The identification of juvenile Haliotis iris habitat within the east Otago Taiāpure

Abstract

The role of nursery habitat to the distribution and abundance of abalone fisheries globally is poorly understood. The New Zealand abalone, Haliotis iris, is a species of cultural, recreational and economic importance which has been showing signs of decline. The aim of this study was to identify the distribution of H. iris nursery habitat within the East Otago Taiāpure (EOT), a locally managed fishery, and assess the impact of major current and future threats to juvenile H. iris. The results from this study estimated the density of juvenile H. iris at the major reefs within the EOT for two levels of wave exposure and three depth ranges. Furthermore, correlations were made between the abundance of juvenile H. iris and several biotic and abiotic variables, which were used to define juvenile nursery habitat. Several sites of suitable juvenile H. iris habitat within the EOT were found to contain no individuals indicating habitat is not a limiting factor. The distribution of juvenile H. iris was found to be tightly linked to the abundance of adult H. iris, indicating that recruitment is localised, on the scale of meters to tens of meters and the areas of suitable habitat with no inhabitants may be recruitment limited. The information gained from this study was used to guide a reseeding programme, identifying areas limited by recruitment to be reseeded. This study also investigated how increases in sedimentation affected juvenile H. iris abundance, distribution and interspecific relationships. It was found that sedimentation had a negative effect on juvenile H. iris survival and no effect of competition with Chiton glaucus, a common resident of intertidal cryptic habitat where juvenile H. iris, was found. Increased sedimentation due to land use changes may cause juvenile H. iris be displaced by more sediment tolerant species, such as C. glaucus. As atmospheric CO2 increases over the next 100 years the carbonate saturation state and pH of temperate surface waters will decrease possibly resulting in limited shell formation and dissolution for marine calcifiers such as H. iris. It was found that both juvenile and adult H. iris possess a pH microenvironment at their surface termed the concentration boundary layer CBL. Neither juvenile nor adult H. iris were capable of modifying the internal environment to mitigate the effects of ocean acidification (OA), both must rely on other protective mechanisms which may be influenced by current changes to sedimentation. Information gained from this study may be used to better manage the H. iris fishery within the EOT at an appropriate scale by understanding the spatial distribution of juvenile H. iris and the associated habitat, as well as understanding the effects of increased sedimentation and OA on survival.