Ecological Studies on the Sea Urchin, Lytechinus variegatus, and the Algal-Seagrass Communities of the Miskito Cays, Nicaragua

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Benthic vegetation patterns and sea urchin abundances, feeding and reproductive activities are described along a gradient from shallow lagoons to depths of 8 m. Shallow waters (1 m) are characterized by dense beds of Thalassia testudinum Banks ex König, a depauperate algal flora and moderate urchin densities. Siphonous green algae and seagrasses typify intermediate depths (2-4 m). Deeper waters are dominated by Syringodium filiforme Kütz. and green algae. Intermediate and deeper waters contain fewer urchins and have higher plant diversities. Although highest plant diversities were correlated with intermediate grazer densities, the relationship is not causal. Instead diversity and community structure appear to be controlled more by light and competition than by grazing. Consumption rates of Lytechinus variegatus (Lamarck) on Thalassia are higher than previously reported, in the order of 5-6 cm3 day-1 or 0.6 g dry wt. day-1. The diet of these urchins appears to be governed primarily by availability and the palatability of food items. With the exception of Thalassia none of the common algae or seagrasses are taken preferentially. Detrital Thalassia and sediment are the two major food items in the diet. This feeding strategy minimizes the impact of urchin grazing on the structure and viability of Thalassia and the algal-seagrass community.

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Aquatic Botany, v. 14, p. 109-125