Herbivore abundance, grazing rates and feeding pathways on Australian temperate reefs inside and outside marine reserves: How are things on the west coast?

Abstract

Marine reserves are used as a management tool to conserve biodiversity and maintain ecological processes essential to ecosystem function. Grazing by herbivorous fish contributes to maintaining resilient reefs and marine reserves are important in conserving herbivores and their functional role. On the east coast of Australia, herbivores from the closely related families Girellidae and Kyphosidae are targeted by fishers and marine reserves have been shown to support greater size and abundance of girellids and kyphosids which enhances grazing on temperate reefs. On the west coast, however, kyphosids and girellids are rarely targeted by fishers. This study tested the hypothesis that there would be no difference in the size, abundance and feeding rates of girellids and kyphosids on temperate reefs inside and outside marine reserves at Rottnest Island, Western Australia, due to their relatively low levels of exploitation. The size, abundance and feeding rates of girellids and kyphosids inside and outside marine reserves were quantified using a diver-operated stereo-video system and feeding trials. No significant difference was found in the size and abundance of Kyphosus cornelii and Kyphosus spp. (Kyphosus sydneyanus and Kyphosus gladius combined) or feeding rates inside and outside marine reserves. The second aim of the study was to assess the relative importance of grazing and drift-feeding pathways used by kyphosids. Drift-feeding is an alternative form of herbivory to grazing and herbivores switching between grazing and drift-feeding pathways can have significant effects on algal communities, yet little is known about the relative importance of both feeding strategies for fish. A combination of feeding observations (mensurative) and feeding trials (manipulative) were used to quantify the number of feeding bites taken by fish on drift algae and attached algae. There was no significant difference in the number of feeding bites taken by the abundant herbivore, K. cornelii, on drift algae and attached algae during feeding observations, however, during feeding trials herbivores consumed significantly more drift algae (Ulva sp.) than attached algae. These findings demonstrate that drift-feeding is a common feeding strategy used by kyphosids. The findings in this study also highlight considerable differences in the effects of marine reserves on targeted east coast and non-targeted west coast populations of girellids and kyphosids on temperate reefs.