Differences in population connectivity of a benthic marine invertebrate Evechinus chloroticus (Echinodermata: Echinoidea) across large and small spatial scales

Abstract

Marine organisms with a planktonic larval stage have the potential to be transported substantial distances, with the distance travelled depending on factors such as pelagic larval duration (PLD) and physical factors such as ocean currents and geographical barriers. The endemic New Zealand sea urchin, Evechinus chloroticus, is found throughout the North and South Islands, and with a PLD of approximately 30 days, is expected to show strong connectivity among all populations. Population connectivity and genetic differentiation were examined over both a geographically broad scale, throughout New Zealand, and on a fine scale (within the Hauraki Gulf on the North Island). Significant genetic differentiation was revealed through analysis of mitochondrial COI sequences (FST = 0.096 p < 0.01) and six microsatellite loci (FST = 0.0120 p < 0.008). This was consistent with a division between northern and southern regions located to the south of Cook Strait, at a phylogeographic barrier previously reported in other New Zealand benthic marine invertebrates. Fine-scale population differentiation was evident between the inner and outer Hauraki Gulf populations, and between the most northern populations and the remainder of the North Island. Together, this study suggests that strong coastal currents, upwelling in the Cook Strait region, and geographic distance (approximately 2000 km north to south) may all be acting to restrict gene flow and contribute to genetic divergence among populations of E. chloroticus.