993), were surveyed at six different depths on three localities along the leeward reefs of Curaçao, Netherlands Antilles. In addition we did
experiments to study the competitive abilities of the three morphotypes using four scleractinian opponents. Intraspecific interaction in M. annularis played a minor role in competition on the reef, compared to interspecific interactions (5 versus 95%). In naturally occurring interactions
with other scleractinians two out of 18 encountered species deviated from Lang's (1973) hierarchy, in interactions with the Bumpy and Massive morphotype, and four species showed deviations in interactions with the Columnar morphotype. Bumpy and Massive morphotypes were more frequently involved
in interactions on the reef than the Columnar morphotype. The Bumpy morphotype was the most dominant competitor of the three morphotypes. The hierarchical ranking observed in natural encounters can be expressed as the ratio dominance:subordinance of M. annularis morphotypes; Bumpy (3:1)
> Massive (2:1) > Columnar (1:2). This resembles the intraspecific interaction pattern (Van Veghel and Bak, 1993). Our experiments, designed to measure competitive ability as size of lesions resulting from mesenterial combat, produced a similar hierarchical pattern. Quantity and/or length
of mesenterial filaments are suggested to be responsible for differences in competitive ability between the M. annularis morphotypes.
The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.