Abstract:
The aim of this study was to use an ecological modelling approach to explore the trophic interactions and size-based processes that underpin the green-lipped mussel reef ecosystem in the Hauraki Gulf, New Zealand. This information can be used to determine how the active restoration of these reefs could provide benefit to the wider Hauraki Gulf. An Ecopath with Ecosim (EwE) model was used to investigate the trophic interactions within the reefs. A community-based size spectra model was used to investigate the size-based processes within the reefs. The Size Spectra model also explored how enhanced structural complexity and invertebrate productivity associated with active reef restoration could impact overall ecosystem biomass and productivity. This exercise was the first time these model structures have been applied concurrently to a bivalve ecosystem and in the context of restoration. The sensitivity of both models was explicitly tested using a variety of methods and the models were found to be robust. Both models predicted that all functional groups would increase in biomass with active restoration, but they would recover at different rates. The EwE model also demonstrated the high complexity of trophic interactions within the reef benthic community. The Size Spectra model predicted that there would be a disproportionate increase in larger fish (>30cm), which would benefit fisheries. These models were based upon the best available information and the modelling process has identified knowledge gaps that can be used to guide future research. The model results can also be used to inform future restoration efforts and stakeholder expectations.