Cluster‐analytic definition of species ecological groups for a submerged barrier reef in Barbados, West Indies

Cluster analytic techniques were employed to define significant ecological groups of benthic species sampled in 2237 0.5 m × 1 m quadrats on a submerged barrier reef located off the Barbados west coast. For measures of species cover, number of colonies, presence‐absence, and cover of dead skeletal material, Lance and Williams' flexible sorting procedure defined eight species groups. Only four of these groups could be interpreted with confidence. Resolution of species groups increased with increasing environmental severity and decreased with decreasing species abundance. Highly resolved groups under strong environmental limitation included an Agaricia lamarcki ‐sponge‐antipatharian association on deep outer slopes and a distinctive Acropora cervicornis‐Madracis mirabilis ‐rubble association of ridge‐top positions. The next two groups, in order of resolution, differentiated under strong competitive interaction. Associations dominated by Siderastrea siderea‐Montastrea cavernosa and Montastrea annularis‐Porites astreoides consisted of large colony‐forming species as part of a larger complex “mixed” coral association. The other four groups consisted of rare but widely‐occurring species. Probable reasons for the low resolution of these groups including severe disturbance, random colonization, niche specialization, and methodological idiosyncracies, were discussed. The efficacy of clustering procedures was discussed in relation to objectivity and efficiency of field recognition.