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An Integrated Coral Reef Ecosystem Model to Support Resource Management under a Changing Climate

Ecosystem-based management is a useful management tool that considers both indirect and cumulative effects of added stressors to a system. Ecosystem models, especially those that consider physical and biological disturbances and human uses, can help to inform ecosystem-based management during planning and implementation stages. This study modified the Atlantis Ecosystem Model to quantify and predict the effect of added stressors on the Guam coral reef ecosystem. Specifically, the study focused on three main stressors: climate change, land-based sources of pollution (LBSP), and fishing. The study used the IPCC Fifth Assessment Report highest emission scenario to predict atmospheric COconcentrations and the RCP8.5 projection to predict sea surface temperatures. LBSP was predicted using previous data collected on Guam’s sediment and nutrient loads and river flow. Fishing predictions were based on historical catches. Short term (i.e. 30 years) and long term (i.e. 65 years) simulation tests were run for each stressor.

The short term tests revealed that fishing resulted in the greatest negative impacts with LBSP following close behind. Climate change became the dominant stressor in longer time scales with the bleaching threshold exceeded every year after year 48. It becomes clear that long-term high intensity disturbances from multiple stressors limits and sometimes even prevents ecosystem recovery. Limiting frequency, intensity, and number of stressors can significantly increase reef resilience. This study revealed that reducing LBSP and increasing water quality can delay climate-related impacts for up to 8 years while buying time for the corals to adapt to higher temperatures. The Atlantis Ecosystem Model and others like it can be used to provide a wealth of knowledge to inform ecosystem-based management decisions on both regional and global levels.

Author: Weijerman M., E.A. Fulton, I.C. Kaplan, R. Gorton, R. Leemans, W.M. Mooij, and R.E. Brainard
Year: 2015
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PLoS ONE 10(12). doi: 10.1371/journal.pone.0144165

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WE ARE 10!!!

Can you believe it? A decade ago, TNC – with the support of partners AROUND THE WORLD– launched the Reef Resilience Network, creating what would grow to become a global network of resource managers sharing ideas, experiences, and expertise to effectively manage our coral reefs and reef fisheries. Curious to see what ten years can do for managers and reefs? Take a look below and here!

RRonline

Special thanks to NOAA’s Coral Reef Conservation Program, Great Barrier Reef Marine Park Authority, and International Union for Conservation of Nature, whose committed support to the Network has helped managers innovate, accelerate, and leverage solutions for improved global coral reef health and restoration of reef fisheries.

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Coral Reef Disturbance and Recovery Dynamics Differ Across Gradients of Localized Stressors in the Mariana Islands

Disturbance and recovery patters of coral reefs in the Commonwealth of the Northern Mariana Islands were studied over a 12-year period, including Crown of Thorns Starfish (COTS) densities, localized stressors, and natural disturbances such as tropical storms. COTS densities caused significant coral decline, however, the ability of reefs to recover was most influenced by localized stressors, in particular, grazing urchin densities and herbivore sizes. Reefs on Saipan had the highest disturbance impacts, with smaller fish sizes, grazing urchins, and water quality, even though they had the most favorable geological features for coral growth. These reefs are also subject to reef-based tourism, which is important to CNMI’s economy and thus deserves a hard look at how to improve fish assemblages, urchin populations, and local water quality concerns.

Author: Houk, P., D. Benavente, J. Iguel, S. Johnson, and R. Okano
Year: 2014
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PLoS ONE 9(8): e105731. doi:10.1371/journal.pone.0105731

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Behind-the-scenes on Project REGENERATE

Photo © Project REGENERATE

In recent years, the IUCN has increased its engagement in the Maldives, a group of islands in the Indian Ocean, with the development of the IUCN Maldives Marine Projects program, which aims to support the Government in addressing the environmental priorities and challenges that the Maldives faces. Project REGENERATE (Reefs Generate Environmental and Economic Resilience in Atoll  Ecosystems), a major project under this program, supports the sustainable management of coastal resources in the Maldives, particularly coral reefs, in order to build economic, social, and environmental resilience to the adverse effects of climate change. One major research activity of the project is a two-leg scientific expedition to investigate coral reef biodiversity and resilience and provide baseline ecological data for the Maldives.

