Recruitment and recovery of pink abalone (Haliotis corrugata) in a historically overexploited kelp forest: Are local populations self-sustaining?

Abstract

After experiencing a reduction in density, many populations of benthic, broadcast spawning marine invertebrates have struggled to recover or have collapsed. Genetic techniques may help to distinguish populations that are self-sustaining from those at risk of further decline, and demographic interdependence among subpopulations. We tested the use of genetic data for identifying stable and self-sustaining abalone populations, as well as the efficacy of a restoration technique for use in those populations that are not. We created an artificial aggregation of wild adult pink abalone (Haliotis corrugata) in the Point Loma kelp forest near San Diego, CA, USA. We genetically analyzed those individuals and additional adults and juveniles in the broader region. A self-sustained population should not be demographically reliant upon immigration. Temporal variability in relatedness among juvenile cohorts, and a lack of fine-scale spatial structure in adult and juvenile relatedness indicated complex recruitment dynamics and/or long distance larval delivery. We estimated a low effective population size (Ne=188) and a very low ratio of effective population to census population size (Ne/N=2.0×10−3). These data are consistent with sweepstakes reproductive success, and suggest that the population is at risk of genetic diversity decline. Parentage assignment revealed that none of the juveniles sampled one year after aggregating adults had parents from this aggregation. Collectively, our results suggest that restoration efforts will need to achieve a greater density (0.18m−2) and/or number of individuals (46) to improve local recruitment. Our results also suggest that the Point Loma kelp forest population of pink abalone is of insufficient density for long-term viability, may be reliant upon immigration, and cannot be defined as an independent “local” population unit.