Invasive Species: Their Threat to MPAs, and How Practitioners Are Responding

MPA News

Owing in large part to increased globalization of shipping, the unintentional transfer of plants and animals from one water body to another worldwide has boomed in recent decades; many bays near major ports are now host to dozens or even hundreds of non-native species. Some of these visitors thrive in their new habitats, outcompeting native species and changing ecosystems, sometimes dramatically. For MPAs, such invasions pose a major threat, particularly when management is unprepared for them.

Nonetheless, due to unfamiliarity with the problem, shortage of funds, or other reasons, there have been few cases worldwide in which MPA practitioners have specifically addressed the threat of invasive species in planning or management. This month, MPA News examines the elements of protection against bioinvasions, as well as cases in which practitioners are working to keep their MPAs safe.

Vector management

MPAs are generally designed either to (a) protect species and habitats that are already on site or (b) encourage re-establishment of those that were there in the past. However, an invasive species that is particularly well-suited to an ecosystem, with no natural predators, parasites, or pathogens to control its population, can change that ecosystem to one never seen before. The invader's population soars while populations of competitors - for food, space, light, or other needs - shrink. A cascade of effects throughout the system may result.

Examples of how invasive species have taken over marine and coastal systems include these:

  • The seaweed Caulerpa taxifolia, originally native to the Pacific and bred in Europe for aquarium use, escaped from an aquarium in Monaco in the mid-1980s. It proceeded to colonize and smother vast areas of the Mediterranean, dispersed by anchors, fishing gear, and other pathways.
  • The comb jelly Mnemiopsis leidyi, transported in ballast water by a ship from the Americas, first appeared in the Black Sea in the 1980s and quickly exploded in population, consuming much of the sea's zooplankton, fish eggs, and fish larvae. Commercial fisheries nearly collapsed.
  • The European green crab (Carcinus maenas) has invaded numerous coastal communities worldwide by a variety of pathways. Green crabs are omnivores, eating mollusks and many other prey items, and have been blamed for the collapse of at least one clam fishery in North America.

One of the primary pathways, or vectors, by which marine alien species are transported is on the hulls or in the ballast tanks of ships, says Jim Carlton, a biologist and invasive species expert with the Maritime Studies Program of Williams College and Mystic Seaport (US). A single ballast tank filled from surrounding waters to stabilize an un-laden ship may contain hundreds of species and millions of individuals, he says. Additional vectors include aquaculture, the aquarium trade, fisheries enhancement, and the use of live bait, among others. (Carlton says the green crab established itself in San Francisco Bay [US] following a shipment there of bait worms packed with crab-laden seaweed.)

"The most important current strategy in marine bioinvasion management is the reduction and prevention of invasions by focusing on the vectors that now transport and release non-native species," says Carlton. Controlling how ships release ballast water, for example, can be critical to reducing the threat of invasions in waters near ballast-water release sites. In this regard, the International Maritime Organization (IMO) in February 2004 adopted the International Convention for the Control and Management of Ships Ballast Water and Sediments, setting standards for improved ballast water management worldwide (http://globallast.imo.org). The convention regulates where, when, and how to release ballast water, and awaits ratification by 30 nations to take effect.

As indicated by the need for such a convention, the problem of marine invasive species is one that transcends MPA boundaries: alien species, if not deposited directly into an MPA, can still float, swim, or crawl there from outside. To work best, vector management programs should be conducted at regional, national, or international levels. Individual MPAs can help by raising awareness among authorities of the problem and its potential impacts on protected areas, and supporting the adoption of vector management approaches in their region.

MPAs can also play an invaluable role in early detection of regional invasions through their normal monitoring programs. "Adding early detection of invasions to MPA monitoring is key," says Carlton. "The early detection and rapid destruction of an incipient population of an exotic species may be second only to preventing the invasion in the first place." He notes that the public can play a major role in early detection programs by alerting authorities to unfamiliar species of animals and plants. Particularly important, he notes, are those stakeholders who have life-long familiarity with the regional biota.

When a potentially invasive species is discovered inside an MPA, rapid response to eradicate it is key. The longer the wait to respond, the more likely it is that the species will establish itself, making full removal difficult if not impossible. This is particularly the case where the original delivery vector remains in place.

Preventing invasions: Northwestern Hawaiian Islands, US

In terms of being able to prevent bioinvasions, the ideal MPA would be one that was remote with relatively little vessel traffic. In addition, its primary visitors would be aware of the threats posed by alien species, and would take voluntary steps to avoid introducing them.