The first leg of the expedition, in collaboration with the University of Queensland and the Catlin Seaview Survey, employed high tech cameras to collect data from eight atolls. The second leg of the research cruise was comprised of 17 researchers, representing  universities, research and environmental institutions from around the world, and focused on North Ari (Alifu Alifu) Atoll in the Maldives. The team documented fish abundance and species structure, benthic composition, coral population demographics, coral bleaching and disease, mobile invertebrate species, and foramnifera health. A key strategy of the project was to build local capacity by training citizen scientists in national monitoring protocols. Citizen scientists from Alifu Alifu Atoll, the capital Male and as far afield as Colombo, Sri Lanka, joined the research team, received training, and helped to collect data for their home reef. The data collected will help to assess the resilience of the coral reef ecosystem. It will also help to assess how population density affects reef health. Such assessments address important data gaps in the region and are critical in a country highly vulnerable to climate change, and also dependent on its world-renowned coral reefs and the resources that they provide. This information, combined with data from future monitoring assessments, will inform policy and management decisions in the region.

The Reef Resilience Team got a “behind-the-scenes” glimpse into this expedition from two crew members: Zach Caldwell, The Nature Conservancy’s Dive Safety Officer, and Amir Schmidt, IUCN Maldives Marine Projects Field Officer.

Reef Resilience (RR): Can you tell us a little bit about how this project came about?

Zach Caldwell (ZC): There was a predicted sea temperature rise this year in the waters around the Maldives. Because we know that corals are more susceptible to bleaching and disease when thermally stressed, this created a timely opportunity to address pressing research questions on the resilience of corals in the Maldives. There seems to be quite a void in quantitative information on coral reefs in the Maldives, so the approach was to organize a comprehensive team to ensure that all necessary information was collected to answer the questions being asked.

RR: What was your role in the expedition?

Photo © Project REGENERATE

ZC: I was a member of the fish team. I worked directly with three other researchers to count and size reef fishes found along our transect line. I also worked directly with Scripps Institution of Oceanography to collect benthic data. We set up 10m x 10m plots on the seafloor and took a sequence of photos of these plots. The photos were later stitched together to make a detailed map of the sea floor. This provides us with a large permanent record of the community structure in that area at that time.  We complimented these data with fish surveys to compare fish abundance with bottom composition.

I conduct similar coral reef and fish surveys in Hawai‘i to provide our community partners with information on the health of their reefs to help inform community-based management. The Nature Conservancy Hawai‘i is currently working with 19 community partners across the State. As a research team, it’s important that we stay up-to-date on the latest monitoring protocols and also contribute to collaborative research projects like Project REGENERATE.

Amir Schmidt (AS): I had three roles to play during the expedition. My first duty was to make sure that the research team was sampling the right places at the right times. With dozens of divers and three dives per day, we had to stick to a tight time schedule! My second role was to oversee the citizen science component of the expedition. This included four local citizen scientists – two people from an environmental NGO, an assessor for Green Fins Maldives, and a representative from the Environmental Protection Agency Maldives – who helped to collect data on fish and benthic life forms, such as corals, sponges, and algae during the whole expedition and eleven community members and resort staff who joined the cruise for a day, receiving on board and in water training on monitoring protocols focused on benthic communities.

RR: How did the idea  to include local community members and scientists in the expedition come about, i.e. what was your motivation for this aspect of the project?

Training

Photo © Project REGENERATE

AS: Our goal for including community members in the expedition was to identify who locally is interested in coral reef monitoring, in order to build a network of citizen scientists to monitor our marine resources and later use this information to create a management plan.

