Variation in abundance and spatial distribution of ecomorphs of the sea urchins, Echinometra sp. nov A and E. sp. nov C on a Fijian reef

Abstract

This paper presents novel spatial distribution and abundance patterns of ecomorphs of Echinometra sp. nov A andE. sp. nov C (hereafter referred to as E. sp. A and E. sp. C, and collectively as Echinometra spp.). Echinometraspp. were surveyed on the Nukubuco Reef, to determine the within-reef variations in size-frequency and density atseveral spatial scales [between positions (east versus west), zones (crest versus flat), sites and quadrats]. The scalesof variation were greatest for both species between positions and zones. Echinometra sp. A was more readily foundon the calmer flats while E. sp. C preferred the high-energy crests. The distribution of ecomorphs of Echinometraspp. varied between habitats (position x zone). Echinometra sp. A ecomorphs were more abundant on all locationsand showed different size-class distributions compared with E. sp. C. Greater urchin numbers were observed onboth zones of the eastern position than the western position. Echinometra sp. A showed marginal aggregationpattern while E. sp. C showed a stronger tendency to cluster.