Monitoring Coral Reef Communities in Hawai‘i’s First Herbivore Protection Area
North Kāʻanapali, West Maui, Hawai‘i
In the summer of 2009, the state of Hawai‘i established Hawai‘i’s first MPA designed entirely to promote resilience, the Kahekili Herbivore Fishery Management Area (KHFMA), in which take of all herbivores (parrotfish, surgeonfish, chub and urchins) and fish feeding is prohibited, but other forms of fishing are permitted. The establishment of the KHFMA provides a test case for the prohibition of fishing of herbivores on Hawai‘i’s reefs. Compelling evidence of its effectiveness could lead to wider adoption of this form of management and/or additional fishing regulations. As an example, in 2014, the state of Hawai‘i introduced a bag limit of two parrotfish per fisher per day and no take for terminal phase of the two largest parrotfish species for reefs in Maui, in part, due to evidence that came from the KHFMA monitoring project. In Hawai‘i, as in other parts of the world, fishery regulations and marine protected areas are contentious. Therefore, both supporters and potential critics of these management approaches are carefully observing the outcomes of the herbivore management.
Early in the process of establishing the KHFMA, Hawai‘i Division of Aquatic Resources (DAR) and partners at the University of Hawai‘i established a long-term monitoring program within the proposed MPA boundaries to gather data to provide a pre-closure baseline for the KHFMA. The first surveys occurred in January 2008, 18 months prior to the establishment of the reserve. The monitoring program consists of intensive biannual surveys conducted by DAR and NOAA’s Coral Reef Ecosystem Division.
The survey design involved subdividing the habitat within the reserve into 6 habitat categories based on physical structure and depth (shallow aggregate reef, deep aggregate reef, shallow spur-and-groove, deep spur-and-groove, pavement, and mixed mid-depth), that also corresponded with location along the shoreline and with proximity to shore. Within each habitat class, pairs of divers surveyed 25m-long transects haphazardly located, with one diver surveying fishes and the other conducing a photo-transect survey and also recording numbers of sea urchins on their return swim. Typically, dive teams completed 90-100 surveys in each 4-day monitoring round, images are subsequently analyzed, and all fish, urchin, and benthic data is synthesized within habitat classes and at the scale of the KHFMA, with each habitat weighted by its relative size.
How successful has it been?
In September 2014, 5 years after establishment of the KHFMA, results to date indicate strong evidence of herbivore recovery. There has been more than doubling of parrotfish biomass, particularly increases in numbers of large individuals, and there has been an increase in parrotfish diversity, particularly in shallow habitats that likely were most heavily fished prior to closure. Surgeonfish biomass has also increased significantly, but to a lesser degree. Over the same time period, cover of crustose coralline algae (CCA), considered indicative of high grazing pressure and which is suitable substrate for coral settlement and growth, has increased from 2% cover pre-closure to >10% cover after 5 years of protection. Coral cover has also begun to increase within the KHFMA over approximately the last 18 months, but the increase thus far is relatively small. See the related Case Study on the Kahekili Herbivore Fisheries Management Area for details on actions taken and lessons learned from managing the area for reef resilience.
Therefore, preliminary evidence suggests that herbivore protection is working; grazing pressure has increased and as a result, the competitive balance has shifted from algal to coral dominance following a long period of decline on local reefs.
The ability to produce high quality data showing recovery has been very important in maintaining public and broader support for the KHFMA. Additionally, the ability to separate out patterns of recovery in different areas of the reserve has been very helpful in understanding factors such as the likely degree of compliance. For example, in the first two years of protection, although there was clear recovery in deeper habitats, there was initially little change in the shallow fringing reef areas close to parking facilities, and therefore, most vulnerable to poaching. Certainly some poaching occurred in the first years after closure. However, compliance appears to be improving, based on data indicating strong recovery in those areas and reports from a motivated and engaged community.
Lessons learned and recommendations
A strong partnership involving an active local management agency (DAR) with strong links in the community has been fundamental to ensuring that the positive monitoring results have been widely disseminated.
As is common in Hawai‘i, the reefs in the KHFMA are highly variable, encompassing a wide range of habitat types and habitat quality. Therefore, we designed a survey strategy to maximize the number and spatial spread of transects within the KHFMA to increase confidence that the results are representative of the entirety of reef habitats within the reserve. There are trade offs in all design decisions, but key choices were made to:
- haphazardly locate transects rather than utilize permanent transects. Data from permanent transects would have lower variability between survey rounds, but with significant overhead to install and maintain them, and even to locate them in the course of survey dives; and
- develop a habitat map of the KHFMA reef, with all reef areas stratified into the habitat classes described above
The habitat map simplifies the program operationally because it allows divers to conduct as many transects as possible within each dive, then use the transect locations to classify each transect into one of the pre-defined habitat categories. We could then generate summary data per survey round separately for each habitat class and for the KHFMA as a whole. That allowed us to discern the different trajectories of recovery in the different habitat zones due to different species compositions, history of fishing, and degree of local compliance.
Another key lesson is that sampling multiple times a year is important because of strong seasonal differences in macroalgal cover. We sampled in spring and late summer each year. More regular sampling would be desirable, but would be operationally challenging because each of our sampling events involves bringing together teams from different islands (Oahu and Maui) and agencies which have other priorities and programs.
It is important to measure change over time within the reserve, but it is also necessary to compare those trends with patterns occurring on comparable reefs outside the reserve. The state of Hawai‘i has long-term monitoring programs at 8 reef areas in Maui. Although the survey design for that long-term monitoring was not exactly the same, the methods used are compatible. We used data from the KHFMA to measure change over time within the reserve and used the existing long-term monitoring data for ‘outside-MPA’ comparisons. While there are some drawbacks to that (e.g., inside and outside reserve data are gathered using different methods and survey designs), the benefit is that we did not have to establish specific KHFMA controls for this project, and therefore were able to focus all our survey effort on the KHFMA rather than dividing it between two (KHFMA and one control) or three or more areas (KHFMA and two or more controls).
As with nearly any new monitoring program, there are enormous potential benefits from being able to compare and share data with other local programs. Therefore, we strongly advise anyone establishing a new program to adopt methods and ideally designs that are widely utilized in the region. More generally, increased data sharing across programs is critical given the difficulty and cost of gathering coral reef survey data. In Kahekili, the availability of abundant high-quality local data has contributed to the scientific focus on the KHFMA – researchers wishing to study the region make use of the rich dataset available to them.
Finally, although preliminary evidence demonstrates the effectiveness of the KHFMA, there is still a long way to go before the full extent of reef recovery may occur. Herbivore biomass is increasing 5 years post closure, yet studies elsewhere have shown that reef fishes can take 10 or 20 years post closure to reach new maxima (surgeonfish being particularly slow to fully recover, perhaps because of their long life spans). Further, although increased herbivory does appear to have generated conditions more suitable for coral recruitment and growth, the relatively slow growth of corals means that it will be a long time (e.g., 10-15 years or more) before ultimate impacts of herbivore protection on coral assemblages are fully evident. Survey programs aiming to measure the effectiveness of herbivore management should therefore (i) expect that full recovery will be a process of decades not years; and (ii) ideally incorporate process studies (e.g., coral recruitment growth and mortality) to have the greatest scope for early detection of positive impacts. Although we have attempted to initiate such studies at KHFMA, we have not yet been successful in raising funds for that work.
Hawai‘i Coral Reef Initiative Research Program
NOAA Coral Reef Conservation Program
Hawai‘i Division of Aquatic Resources, Department of Land and Natural Resources
NOAA Coral Reef Ecosystems Division, Honolulu