Early life ecology of Haliotis iris: the effects of algal habitat depth and substrate complexity on recruitment

Abstract

The demographic consequences of recruitment processes are intimately dependent upon the habitat experienced by larvae and early juveniles. Quantitative surveys of Haliotis iris populations revealed strong habitat-specific associations throughout their ontogeny. The architecture of the surrounding algal habitat had strong significant effects on the density of settlement, subsequent post-settlement mortality and early juvenile predation. Simplified barren habitats had significantly greater densities of settlement, however increased rates of post-settlement mortality and early juvenile predation subsequently modified patterns of settlement. Results of this study suggest continued increases in the spatial distribution of barren habitats via the destructive grazing of urchins may have long-term negative effects for the recruitment of abalone. Populations were depth stratified with reciprocal length-dependent depth transitions. The discontinuous juvenile depth distribution suggests a rapid transition from deep (6-9m) to shallow (<1m) habitats between the early (<10mm shell length) and late juvenile (11-70mm shell length) stages, followed by a gradual transition back to deeper habitats as adults (ώ71mm shell length). Settlement of H. iris was homogeneous among depths with shallow and deep habitats receiving equal supply of settlers. Early juvenile predation was also unaffected by depth. While post-settlement mortality experiments were confounded by an artificial enhancement in shallow habitats, the consistency of depth-specific patterns of early juvenile abundance suggest, the mechanisms driving this pattern may have strong effects on the demographics of abalone populations. H. iris occupied the interstitial spaces provided by complex cobble/boulder habitats throughout the juvenile stages (~75mm). Cryptic habitats provide a predator refuge for juvenile abalone and results of this study suggest the availability of suitable cryptic habitats may be a leading determinant of abalone recruitment success.