Fine-scale habitat change in a marine reserve, mapped using radio-acoustically positioned video transects

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Abstract
Large-scale changes in subtidal reef habitats have occurred within the Leigh Marine Reserve (New Zealand) since its establishment in 1976. To determine the extent of habitat change within Goat Island Bay, video transects positioned by a radio acoustic positioning telemetry (RAPT) system were used to map habitats within a Geographic Information System (GIS) framework. This map was compared to a map of the same area constructed 22 years earlier in 1978. Visual categorisation of habitats was consistent with the quantification of habitat-forming species within quadrats, justifying the creation of a map based on visually interpreted video footage. Furthermore, the large-scale changes in habitats were consistent with smaller-scale changes in community structure identified at permanent sites located in the study area. The most obvious changes were the total disappearance of ‘urchin barrens’ across all depths and the recovery of kelp forest in water 12 m, the extent of kelp forest and sponge flats was found to decrease by 25 and 33%, respectively, while turfing algal habitat had increased by 50%. This increase in turfing algal habitat had not been previously documented due to the spatial scale of traditional sampling methods.