Colour patterns in the sea urchin, Heliocidaris erythrogramma, suggest limited connectivity across the Southern and Pacific Ocean coastlines of Australia

Abstract

Heliocidaris erythrogramma is a widespread Australian sea urchin whose colour varies greatly. Here we report large-scale, hierarchically structured surveys, testing for patterns in colouration of H. erythrogramma associated with wave exposure, and consistency between populations from the Pacific and Southern Oceans. Along the Southern Ocean coastline, more urchins with white dermis were found in (ocean swell-exposed) open coast regions, whereas more urchins with red dermis were usually found in the (ocean swell-protected) bay regions. In contrast, only red dermis urchins were found in both open coast and bay regions along the Pacific coastline. Spine colour was found to be independent of test colour within locations and, while no differences in the frequencies of spine colours were detected between regions of different wave exposure, differences were detected across 1–100s of km within coastlines. Large differences in the frequencies of spine colours were also detected between the two coastlines. Clear differences in two independent characteristics of colour between Southern Ocean and Pacific coastlines, combined with intermediate patterns at a location near the junction of these coastlines, suggest that large-scale morphological patterns might reflect intra-specific genetic differentiation within H. erythrogramma, large-scale environmental differences between temperate Australian coastlines, or an interaction between these two factors.