This largely describes the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, or NWHICRER. Despite the site's proportions - at 341,000 km2 in area, it is the world's second largest MPA - the reserve comprises the most remote large-scale coral reef ecosystem on the planet, stretching northwestward from the main Hawaiian Islands in the middle of the Pacific Ocean. It has few human residents and no major ports. And its primary visitors - scientists there to study the region's reef ecosystem - have undertaken several measures aimed at ensuring they do not bring unintended visitors with them.

Despite these protections, invasive species remain a big concern to NWHICRER managers, even compared to other problems such as marine debris, which gets trapped by the islands in enormous quantities. "While the impacts of marine debris to Northwestern Hawaiian Islands ecosystems are significant, invasive and introduced species may ultimately pose a more significant threat," says Randy Kosaki, research coordinator for the reserve. "Whereas accumulations of marine debris can be removed and may ultimately be controlled at their sources, introductions of marine alien species are essentially irreversible. Thus prevention of introductions is among our highest priorities in managing anthropogenic impacts."

In these islands, the main potential vector for alien species is the hulls of vessels, says Kosaki. "Of the relatively few vessels that access the Northwestern Hawaiian Islands, research ships are among the most frequent visitors," he says. "Thus, they are likely candidates to serve as vectors." Most ships operated by the National Oceanographic and Atmospheric Administration (NOAA) are home-ported in the main Hawaiian Islands, at ports with numerous non-native species. Such species could hitch a ride on a ship's hull to the reserve and start up a new colony.

"All NOAA ships accessing the NWHICRER on reserve-sponsored research trips are subject to voluntary hull inspections by trained divers prior to departure," says Kosaki. "This is in part a feasibility study to see whether such regular inspections are practical and cost-effective. If this pilot program is successful, such inspections may be considered as potential regulations for all NOAA ships going to the Northwestern Hawaiian Islands."

In addition, dive gear used in the main Hawaiian Islands by researchers is subjected to a 24-hour freshwater soak prior to use in the NWHICRER, and gear is also given a 10-ppm chlorine freshwater immersion between reefs in the reserve. "Such dips should prevent introductions of alien species via dive gear and minimize the probability of research divers becoming vectors for viral pathogens that may underlie some coral disease syndromes," says Kosaki.

Scientists are even working to prevent unnatural transfer of genetic information between reefs in the reserve. "The Northwestern Hawaiian Islands are one of the few large-scale coral reef systems where meta-population models and rates of gene flow between reefs can be studied," says Kosaki. "Researchers on reserve expeditions must release all organisms at the reefs from which they were collected to avoid artificial facilitation of gene flow." Like the other preventive measures, this is voluntary but may be considered as a regulation or permit requirement for the reserve in the future, he says.

Reserve scientists are working with researchers at other institutions to develop technologies for management needs, including invasive species detection. One project underway with the University of Hawaii, for example, is identifying genetic markers for alien species; with that knowledge, inspectors will be able to detect the presence of unwanted alien species from ship hull swab samples prior to departure for the reserve.

Combating an invasion: Monterey Harbor, US

Eradication of marine invasive species is still a relatively new field; cases of the successful removal of an invasive species are rare, unfortunately. Monterey Bay National Marine Sanctuary (MBNMS), off the US state of California, is working to fight the invasion of a seaweed species that has colonized a harbor neighboring the MPA, and personnel recognize the challenge they face.

The Asian kelp Undaria pinnatifida, more commonly known as wakame, was discovered in Monterey Harbor in August 2001. A highly invasive species that is native to eastern Asia, Undaria has been found in New Zealand, Australia, Argentina, the Mediterranean, and the UK over the past 30 years. At the time of the colony's discovery, Monterey Harbor was already host to dozens of documented alien species, although no concerted eradication attempts had yet been made by authorities. But Undaria - with its rapid growth and high fecundity, among other characteristics - was particularly viewed as a potential threat to the sanctuary's native kelp forests located nearby. With the invasion localized to the harbor at that point, MBNMS moved to address it and, if possible, eradicate it.

First, researchers determined the extent of the colonization. "Initially several individuals were found, but subsequent searches in late 2001 and early 2002 indicated that Undaria was more broadly distributed in the harbor than had originally been thought," says Steve Lonhart, scientist with MBNMS. State and sanctuary officials launched a formal Undaria management program in October 2002. It has involved a team of volunteer divers removing Undaria manually from harbor docks and pilings, with research volunteers collecting data on Undaria locations. So far it appears that the Undaria is keeping pace with the eradication effort. "Given its spread from the center of the harbor to adjacent areas, it is likely that spores are being carried beyond the confines of the harbor," says Lonhart.

