Spatial Abundance and Colour Morphotype Densities of the Rock-Boring Sea Urchin (Echinometra lucunter) at Two Different Habitats

Abstract

The rock-boring sea urchin Echinometra lucunter is a common echinoderm found throughout the intertidal zone along the northeastern coast of, Toco, Trinidad. Sea urchin abundance, size distribution, and colour morphotypes at two sites: Pequelle Bay (SB) and Grande L’Anse (GA) were quantified using 1 m2 quadrats, accessible during extreme low tides, and in two environments, notably low and high wave action. Percent coverage of cnidarian and macroalgae were estimated in each quadrat. Sea urchin densities were 9.9–17.8 urchins/m2 in high wave action, and 25.2–60.7 urchins/m2 in low wave action environments. Size (measured as maximum sea urchin diameter) are highest between 21 and 50 mm for both black and red colour morphotypes. Black colour morphs were significantly larger than red morphs (ANOVA, F2, 175 = 5.55, p < 0.05). Sea urchins at low energy environments were significantly larger than those found in high energy environments for all years (p < 0.05). Mean hard coral, soft coral, and macroalgae cover did not show any relationship with habitat type or urchin densities. Although sea urchin abundance and distribution were variable, larger urchins were more likely to be found in low wave action environments, and smaller urchins were mostly found in the open, and exposed to high wave action.