How far can marine species go? Influence of population biology and larval movement on future range limits

The range of a marine species varies with a wide range of factors including temperature, currents, interspecific interactions and available habitat. Invasive species offer insights into the processes that influence range expansion because they are in the initial stages of an expansive period. We modelled the range expansion of an invasive seastar with an extended larval period throughout southern Australia using a linked physical and biological model. We found that the establishment of new populations was dependent on larval supply and, critically, on the ability of new habitats to retain larval production within the local habitat to compensate for Allee effects at low population densities. Larval supply from existing populations determined the locations of invasions, whereas local retention of larvae determined how fast and how large a population could grow. Increased diffusion dispersed larvae to areas otherwise inaccessible to them in a purely advective model, and had the potential to increase establishment probabilities. Range extension progressed as new populations were established downstream of source populations in locations where the retention of locally produced larvae was sufficient to generate long-term positive growth rates.