Usually we go to the islands and conduct monitoring workshops there. This time, we took advantage of the opportunity to host the workshops on the research vessel. In addition to the training, the community members got to see what daily life on a research expedition looks like. The Maldivian island communities are small and because transportation in between them is limited, interactions of this kind are extremely rare. I think it was interesting for both the community members and researchers, and helped them to see the bigger picture.

Log on to the Network Forum to read the rest of the interview.

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U.S. Virgin Islands – Disturbance Response


The U.S. Virgin Islands BleachWatch Program

Location
U.S. Virgin Islands

Bleaching Coral. Photo © TNC

Bleaching Coral. Photo © TNC

The Challenge
In 2005, coral reefs throughout the tropical Atlantic and Caribbean were severely impacted by a mass coral bleaching event triggered by prolonged exposure to above normal water temperatures. The bleaching observed in 2005 caused some direct mortality and was also followed by an increased incidence of disease outbreaks. Multiple studies reported this pathway of bleaching followed by increased incidence of disease, with corals varying in degree of mortality resulting from both stresses. This event caused resource managers to realize a formal plan was needed to better respond to coral bleaching events and communicate with stakeholders.

Actions Taken
The U.S. Virgin Islands (USVI) BleachWatch Program was developed to assess and monitor coral bleaching primarily from warm water events and document the distribution, severity and impacts of bleaching to reefs and reef communities. The program was developed by adopting and modifying strategies from the Great Barrier Reef Marine Park and Florida’s successful BleachWatch programs.

BleachWatch BCD Tag

BleachWatch BCD Tag. Photo © TNC

Program Development
To guide the development of bleaching response efforts a steering committee was formed. The committee was composed of reef experts from local and federal government resource agencies, non-profit organizations, and academia. The Bleachwatch Program is one of five main components of the US Virgin Islands Reef Resilience Plan (VIRRP), a larger planning effort to conserve coral reefs in the USVI and promote coral reef resilience.

The VI Reef Resilience Plan and steering committee were necessary to generate and document agreed upon protocols between key stakeholders for the Bleachwatch Program. The Plan provides details on the purpose, response activities and triggers, monitoring protocols and community volunteer training. See further details of the plan below:

Assessment and Monitoring
NOAA’s Coral Reef Watch (CRW) Program, provides current reef environmental conditions to identify areas at risk for coral bleaching, and is used to prepare and respond to mass bleaching events. The following CRW products are monitored by The Nature Conservancy (TNC) in the USVI to provide a early warning system: Alert Areas, Hot Spots (current thermal stress), Degree Heating Week (DHW), Sea Surface Temperature (SST) and Sea Surface Temperature Anomaly (SSTA). These products are available free to researchers and stakeholders to understand and better manage coral bleaching in the region.

USVI Bleachwatch response activities are directly based on advisories and alert levels received from NOAA along with local temperature data. When a Bleachwatch alert is received from CRW by TNC, volunteers are mobilized. They are the first eyes in the water, reporting basic observations such as presence or absence of bleaching. Volunteers are asked to collect data for any areas they visit and also asked to survey specific sites of interest such as coral nursery outplantings and sites assessed with high resilience. If a more severe event takes place, TNC alerts the steering committee and the scientific community. During this time, volunteers might continue to assist with monitoring, but data is more specific and collected at a finer scale to estimate of the percentage of coral reef affected.

Alerts are issued by NOAA only when a station experiences a change in thermal stress level. Table 1 presents a summary of the advisories/alert levels from NOAA monitored by TNC, definitions of the each levels and the response of the USVI Bleachwatch program to each advisory.

