Ontogenetic variability in the habitat associations of Haliotis iris in central New Zealand

Abstract

The drivers of demographic variability in abalone are not well understood. Here, we examine ontogenetic variability in the habitat associations of black-foot abalone (Haliotis iris) populations in central New Zealand to better understand links between habitat variability and demographic variability in abalone. At larger, regional scales, there were west-to-east gradients in juvenile abundance, adult abundance and the size at which H. iris begin to occupy open reef habitats. At smaller, local scales, populations were depth-stratified, and there were two prominent transitions: a deep-to-shallow habitat transition during the juvenile stages; and a shallow-to-deep habitat transition during the adult stages. We also found that associations between abalone abundance and the size of the boulders, as well as associations between abalone abundance and the surface area of the interstitial spaces between boulders, differ among ontogenetic stages. For all stages, abundance was positively associated with crustose coralline algae cover, but negatively associated with articulated coralline algae cover. The relationship between canopy algae and adult abundance was positive, whereas for early juveniles, late juveniles and subadults, the relationship was weakly negative. Last, the association between the cover of understorey algae and abundance was negative for all ontogenetic stages. Overall, habitat variability played a strong, but ontogenetically variable, role in determining the abundance and distribution of H. iris.