Evaluating the efficacy of small‐scale marine protected areas for preserving reef health: A case study applying emerging monitoring technology

Abstract

1. Marine Protected Areas (MPAs) are widely used as management tools to conserve species and ecosystems at risk from human impact. Coastal managers often focus MPA designation on biogenic reef environments due to their value and sensitivity to damage. However, difficulties in enforcement and a lack of capacity to adequately monitor MPAs often make it hard for managers to assess the effectiveness of MPAs, particularly in under-resourced, low-income coastal countries. 2. Reef community data were collected at three long-term managed reserves within the Western Visayas region of the central Philippines in order to assess the state of reef community structure inside and outside of these small-scale locally managed MPAs. In addition, 3D structural data were captured using recently developed 'Structure from Motion' (SfM) photogrammetry techniques, demonstrating how multiple quantitative metrics of physical structural complexity and health can be recorded in such analyses. 3. These community-run MPAs were shown to be effective even when small (10-20 ha). Mean fish biomass density was five times greater within present-day protected sites, alongside significantly increased levels of fish diversity, richness, and size. No significant structural differences were observed inside and outside of MPAs, however, average reef rugosity, height, and roughness were significantly higher in unfished reefs compared to blast-fished reefs. Reef substrate complexity, coral composition, and level of management, were also shown to structure fish community assemblages, with the link between reef structure and fish richness / abundance disrupted outside of MPAs. 4. The SfM technique allows a greater range of quantitative morphometrics to be assessed than traditional methods and at relatively low cost. The technique is rapid, non-destructive and can be archived, increasing the value of data for managers wishing to quantify reef health and efficiently monitor benthic changes through time. We discuss both the limitations and benefits of this technology's future use.

Measuring the long-term success of small-scale marine protected areas in a Philippine reef fishery

“…Changes in coral cover through time at the site level were only significant at Bilangbilangan (seeing a significant increase in cover inside the MPA) and Pandanon (seeing a Coral Reefs significant decrease in cover inside the MPA). These observations match well to other studies of this reef system which found Bilangbilangan to be relatively well managed, whereas Pandanon was seen to have regular systematic blast fishing occurring (even inside the MPA limits at points in the reserve's history), causing loss of structure and a hampered recovery due to the resultant mobile rubble substrate (Samoilys et al 2007;Bayley et al 2019).…”

“…Any differences in cover were instead largely driven through site-level heterogeneity. The fishing methods in this localised region therefore appear to typically not be permanently damaging to the benthos, unless intensive localised blast fishing is employed, such as at the site 'Pandanon' within this study (Selgrath et al 2018;Bayley et al 2019).…”

“…Fish biomass estimates were calculated for each family using the standard weight-length relationship (Froese 2006), where W = a L b , with the values of constants a and b based on species-specific calculations obtained from Fishbase (Froese et al 2014; Froese and Pauly 2018) using the Rfishbase() web-interface package in R. Given that the fisheries data were collected at the family taxonomic level, we pooled size-based growth values for all species known to occur in this region (Bayley et al 2019) and then used the mean values for the family averaged groups.…”

“…Declines in fish density were most pronounced for larger fish (20-40 cm), both inside and outside of MPAs. These declines in commercially valuable size classes both inside and outside of protected areas could indicate potential infractions into the protected sites, such as at the Batasan MPA where the site guardhouse was noted to have been damaged, or at Pandanon where evidence of heavy blast fishing has been observed both inside and outside the MPA (Bayley et al 2019). While small MPAs can be effective for the protection of mobile species (Claudet et al 2010), the observed declines of larger fish in this study could also indicate an important limitation to these very small areas, which are typically less than the 2 km minimum diameter suggested for even partial protection of most reef fishes (Krueck et al 2017).…”

“…These increases in size and capacity may be particularly effective in existing sites such as Pandanon, Jandayan Norte and Handumon, which are heavily exploited and closest to dense populations of people and fishery markets/ports (i.e. close to Cebu city and Northern Bohol) and have shown continuing rapid present-day declines in fish biomass or benthic cover (Cinner et al 2018;Bayley et al 2019). Without these improvements, it is unlikely any local benefits will be sustained by the small sites, and instead population gains will leak out or be encroached upon by the unmanaged and exploited surrounding region.…”