BleachWatch Table 1

Community Volunteer Training
Individual volunteers from the public are a main component of the USVI Bleachwatch Program and contribute to the assessment of coral bleaching. BleachWatch assessment methods are taught through in-person training sessions (Since 2013, 4 volunteer trainings have been conducted in St. Croix and St. Thomas). Training sessions are 1 hour in length and focus on the identification of corals reef, fishes, and other creatures. Differences between bleaching, disease and mortality are discussed. Each session also includes training on survey methods, materials, methodology and guidelines for submitting data. A USVI Bleachwatch website was developed to communicate with volunteers and the public. Volunteers have the option of submitting reports through an online datasheet, by email or mail.

USVI Bleachwatch Volunteer Survey Methodology
Conduct a 15 minute roving snorkel or dive pausing each 3 minutes to document a “survey station”. At each survey station:

  • Take a photo or record data for a 1 m2 surface area of the reef
  • Estimate percent coral coverage and percent bleaching of coral
  • Report observations of the absence of bleaching
  • Record other findings such as number and types of herbivorous fishes, number and types of invertebrates and types of diseases
  • Record your findings on the VIRRP BleachWatch Reef Assessment Data Sheet

Materials Needed

  • Diving or snorkeling equipment
  • Underwater clipboard or slate
  • Underwater datasheet and pencils
  • Coral Watch Bleaching Cards
  • Underwater digital camera or video camera – if available (optional)

How Successful Has it Been?
Since the launch of the USVI BleachWatch Program over 35 individuals on St. Croix and St. Thomas have been trained to identify and quantify the severity of bleaching. In 2014 the program protocols were tested for the first time. A Bleachwatch alert was sent out and volunteers were successfully mobilized to survey sites for bleaching. Over 30 reports were received and, fortunately, no bleaching was observed. The secondary response components of the program have been fully tested, as there has not been significant bleaching of corals in the territory since 2005.

The USVI Bleachwatch Program has resulted in increased support and capacity for resource managers to identify and respond to bleaching events. Volunteers are functioning as an early warning system for bleaching events. Managers and the scientific community have a clear plan for assessment and response to bleaching events to inform the proactive management of coral reefs during severe bleaching events.

Lessons Learned and Recommendations
The most important lesson learned is to be mindful that not all volunteers will collect data uniformly. In some instances volunteers are comfortable only sharing whether or not bleaching was observed, which is also important information. It is important to be mindful of volunteers’ time and welcome any level of information that they are willing to share.

Here are some additional recommendations to consider when developing a program:

  • Have a point person in place to keep program organized and lead communication with steering committee members and volunteers. During the development of the program it is critical to determine who can serve as point of contact for the program, this requires staff time for coordination. Consider where point of contact responsibilities can be integrated into existing or complementary efforts for example coral reef monitoring efforts.
  • Clearly defining benefits, incentives, and creating a feedback loop to the volunteers is important.
  • Be flexible and realistic about of the quality of data you hope to receive and the format in which you will receive it from the volunteers – some will fill out the entire form, some will just send an email.
  • Provide other alternatives and options for reporting such as a mapping tool to make it easier for people to report the event.
  • Group volunteer time effort – consider expanding the topics included in a training to include other issues affecting coral reef health that volunteers are interested in reporting for example; invasive species, grounding damages.

Funding Summary
National Oceanic and Atmospheric Administration Coral Reef Conservation Program

Lead Organizations
The Nature Conservancy

Partners
The Nature Conservancy
The University of the Virgin Islands Center for Marine and Environmental Studies

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Micronesia – Predator Outbreaks


A Well-Developed Community-Based Marine Protected Area Proves Resilient to a Crown-of-Thorns Sea Star Outbreak

Location
Nimpal Channel Marine Conservation Area, Yap, Federated States of Micronesia

The Challenge
Yap State is situated in the westernmost region of the Federated States of Micronesia (FSM). The main island of Yap State is located within the Indo-Pacific center of biodiversity. The island is approximately 100 square kilometers, with a densely vegetated and hilly landscape. It is home to 7400 residents spread over 10 municipalities, a relatively small population compared to the other states of Micronesia. The population and urban center are slowly growing, placing increasing pressure on the islands’ natural resources for subsistence and economic gain.

