Managing Risks from Invasive Species

Herbivorous sea urchins mature within supervised saltwater tanks to aid in coral patch algae removal. Photo © Ian Shive
macroalgae covers reef in oahu

Invasive macroalgae Graciliaria salicornia overgrowing and smothering coral colonies on O‘ahu, Hawai‘i. Photo © S. Kilarski

A range of invasive species are known to pose risks to coral reefs, including some algae, fish, and invertebrates. Invasive species are organisms that spread rapidly to dominate ecosystems and are likely to cause economic and/or environmental harm. Many invasive species are introduced species that may increase the likelihood of new diseases and decrease the food and space for native species. However, invasives don’t have to come from elsewhere; a native species can become invasive if its natural controls are removed.

Invasive species can cause severe and lasting damage to the habitats they invade by reducing the abundance of native species as well as altering ecosystem structure and processes. In addition to such environmental impacts, invasive species can also result in economic losses to local communities and industries. There are four main approaches involved in managing invasive species:

Prevention is the first and best line of defense in the management of invasive species. To prevent the introduction of invasive species, it is important to understand how invasive species are transported, and therefore introduced. Common pathways of introduction include:

  • Ballast water
  • Biofouling of ship hulls
  • Release of unwanted pets and fishing bait
  • Release or escape of classroom and laboratory animals
  • Transportation on recreational boats and equipment
  • Escape from aquaculture facilities, nurseries, or water gardens
  • Intentionally stocked as food or recreational sources
  • Release as biological control

At a regional or country-level, policies and codes of practice should be in place to reduce the risk of introductions through the most common pathways of introduction. Coral reef managers can work with agencies involved in regulating vessel movements, controlling ports or high-risk activities to evaluate the likelihood and consequence of invasion in coral reef ecosystems, and propose additional controls on species or activities that represent high risk. In recognizing that ship movements are a major source of species invasions, there are a number of standards and best-practice approaches that can be used to reduce risks to coral reefs. For example,  opens in a new windowMarine Biofouling and Invasive Species: Guidelines for Prevention and Managementopens PDF file includes best management practices for ensuring anti-fouling measures are applied to vessels, border control measures of risk assessment, in-water cleaning programs, facilities, and disposal measures.

It is essential to conduct ecosystem monitoring in a timely and systematic manner in order to detect introductions early enough that a rapid response is feasible. Often the only way to successfully eradicate an invasive species is to act very early in the invasion process before an infestation becomes widespread. Effective early detection and rapid response depend upon the timely ability to ascertain:

  1. What is the species of concern, and has it been authoritatively identified?
  2. Where is it located and is it likely to spread?
  3. What harm may the species cause?
  4. What actions (if any) should be taken?
  5. Who has the needed authorities and resources?
  6. How will efforts be funded?

Early detection efforts require resources, planning, and coordination. Invasive species are often detected by chance, but trained individuals and personnel can also detect them through targeted invasive species surveys and by monitoring specific, high-risk areas. Community monitoring networks also can provide important information about changes in reef condition. For example, Hawaii’s  opens in a new windowEyes of the Reef Network engages communities in the monitoring and reporting of marine invasive species, and other reef stressors such as coral bleaching, disease, and predator outbreaks. This network is comprised of regular reef users (recreational users, tourism professionals, researchers, and fishers) who voluntarily monitor and report on reef conditions. An incident response program can guide a systematic effort to eradicate or contain invasive species while infestations are still localized. It is critical to quickly mobilize resources to intensively control an infestation before it becomes more widely established. The ability to share resources across jurisdictions, form strategic partnerships, and have access to plans, funds and technical resources are critical components of an Incident Response Plan. These arrangements can often be put in place before an introduction ever occurs, greatly facilitating a rapid and effective response.

Once established, invasive species can be very difficult to eradicate, especially in highly connected systems such as coral reefs. However, the ecological impacts of an invasive species may justify efforts to control further spread and manage established populations to minimize damage or allow native species to recover. In general, a strategic plan is used to control chronic invasions.

Understanding the ecological, economic, and social impacts of invasive species is important in prioritizing control and management operations. Having a variety of control and management tools gives managers the best chance to assess, contain, and remove invasive species populations and guide management decisions. These tools are applied within coordinated and integrated invasive species management strategies that are adjusted as needed.

Example of Invasive Species Control Programs

Lionfish control programs — Lionfish are an invasive species in the Atlantic, Gulf of Mexico, and Caribbean Sea. They have quickly become established, spreading from their original point of introduction in the Florida Keys. Throughout the region, programs have been established in an attempt to control populations of this highly effective predator. One example is in the Florida Keys National Marine Sanctuary, which now issues  opens in a new windowspecial lionfish removal permits for collection of lionfish from Sanctuary Preservation Areas (SPAs), which are otherwise no-fishing, no-take zones. In other parts of the Caribbean, such as the Cayman Islands, programs have focused on encouraging local fishers to catch and encourage a market for lionfish through education campaigns, including brochures explaining how to safely handle and prepare lionfish.

Restoring ecosystems may be necessary if it has not been possible to prevent ecological damage by an invasive species. Restoration is a labor-intensive and expensive exercise, so should not be contemplated unless the threat from invasive species has been reduced to insignificant levels. Although there are few examples of successful restoration following removal of an invasive species, there are a range of restoration methods available for assisting recovery of coral reefs after damage. Many of these have been developed for use after acute events, such as vessel groundings. Comprehensive guidance is available on reef restoration that will be useful to coral reef managers considering restoration options.

Example of Invasive Species Control Programs

Invasive seaweed removal projects — One example of an attempt at ecosystem restoration is the  opens in a new windowMaunalua Bay Reef Restoration Project which resulted in the removal of over 3 million pounds of Avrainvillea amadelpha (leather mudweed), an invasive alien alga from coral reef habitat in Maunalua Bay, located in southeast O‘ahu, Hawai‘i. Community volunteers alone removed 91,500 pounds of algae. All invasive alien algae were turned to productive use as a fertilizer on local farms. A Community Monitoring Protocol was established in partnership with The Nature Conservancy scientists to monitor the 27 acres that have been cleared. This project is the first critical step to restoring coral reef and seagrass systems in Maunalua Bay.

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