The sea urchin Echinometra lucunter (Echinodermata, Echinoidea) as a refuge for the barber goby Elacatinus figaro (Perciformes, Gobiidae)

Abstract

Elacatinus are small bright colored reef fish that have the habit of cleaning fishes and invertebrates. Elacatinus figaro are often found near the sea urchin Echinometra lucunter, suggesting a possible relationship between them. The addressed questions of this study are: (1) is the territory occupied by E. figaro related to the proximity of E. lucunter?; (2) does E. figaro show a refuge preference for E. lucunter spines?; and (3) are the densities of the two organisms correlated in the studied rocky reefs? Quadrats (1.0m2) were randomly sampled in three rocky reefs in Arraial do Cabo, RJ, Brazil. Before placing each quadrat on the substrate, the distances between each of the 89 E. figaro individuals observed and their nearest urchins were registered. While placing each quadrat, the escape behavior and the chosen refuge were observed. Furthermore, the densities of E. lucunter and E. figaro in each quadrat were quantified. From all observed E. figaro, around 57% were inside the perimeter of the urchins’ spines, 21% were less than 10cm far from them, 17% were between 10cm and 20cm away from them and less than 5% were more than 20cm away from the urchins. Most of the E. figaro (around 95%) that were out of the urchins spines’ perimeter promptly moved to the nearest urchin during the quadrat location. A positive correlation was observed between the densities of E. lucunter and E. figaro, suggesting a strict association between them, probably due to the use of the spines of the sea urchin as a refuge by this goby.