The Nimpal Channel is located off the central-western coast of Yap. Both Okaw and Kaday villages have their fishing grounds associated with the Nimpal Channel. The villages are within the municipality of Weloy, home to approximately 1000 residents. In 2005, a men’s village meeting was called to address the ongoing problem of overfishing in their channel, and decided to seek help and information from outside their community. In 2006, a rapid ecological assessment (REA) was conducted across Yap Proper, including the Nimpal region, so that stakeholders could get a better sense of the current status of their resources. The coral-reef monitoring and assessment team for the REA process consisted of many knowledgeable fishermen from Okaw and Kaday villages, as well as regional scientists with local and global expertise. Following data collection and reporting efforts, and realizing that Nimpal’s resources were not as well off as many other places in Yap due to both natural causes and local fishing pressures, these two villages began discussing their desire to set aside part of their reefs as no-take fishing areas.

Monitoring seagrass beds. © Nimpal Channel MCA.

Monitoring seagrass beds. © Nimpal Channel MCA.

While the Nimpal Channel is very narrow (approximately 0.5 kilometers in width) and has only a limited mangrove stand associated with it, the two communities proposed to make it a Marine Conservation Area (MCA). Through the REA process, marine scientists recommended areas for protection that were larger, deeper, and had more extensive connections with nearshore mangrove habitats known to nourish juvenile fish populations. To marine scientists, the area that Okaw and Kaday proposed to set aside was clearly influential for the locally-owned marine resources, yet was smaller in size and harbored less biological diversity in comparison to other larger and more extensive channel systems nearby. In short, this was not the most ideal area to bolster fishery resources based upon ecological criteria alone. However, the timing was right, and the two communities strongly supported management in that area. Shortly after, in May 2008, Okaw and Kaday, in partnership, publically declared the Nimpal Channel as a Marine Conservation Area with technical support from the Yap Community Action Program.

Within only 1-2 years, monitoring results began to document improved fishery resources in the conservation area. These positive results were an immediate testament to strong community support for management, and dedicated local enforcement. Four years after formalizing the Nimpal Channel Marine Conservation Area, in 2012, a more formal scientific assessment of the channel reefs highlighted that the reef’s condition is second-highest among other MCAs in the region despite having one of the smallest extents. The MCA exceeded the expectations of many marine scientists and changed the way they thought about establishing new marine protected areas going forward. In this case, strong social acceptance and enforcement was more important than ecological criteria.

A crown-of-thorns starfish on a reef in Yap outside of Nimpal MCA. © Peter Houk

A crown-of-thorns starfish on a reef in Yap outside of Nimpal MCA. © Peter Houk

In late spring 2009, Acanthaster planci, commonly known as the crown-of-thorns sea star (COTS), began populating the coral reefs around Micronesia (from Pohnpei westward to Yap). A. planci is a carnivorous species of starfish that preferentially preys upon hard corals such as Acropora spp. and Montipora spp. A. planci were first quantified in monitoring programs off the southwest coast of Yap, and anecdotal reports from fishermen and data suggested a northward migration up the west coast of the island.

Actions Taken
Healthy coral reef systems with high levels of fishery resources have been shown to be resistant to the threat of an A. planci outbreak based upon recent evidence from places like the Great Barrier Reef and Fiji. While the exact mechanism remains elusive, there appears to be some added resistance to these natural disturbance events from healthy fish populations through predation and/or other biological interactions. Reefs that have already been stressed by increased sedimentation, reefs with low numbers of predators due to overfishing, and reefs with low coral diversity have proven most vulnerable to A. planci predation.

