Simulating larval dispersal across the distribution of the New Zealand green-lipped mussel: insights into connectivity and source-sink dynamics

Abstract

Information about population connectivity, including the rates and routes of larval transport as well as source-sink dynamics, is important for the sustainable management of harvested species. For marine species whose primary mode of dispersal is transport during the pelagic larval stage, biophysical modelling of larval dispersal represents a valuable tool that is not subject to some of the same limitations as genetic connectivity analyses. In particular, a model that encompasses the entire distribution of a species can provide novel insights by identifying potentially important source populations or stepping-stone sites from which molecular samples may not be available. This study employed a Lagrangian particle-tracking model to simulate larval releases from all potential mussel habitats along ~15000 km of coastline for an endemic New Zealand bivalve, the green-lipped mussel. A northern and a southern cluster with a break near Cook Strait were identified, confirming the structure reported by earlier genetic analyses and a previous biophysical modelling study. The present study revealed, for the first time, that connectivity between the 2 clusters is largely asymmetrical, with more particle transport from the south to the north. Because this study simulated spawning events across the entire distribution of the species, several previously unknown source populations and stepping-stone populations were identified. These findings highlight the utility of a multidisciplinary approach to understanding marine connectivity and provide evidence for new strategies, including the protection of source and stepping-stone populations, to sustainably manage this endemic species.