Integrating EBM science to assess marine protected area effectiveness: clues from coral proxies of land disturbance, ecological assessments and socio-economic surveys

Abstract

Research for this study was carried out under a two-year project to support the implementation of Ecosystem-Based Management (EBM) at two catchment-to-reef sites on Vanua Levu, Fiji, during which period a pilot study was initiated to evaluate whether longlived coral records could be used to detect land-based disturbance to Fijian reefs. Trace element ratios of barium (Ba) to calcium (Ca) were measured at high (~weekly) resolution with laser ablation inductively coupled mass spectrometry (LA-ICP-MS) in cores collected from inshore and offshore Porites colonies. The Ba/Ca records from the inshore colony collected approximately 5 km south-east of the Yanawai River mouth and 3 km due west of the Nasue marine protected area (MPA) indicate heavy Ba/Ca enrichment between 1996- 1998, which may be related to high levels of sediment delivery to the nearshore while the Mt. Kasi gold mine was operational. Ba/Ca values from the offshore coral collected near the Namena MPA show consistently low baseline values during the same period and over the entire record. Underwater visual census (UVC) surveys of fish biomass, abundance and species richness from 2007 show significantly lower values inside the Nasue MPA than at adjacent sites open to fishing, while the opposite patterns are generally true for the Namena MPA. By synthesizing interdisciplinary data from multiple sources, deductive logic can be used to decipher major drivers of differences in effectiveness of the two district MPAs. Benthic survey data from Nasue closed and open areas showed no significant differences in specific factors which may indicate recent disturbance (e.g. macroalgal cover, rubble) and/or play strong roles in structuring reef fish communities (e.g. live coral cover, presence of fast growing branching corals, reef complexity). Therefore, we conclude that the historical disturbance from the Yanawai River either had minimal effect on benthic communities in Nasue MPA in sites surveyed or they have subsequently recovered and should therefore be able to support healthy reef fish populations if not subject to other types of disturbance. Socioeconomic surveys indicate that Kubulau residents are occasionally witness to infringements of MPA rules and the majority offenders come from outside the district. However, at the same time, Kubulau residents themselves have indicated catch locations within the Nasue (but not Namena) district MPA, suggesting that accidental or deliberate poaching occurs regularly, likely due to lack of awareness of MPA rules and boundaries and inability to see the Nasue MPA from the shore. Recommendations to improve the effectiveness of the MPA are discussed.