Acropora coral showing feeding scars from crown-of-thorns starfish on a reef outside of Nimpal MCA in Yap. © Peter Houk

Acropora coral showing feeding scars from crown-of-thorns starfish on a reef outside of Nimpal MCA in Yap. © Peter Houk

This outbreak of A. planci was not a new threat for Yap. A. planci outbreaks have been described as natural, cyclical events. There are a few theories on why the outbreaks occur. Some experts theorize that COTS outbreaks occur when the sea stars ‘sense’ oceanic conditions are most conducive for their larval offspring to successfully develop, and hence the initial outbreaks may be triggered by some form of nutrient enrichment in the surface waters near coral reefs. Following spawning from initial population outbreaks, it has also been hypothesized that larvae may get caught in ocean currents and somehow influence secondary starfish outbreaks downstream. In Yap, the single most significant COTS event was documented in the early 1970s, although there is local knowledge of smaller outbreaks over the years.

To the local community, the sea stars are well known, but their lifecycles remain mysterious. Locals understand the origins of threats to the reefs like bleaching, sedimentation, and overfishing; however outbreaks of the crown-of-thorns sea stars just suddenly occur without any obvious proximal cause. During the 2009 A. planci outbreak there was no official attempt on Yap to remove the sea stars from their reefs, but fishermen noted their presence. In the case of the Nimpal MCA, the communities did not choose to remove starfish because of adherence to the established no-take MCA policy.

How Successful Has it Been?
The recovery of the coral reefs to the A. planci outbreak in Yap varied. A recent study revisited the study sites where coral populations were monitored as part of the 2006 REA survey and found interesting results. Many reefs along the western coast of Yap showed an expected decline in coral colony sizes and diversity, yet there was one unique exception. The Nimpal Channel MCA appeared to be more resilient to the disturbance event compared with sites to the north and south of this channel. Remarkably, no sea stars were found in the protected area during surveys shortly after the COTS event. In fact, monitoring of the area during the disturbance revealed an increase in coral colony sizes, no significant change in diversity within coral groups, and consistently high fish biomass. Reefs in the protected area showed high abundances of Porites spp. (the less desired coral for A. planci) but Acropora spp. also remained throughout the disturbance period. The area’s resistance to COTS is hypothesized to be due to an intact predator fish population and high coral diversity.

Community participants in a planning workshop. © Nimpal Channel MCA

Community participants in a planning workshop. © Nimpal Channel MCA

In contrast, formerly diverse reefs with extensive coral growth, such as off the southwestern tip of Yap, had the greatest coral reef damage after the sea star outbreak, with little recovery reported as of 2013. Other coral reefs to the north of the Nimpal Channel MCA started to recover in 2012, but recovery has been a slow process and remains ongoing. These findings suggest that the establishment of the locally-managed MCA may have benefitted the resilience of Nimpal’s reefs, and might be supporting recovery along adjacent reefs.

This case study highlights the importance of well-managed marine protected areas for weathering disturbance events. Nimpal Channel MCA appeared to provide added resistance to the COTS disturbance through a series of highly influential, but still poorly understood, ecological processes.

Installing monitoring equipment. © Nimpal Channel MCA

Installing monitoring equipment. © Nimpal Channel MCA

While the Nimpal Channel MCA was initially established to aid fish stock recovery, it was later found to have added benefits of enhanced resistance to COTS. The success of the Nimpal Channel Marine Conservation Area in both enhancing fish populations and mitigating the damage done by the 2009 disturbance continues to be a very popular and productive discussion at regional management meetings across Micronesia. This example shows that marine protected areas have additional benefits that we are only beginning to understand. Certainly the list of benefits will grow into the future.

Lessons Learned and Recommendations
People, rather than biology and science, are most important to think about when establishing a marine protected area. Without the community’s dedication to protecting their channel, the Nimpal Channel Marine Conservation Area would never have been established. Based on biological considerations and the small size of the managed area, scientists felt other areas were better suited to set aside as a protected area; it was only through the community’s will and support that their protected area was established. Science is used to drive management recommendations, but other factors might be more relevant for successful management.

