Local Threats to Coral Reefs

Estimated threat to coral reefs from combined local activities such as development, pollution and fishing

  • Source: WRI/IMaRS USF/IRD/UNEP-WCMC/WorldFish Center

Overview

The health of coral reefs is threatened from many nearby human activities. This Local Threats to Coral Reefs index combines the threat posed by the following nearby activities: overfishing and other destructive fishing practices, watershed and marine-based pollution, and coastal development. This dataset combines these threats into an index of high, medium, or low threat severity at a 1 km resolution.

The dataset was created at the World Resources Institute (WRI) as part of the Reefs at Risk Revisited study and represents threats for the year 2011. The coral reef location dataset used was based on 500 meter resolution gridded data reflecting shallow, tropical coral reefs of the world. Organizations contributing to the data and development of the map include the Institute for Marine Remote Sensing at the University of South Florida (IMaRS USF), Institut de Recherche pour le Développement (IRD), United Nations Environment World Conservation Monitoring Centre (UNEP-WCMC), WorldFish Center, and WRI.

Methodology

Local threats to coral reefs include: coastal development; marine-based pollution and damage; watershed-based pollution; and overfishing and destructive fishing practices. To combine these into one index, the authors defined the factors that contribute to each threat in the following way:

The coastal development threat includes the number, size, population density, and population growth rates of human settlements on the coast; locations of seaports, airports and hotels; and traffic from tourism.

The marine-based pollution and damage threat includes datasets on distance from commercial and cruise ports, shipping intensity as measured by a voluntary reporting scheme, and presence of oil infrastructure.

The watershed-based pollution threat to coral reefs includes sediment deposits accumulated throughout watersheds and released at river mouths. The Revised Universal Soil Loss Equation (RUSLE) is used to calculate the relative erosion potential (REP) for all land areas. The REP levels in a watershed are used to determine how much sediment gets loaded into the water courses of the watershed. Factors such as mangroves and dams reduce the total sediment delivery at the river mouth. A model is used to disperse the accumulated sediment amount in the surrounding ocean area. Thresholds are established to differentiate between ocean grid cells at low, medium, or high threat from sediment deposits.

Severity of overfishing was estimated based on proxies for demand for fish products---coastal population density, extent of official fishing areas, and reef and shallow shelf areas---with special adjustments made to account for increased demand when in proximity to large populations and market centers. Areas where destructive fishing practices occur, such as using explosives or poisons, were included based on observations from monitoring and mapping exercises undertaken by field experts.

The overfishing and destructive fishing threat level may be reduced by one level if a grid cell was inside a marine protected area that had been rated as having “effective” or “partially effective” management. These ratings were sourced from regional experts, who were asked to rate marine protected areas on a three-point scale for management effectiveness.

Depending on the size of these threat factors, distance thresholds are established for whether that threat factor puts a nearby ocean grid cell at low, medium, or high risk of damage to coral reefs. For the full documentation, please see the source methodology.

Data shown on Resource Watch Map

  • Integrated Local Threat Level of Reefs: Estimated threat to coral reefs from combined local activities. Local threats include: coastal development; marine-based pollution and damage; watershed-based pollution; overfishing and destructive fishing practices.

Additional data for global threats to coral are available from the data provider. Please click on the “Download from source” button to find these data available on the source website.

Disclaimer

Excerpts of this description page were taken from the source metadata. Resource Watch shows only a subset of the dataset. For access to the full dataset and additional information, click on the “Learn more” button.

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Formal name

Reefs at Risk Revisited: Local Threats

Cautions

Certain assumptions or simplifications were made about each of the four types of threats considered in this study. The assumptions, listed by category, are described below:

Coastal development:

• Some tourist locations were missed in the modeling process, especially new locations.

• The model did not directly capture sewage discharge, but relied on population as a proxy.

Watershed-based pollution:

• The model used a proxy for sediment, nutrient, and pollutant delivery.

• Nutrient delivery to coastal waters might have been underestimated due to a lack of spatial data on crop cultivation and fertilizer application. However, agricultural land was treated as a separate category of land cover, weighted for a higher influence.

• The model did not incorporate nutrient and pollutant inputs from industry or from intensive livestock farming, which could be considerable.

• Sediment plumes accumulated through inland watersheds and discharged at river mouths can drive reef degradation. After reaching the river mouth, sediment matter disperses according to currents, but the movements of currents were not taken into account in modeling the plume dispersal process. The model designers decided for the sake of simplicity to model the dispersion process as depositing an equal proportion of the plume in successive concentric circles around the river mouth until all of the plume matter has been allocated. This data did not include threats from nutrient deposits released at river mouths, which can cause algal blooms which damage coral reefs.

Marine-based pollution and damage:

• Threats associated with shipping intensity may have been underestimated because the data source was based on voluntary ship tracking, and did not include fishing vessels.

• The threat model did not account for marine debris (such as plastics), discarded fishing gear, recreational vessels, or shipwrecks, due to a lack of global spatial data on these threats.

• The drivers of coral reef degradation include discharged oil, bilge, and ballast liquids from ships involved in world trade. There were no available datasets that measure these discharges, so port and ship traffic density were used as a proxy.

Overfishing and destructive fishing:

• Accurate, spatially referenced global data on fishing methods, catches, and the number of fishers was not available; therefore, population pressure was used as a proxy for overfishing.

• This model didn’t capture the targeting of high-value species, which affects most reefs globally but has fewer ecosystem impacts than wider-scale overfishing.

• Management effectiveness scores were only available for about 83% of the reefs within marine protected areas.

Suggested citation

World Resources Institute. 2011. Reefs at Risk Revisited. Accessed through Resource Watch, (date). www.resourcewatch.org.

Sources

World Resources Institute (WRI)
Institute for Marine Remote Sensing at the University of South Florida (IMaRS USF)
Institut de Recherche pour le Développement (IRD)
United Nations Environment World Conservation Monitoring Centre (UNEP-WCMC)
WorldFish Center

Geographic coverage

Global

Spatial resolution

1 km

Date of content

2011

Published language

en

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