The southeastern Australian Point Conception: Supply-side ecology for a marine invertebrate approaching its geographic range limit

The supply and recruitment of larvae can be important determinants of the size of local populations for many marine species. It might be predicted that, under an abundant-centre geographic distribution, adult abundance and recruitment from the centre to the limit of the range will be tightly coupled for species with relatively closed population dynamics and uncoupled (or weakly coupled) for those with open population dynamics. To examine these predictions and the degree of connectivity among local populations for a species of barnacle with a relatively long planktonic duration, we quantified adult abundance and recruitment at multiple locations and spatial scales across 600 km of coastline from the centre of its range in Sydney to the southern limit of its georgraphic range in south eastern Australia. Adult abundance and recruitment both declined from the centre to the limit of the range and, consequently, were strongly and positively correlated at this large, geographic spatial scale. In contrast, at smaller spatial scales (e.g. within locations) along the geographic range, there were few significant relationships between adult abundance and recruitment. Consequently, the degree to which local populations are replenishing themselves at relatively small spatial scales is difficult to ascertain, but it is clear that local populations at the limit of the range are not being extensively replenished from more central populations.