The success of a marine protected area is dependent on community involvement and knowledge. The success of the Nimpal Channel MCA is due to community-based decisions based in traditional ecological knowledge and supported by scientific measures. Consequently, the Nimpal Channel MCA is one of the few functioning protected areas in Yap.

Quantitative monitoring is essential for responding to increased frequency and intensity of disturbances. Identify critical biological thresholds in your management area. Reef ecosystems are complex systems that can behave in a non-linear manner (for instance, the decline of a predator fish population might not have the effect of reducing a reef’s resistance to an A. planci outbreak until the predator fish population declines past a critical threshold). Part of this non-linear behavior is related to trophic interactions (interactions between predators and prey, for example). Science has not fully explained trophic interactions and thresholds in coral reef systems. Disturbances are becoming more and more frequent; there might be a COTS outbreak one year and a bleaching event the next year. Because of the increasing frequency and severity of threats to coral reefs, it is important to collect quantifiable data to be able to perceive rates of change. For example, monitoring fish biomass in your area can be a good starting point to understanding how fish biomass is related to reef resilience. The relative level of biomass within different trophic levels may be related to the maintenance of coral reefs through time.

Funding Summary and Partners

Kaday Community and Cultural Development Organization
Pacific Marine Resources Institute
Yap Community Action Program
Marine Laboratory, University of Guam
Water and Environmental Resource Institute of the Western Pacific, University of Guam
Palau International Coral Reef Center (PICRC)
The Nature Conservancy Micronesia Program
Micronesian Conservation Trust
Seacology
Conservation International’s Pacific Islands Program
Pacific Development & Conservation Trust
OneReef Micronesia

Written by: Peter Houk, Marine Laboratory, University of Guam
Berna Gorong, Kaday Community and Cultural Development Organization
Eva Buthung, Yap Community Action Program, Marine Program

This case study was adapted from: Cullman, G. (ed.) 2014. Resilience Sourcebook: Case studies of social-ecological resilience in island systems. Center for Biodiversity and Conservation, American Museum of Natural History, New York, NY.

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Herbivory And The Resilience Of Caribbean Coral Reefs: Knowledge Gaps And Implications For Management

This paper explores herbivory and how it affects the resilience of coral reefs in the Caribbean. The authors identify important knowledge gaps that limit our ability to predict when herbivores are most likely to support resilience. The authors explore:

  • What processes operate to prevent or facilitate coral persistence and recovery, and how are these influenced by herbivory?
  • What are the independent and combined effects of different species of herbivores in limiting algae and facilitating reef-building corals?
  • What factors limit herbivore populations and the process of herbivory on coral reefs?

The impacts of herbivores on coral reef resilience are likely to be highly context- dependent, thus it is necessary to understand the roles that particular types of herbivores play in limiting harmful algae and facilitating corals under a range of environmental conditions to improve sustainable management of coral reef ecosystems.

The paper provides specific information to guide how to manage herbivore populations to facilitate healthy, resilient coral reefs. The authors present the following management recommendations/guidance:

  • Local management efforts should focus on minimizing direct sources of coral mortality, such as sedimentation and pollution, as well as restoring ecological processes, such as herbivory, that are important for coral persistence and recovery
  • Maintaining healthy herbivore populations is likely to mitigate the negative impacts of ocean warming since abundant herbivores can control algae that inhibit coral recovery following coral decline
  • Better spatial management of fishing could minimize trade-offs between the need to maintain high levels of grazing while supporting sustainable fisheries
  • Implementation of marine protected areas or other spatial restrictions on herbivore fishing will only be effective if we can sustainably manage herbivore populations outside of protected areas. Different species of parrotfishes have different life-history traits and different impacts on benthic communities, thus should not be managed as a single species complex
  • Managers will need to ensure that reefs have the right mix of herbivores to carry out the full set of functions normally performed by the herbivore guild
  • It is critical to protect seagrasses and mangroves, which are important nursery habitats for several species of Caribbean herbivores
  • In cases where degradation has been severe and feedbacks are operating that could slow or prevent coral recovery, management actions targeted specifically at breaking feedbacks that maintain reefs in a degraded state are necessary

