A Preliminary Study of Two Representative Seagrass Communities in Palau, Western Caroline Islands (Micronesia)

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Two distinctly different but representative seagrass communities were studied in the vicinity of Koror, Palau, Western Caroline Islands from May 21 to June 25 1978. The first community, a 30 m wide band adjacent to a beach, consisted primarily of Halodule uninervis (Forsk.) Aschers. and Cymodocea rotundata Ehrenb. and Hempr. ex Aschers. near the shore (Zone 1), then Thalassia hemprichii (Ehrenb.) Aschers. and Syringodium isoetifolium (Aschers.) Dandy (Zone 2) with T. hemprichii, C. rotundata and Halophila ovalis (R. Br.) Hook.f. at the seaward margin (Zone 3). The second site was an extensive tidal flat dominated by Enhalus acoroides (L.f.) Royle and T. hemprichii (Zone A). On the deeper seaward slope of this flat (Zone B), T. hemprichii disappeared while C. serrulata (R.Br.) Aschers. and Magnus appeared as depth increased. Enhalus density remained about the same in Zones A and B although the blades were larger (averaging 76 cm long and 2.1 cm wide) in Zone B than in Zone A (averaging 45 cm long and 1.5 cm wide). Blade elongation rates ranged from 1.2 to 3.0 cm week-1 for T. hemprichii with high variance and approximately 7.0 cm week-1 for Enhalus. Enhalus had a maximum blade elongation rate of over 2 cm day-1. All the broad-bladed seagrasses were grazed by fishes, presumably scarids and siganids, but grazers did not consume a significant amount. Fish grazing was almost entirely concentrated at the heavily epiphytized blade tips especially those of Enhalus. Infauna samples at both sites were dominated by polychaetes and bivalves and the total number of individuals increased as the seagrass biomass increased. Epifaunal macroinvertebrates (especially sponges, scleractinians, prosobranchs and ascidians) were particularly abundant in shallow Enhalus beds and thick subtidal Thalassia beds. The common macroalgae present at the two sites differed considerably except for the almost ubiquitous Amphiroa fragilissima (L.) Lamour.

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Aquatic Botany, v. 12, p. 229-244