Lobsters as keystone: Only in unfished ecosystems?

No-take marine reserves (MRs) are a useful tool to study the ecosystem effects of fishing as many MRs have allowed ecosystems to recover to pre-fished states. Established in 2008, the Taputeranga MR, located on the south coast of Wellington, New Zealand, provides full no-take protection to the nearshore marine environment. Commercial, recreational, and customary fisheries are important in this region and commercial catch records for the last 70 years indicate that exploitation has greatly reduced the biomass of some species. We employed an ecosystem modelling approach to analyse the food web linkages on this coast immediately prior to MR establishment (the pre-MR state) for comparison to reconstructed historical and predicted future ecosystem states. Our results suggest that the organisation and function of the pre-MR ecosystem have changed since the 1940s, notably in terms of the role played by lobster (Jasus edwardsii). Historically, lobster were at least four times more abundant, and played a keystone role by directly negatively impacting the abundance of prey species, and indirectly positively influencing the abundance of the prey of their prey. While the fishery for lobster that operates today is well managed and sustainable from a single-species perspective, our results indicate that the fishery has reduced lobster biomass sufficiently to have significant impacts on the organisation and function of the nearshore temperate reef ecosystem along Wellingtons's south coast. Our results predict that over the next 40 years, the Taputeranga MR is capable of restoring the protected ecosystem to a state more similar to that observed in the past, prior to large-scale commercial exploitation. This finding has implications for the management of fisheries in other areas, as we have demonstrated the inability of the single species fisheries model to manage the ecosystem effects of fishing.