Structural and environmental effects on an assemblage of echinoderms associated with a coral community

Abstract

Echinoderms are a conspicuous assemblage associated with coral communities, which provides them with food, shelter, and nursery areas. Temporal and spatial changes in environmental conditions may modify their density and composition, which furthermore may affect the structure of the coral community. In order to identify the response of echinoderm composition to environmental fluctuations, variations in the density were evaluated at spatial and temporal levels from 2011–2014 in Islas Marietas National Park, a National Protected Area located off the Mexican Pacific coast, which harbors the most important coral and echinoderm community in the region. The results showed that the species Diadema mexicanum, Centrostephanus coronatus, and Eucidaris thouarsii, were dominant. Differences between areas off the islands were observed, as Isla Redonda showed the highest values (1.31 ± 0.15 in. m2, \( \overline{S} \) = 7.74 ± 0.17) associated with high heterogeneity and availability of food resources. Isla Larga had the lowest density (0.89 ± 0.7 in. m2) and richness (\( \overline{S} \) = 6.49 ± 0.24). This was associated with the presence of high coverage of branching corals (16.34%) which can be considered a space competitor for echinoderms. Moreover, during cold seasons, density (17.44%) and richness (12.6%) increased, with a positive relation with the food supply. During the 2011/La Nina, a partial coral mortality resulted in the proliferation of turf and contributed to the highest abundance of grazer echinoderms. Abundance decreased during the following years, due to the loss of turf coverage. The assemblage of echinoderms maintained their species composition over the years, showing that the coral community of the Central Mexican Pacific has a singular auto-regulatory capacity that allows their long-term maintenance in response to environmental anomalies.