Population density of four species of sea urchin Echinodermata Echinoidea at La Entrega Reef, Oaxaca Densidad poblacional de cuatro especies de erizo Echinodermata Echinoidea en el Arrecife de La Entrega, Oaxaca

Zamorano, P.; Leyte-Morales, G.

Oceanides 20(1-2): 65-72

2005


ISSN/ISBN: 1560-8433
Accession: 038554349

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Abstract
Bimonthly samples of sea urchins fauna inhabiting the La Entrega Reef, Oaxaca, Mexico, were obtained from October 2002 to August 2003. The reef area was divided in two sampling zones, corresponding to shallow (0-6 m) and deep (6-12 m) water. Six transects of 50 m length by 1 m wide were sampled in each zone. Greatest annual density corresponded to Diadema mexicanum (5.96 plus or minus 0.85 ind/m2), followed by Eucidaris thouarsii (0.46 plus or minus 0.14 ind/m2); Echinometra vanbrunti and Toxopneustes roseus presented low densities (0.03 plus or minus 0.01 indv/m2 and 0.02 plus or minus 0.01 ind/m2, respectively). Density of the four populations varied considerably and higher densities were observed in the deep zone. Total abundance of sea urchins (shallow and deep samples) did not vary significantly over time. Abundance per depth range, however, was different over time for all species except for E. thouarsii. In December densities of D. mexicanum and E. thouarsii decreased in the deep zone and increased in the shallow zone, due to massive mortality of coral in the shallow part of the reef and to subsequent increase of algal coverage attracting these species to the shallowest part of the reef. The La Entrega reef is presently in an advanced state of erosion that could favor an increase of sea urchins abundance and of their bioerosion activity.