Abundance Distribution of Holothuroids (Echinodermata: Holothuroidea) on a Windward and Leeward Fringing Coral Reef, Guam, Mariana Islands
Abstract:We used line transects to determine the abundance distribution of holothuroids on a windward (Pago) and leeward (Tumon) reef on Guam. In a total sample space of 11,134 m2 between depths of 0 and 23 m, we recorded 20,283 holothuroids comprising 19 species. Another five species were recorded as single individuals off the transects. Holothuria atra was the most abundant species recorded and comprised 92% of the holothuroids counted at both sites. The two next most abundant species were considerably less common: Actinopyga echinites and H. leucospilota were 3% and 2% of the enumerated fauna, respectively. Each of the remaining 20 species were 1% or less of the total fauna. Species richness and a species' relative abundance between sites appeared related to overall reef exposure. Species richness was slightly less for Pago (20) than for Tumon (22). Pago had much lower densities of the largest, epibenthic holothuroids common at Tumon, Bohadschia argus, Stichopus chloronotus, Thelenota ananas and H. nobilis. Conversely, between-site abundances of cryptic holothuroids were similar. These observations suggested that storm-generated waves, which often devastate the windward reef at Pago, may strongly influence the holothuroid community there. Within-site species richness was associated with physiographic zones. The middle reef flats had the greatest number of species (20) of any reef zone, while reef slopes supported ten species. The fewest number of species, four, occurred along the reef margin, and only two species, Actinopyga mauritiana and H. cinerascens, were found there in abundance. Species abundances at smaller scales were less predictable. Pairwise product-moment correlation analyses of species abundances at Tumon showed that most distributions were independent of one another when enumerated within 10-m2 and 2-m2 quadrats. Less often, there were weak but significant positive correlations. Weak but significant inverse correlations existed between Holothuria atra and three holothuroids found mainly on the reef front or reef slope, A. mauritiana. H. nobilis and S. chloronotus. Each microhabitat supported more than one species, and species were often found in more than one microhabitat: Rubble-and-sand bottoms and areas under rocks each supported 11 species, seven taxa were seen on sand, while three species were found in sand. Macroalgae, turfaceous-algae-covered pavement, the surface of live coral and bare pavement had five, three, two and two species, respectively.
Document Type: Research Article
Publication date: 1993-03-01
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