3.2.2c Trophic effects through herbivory at Ningaloo Reef

Description

This project aimed to characterise plant-herbivore interactions in the Ningaloo Reef Marine Park, and has provided the first quantification of the process of herbivory in this region. In doing so, it has provided key information to answer the management questions identified in the Ningaloo Research Program Research Priorities.

Aims

• Determine the species diversity of key flora and fauna in selected representative habitats
• Determine is the abundance, size composition and distribution of these key species
• Determine whether variations in predator abundance indirectly affect reef ecosystem structure including the abundance of grazers, algae and corals and corallivorous gastropods (Drupella)
• Establish if current management arrangements/regulations appropriate for preserving the biodiversity represented within the park

Methods

• Field Surveys.
• Underwater visual surveys, Swimming Transects
• Quadrat sampling
• Transplant experiments; caged and uncaged plots for herbivory quantification
• Herbivory rates, timed mass loss of algae samples across habitats
• Underwater video camera UVC surveys
• PERMANOVA, nMDS,
• Tissue sampling

Outcomes

• A baseline survey of all nominally herbivorous fish species (fish density and quantitative feeding activity data) across a range of regions  has been completed and key species that should be closely monitored have been identified.
• Evidence has been provided that structural complexity is a key factor influencing herbivory. Conservation efforts should thus focus on conserving this trait (e.g. protect coral habitats from anchoring damage).
• Quantitative data has been gathered that can be used to support potential management plans aimed at protecting herbivorous fishes from exploitation on the basis of their critical role for promoting coral-reef resilience.
• A direct comparison of herbivory between different coral-reef systems, indicates that Ningaloo Reef is a comparatively pristine system.
• Herbivory is a dominant mechanism that influences the abundance of fleshy macroalgae when recruitment space is equal in the lagoon and reef-flat habitats. Zoning needs to consider the movement of key herbivores across habitats when determining boundaries of management zones.
• Monitoring the biomass of Naso unicornis, Kyphosus spp. inside and outside sanctuary zones will provide crucial information of the potential influence of zoning on macroalgal removal in the NMP, as well as a region’s ability to recover from disturbances that enhance macroalgal production.
• Quantitative data on rates of herbivory from our studies can be incorporated into broad- scale fish density data from other projects to model the effects of disturbances and changes in management strategies on herbivory, and potential effects to the system as a whole.
• Data on the spatial patterns of movement are needed for all key macroalgal grazers to ensure that sanctuary zones preserve their abundances.
• Research is needed to further investigate the potential for indirect ecological effects and trophic cascades through the removal of higher order predators (e.g. sharks) in the NMP .