ABSTRACT: Size structure among 3 genetically distinct populations of the sea urchin Evechinus chloroticus was investigated between 1998 and 2007 at 22 study sites distributed in the Fiordland region in southwestern New Zealand. Data on morphology and abundance of the common kelp Ecklonia radiata was used as an indicator of the availability of high-quality food among sites. Habitats close to the fjord entrances with relatively high density of E. radiata (0.5 ± 0.1 [SE] to 1.2 ± 0.2 m^–2) supported E. chloroticus subpopulations with large average test diameters among years (94 ± 9.3 to 120 ± 2.8 mm) and stable adult modes across the 10 yr period. In contrast those subpopulations in inner fjord habitats with lower E. radiata abundance (0 to 0.4 ± 0.1 m^–2) were characterised by smaller average test diameters (64.3 ± 6.5 to 103.4 ± 1.7 mm) and frequent large pulses of newly emergent juveniles (<60 mm). These patterns in demographic variability were apparent in an index of recruitment, which increased from the kelp-dominated outer coast to the marginal inner fjord habitats. In the 10 yr period, complete adult mortality events were observed at 5 sites in inner fjord habitats, followed by re-colonisation by newly emergent juveniles. The data suggest that population networks arranged across gradients of habitat quality are more likely to exhibit rescue effects and to maintain higher abundance in marginal habitat than are isolated populations. These results highlight the importance of including core source populations in marine reserve networks for regional persistence and stability of marine metapopulations.