Author: Adam, T.C., D.E. Burkepile B.I. Ruttenberg, and M.J. Paddack
Year: 2015
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Marine Ecology Progress Series 520:1-20

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Recovery Potential Of The World’s Coral Reef Fishes

Fishing is the primary source of reduced reef function globally. Marine reserves are a critical tool to help fish populations recover, however, there are no benchmarks to determine if the protection is effective, or whether a reserve has recovered enough to be fished again. By studying remote and marine protected areas, they estimate how many fish would be on a coral reef without fishing, and how long it should take newly protected areas to recover. This helps to assess the impact of reef fisheries, and make informed management decisions that include timeframes for recovery.

Specifically, this paper presents the first empirical estimate of coral reef fisheries recovery potential, compiling data from 832 coral reefs across 64 localities (countries and territories. The authors estimate the expected density of reef fish on unfished reefs; quantify the rate of reef fish biomass recovery in well-enforced marine reserves; characterize the state of reef fish communities within fished and managed areas; predict the time required to recover biomass and ecosystem functions; and explore the potential returns in biomass and function using off-reserve management throughout the broader reefscape. The research team studied the fish biomass on coral reefs around the world and discovered that near-pristine reefs contain 1,000 kg of fish per hectare. Using this figure as a benchmark, they found that 83% of fished reefs have lost more than half of their fish biomass (volume of fish).

The authors discuss how reef fish populations were better off when fishing activities were restricted (e.g., including limitations on the species that could be caught, the gears that could be used, and controlled access rights). The authors determined that once protected, fished reefs take about 35 years to recover, while heavily depleted reefs take almost 60 years. Although the influence of marine reserves can be detected within several years, this global analysis demonstrated that full recovery of reef fish biomass takes decades to achieve. Importantly, this suggests that most marine reserves implemented in the past 10–20 years, will require many more years to achieve their recovery potential. This has important implications for managing expectations of MPAs and also reinforces the need for continued, effective protection and consideration of other viable management options. The authors also found that in reef areas where MPAs cannot be implemented, a range of fisheries can have substantial effects on fish functional groups that support important reef processes.

Author: MacNeil, M.A., N.A.J. Graham, J.E. Cinner, S.K. Wilson, I.D. Williams, J. Maina, S. Newman, A.M. Friedlander, S. Jupiter, N.V.C. Polunin, and T.R. McClanahan
Year: 2015
View Abstract
Email for the full article: resilience@tnc.org

Nature 520: 341-344. doi:10.1038/nature14358

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Biogeography And Change Among Regional Coral Communities Across The Western Indian Ocean

Following the major 1998 coral bleaching event between 2004 and 2011, 291 coral sites from 11 Western Indian Ocean (WIO) countries were surveyed to evaluate regional biogeographic patterns of coral communities along latitudinal gradients and in relation to biogeography and fisheries management. Coral reef abundance, biodiversity, and susceptibility to bleaching were assessed during that period to develop an extensive database on coral reef communities and researchers aimed to evaluate possible impacts such as fishing and fishing closures on reef patterns and status. Patterns show that coral communities are influenced by large-scale interactions between biogeographic factors and temperature abnormalities but not so much by fisheries management. All coral reefs in the WIO are experiencing climate change and coral bleaching since the early 1980s, but at variable rates, timing and scale depending on the geography. The region was characterized by a complexity of a large number of significant interactions among variables tested. The northern Mozambique Channel demonstrated the strongest signs of resilience to climate disturbances.

Author: McClanahan, T.R., M. Atewberhan, E.S. Darling, N.A.J. Graham, and N.A. Muthiga
Year: 2014
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PLoS ONE 9(4): e93385. doi: 10.1371/journal.pone.0093385

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