He recognizes that eradication of the plant is not possible unless the vector of transmission - vessel hulls in this case - is addressed. "Even if all Undaria were removed from Monterey Harbor, there are no mechanisms in place to prevent reintroduction by vessels entering from infected harbors in Southern California," says Lonhart. "Thus eradication is not a viable option. However, management of the population can reduce the rate of spread to the adjacent open coast and to harbors north of Monterey, and this is currently the main objective." It is unknown how Undaria will interact with the native kelp, which can grow to 150 feet. Invasive Undaria has been observed to grow in thick carpets along the seafloor in New Zealand and Argentina, altering native seaweed communities.

One management option would be to develop a market for the harbor's Undaria, which is commercially grown elsewhere in the world and used in miso soup. Lonhart says a local export company determined that samples of the Monterey Undaria were suitable for human consumption, but that the amount in the harbor was too low so far to be commercially feasible. The concept of harvesting Undaria as food for farmed abalone has also been considered, although it would need to be done in a way to avoid spreading Undaria spores in the process.

Considering the likely vector by which Undaria arrived, would hull-cleaning programs be an option for the sanctuary, including to prevent introduction of additional aliens? Lonhart says that is unlikely. "A program to clean vessels would require a tremendous amount of infrastructure (e.g., a location for inspecting hulls, cleaning them, and managing this information), a significant long-term financial investment, and a program to monitor its success," he says. Unlike NWHICRER, simply too many vessels use Monterey Harbor to make such a program possible, for now. Lonhart hopes that eventually there could be systems to treat vessel hulls with UV light or high-pressure, heated water to kill harmful spores and bacteria quickly and efficiently. In the meantime, MBNMS is monitoring Undaria's spread and its eventual interaction with the native kelp.

Monitoring an invasion: Saldanha, South Africa

West Coast National Park (WCNP) on the Atlantic coast of South Africa contains both an internationally recognized wetland (Langebaan Lagoon) and the country's second largest bulk port, Saldanha. Thanks in part to the heavy ship traffic, WCNP is host to more than half of the marine introduced species observed so far in South Africa. One of these, the above-mentioned European green crab (Carcinus maenas) appears practically tailor-made to take over the park, says Charlie Griffiths, a biologist at the University of Cape Town. "There is concern it may invade the Saldanha Bay system, which contains large areas of ideal habitat," he says.

What Saldanha Bay and WCNP offer the mollusk-eating crab is wave-protected rocky habitat, the availability of which has been the invader's primary limiting factor in its spread up the South African west coast, says Griffiths. Researchers first discovered a mating pair of the crab in Saldanha Bay in 1990.

Griffiths has begun monitoring the crab and other alien species in the park to set a benchmark on their status; future surveys will compare results to see whether spread has occurred. Unexpectedly, his recent benchmark survey of the green crab found just one dead carapace (shell), despite the presence of suitable habitat and numerous potential food species. He suspects the possibility that a population exists at such low densities that no live specimens could be found - which, again, would be surprising considering at least some individuals were present more than a decade before.

There is no eradication program to explain the absence, says Griffiths. "The authorities do not have an eradication program in place pending this or any other invasion," he says. "It is, I guess, an unfortunate reality that in a country in which 20% of the population are HIV-positive, 40% are unemployed, and 50% lack electricity, invasive marine species are not considered a priority issue."

Despite the lack of green crabs in his survey, Griffiths remains concerned about a potential invasion of WCNP - if not by this species then by another. He says the government could take simple steps that would nonetheless help a great deal in fighting invasions in its marine parks: namely, pairing routine surveys by parks authorities with a list of known global invaders known to occur in similar areas elsewhere. This could allow early detection and, potentially, eradication. "The parks authority is the one permanently on site, running tours, inspecting catches, etc., and thus the one most likely to encounter any invasion," he says. "I suggest arming them with the information."

For more information:

James T. Carlton, Williams-Mystic, 75 Greenmanville Road, PO Box 6000, Mystic, CT 06355, USA. Tel: +1 860 572 5359; E-mail: jcarlton [at] williams.edu

Randy Kosaki, Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, 6700 Kalanaianaole Hwy, #215, Honolulu, HI 96825, USA. Tel: +1 808 933 8184; E-mail: Randall.Kosaki [at] noaa.gov

Steve Lonhart, MBNMS, 299 Foam St., Monterey, CA 93940, USA. Tel: +1 831 647 4222; E-mail: Steve.Lonhart [at] noaa.gov

Charlie Griffiths, Zoology Department, University of Cape Town, Rondebosch 7700, South Africa. Tel: +27 21 650 3610; E-mail: clgriff [at] pop.uct.ac.za


BOX: Terminology of bioinvasions

Alien: describes a species that has been introduced to a habitat beyond its natural distribution range; similar terms include non-native, non-indigenous, introduced, and exotic.

Invasive: describes an alien species that acts as "an agent of change and threatens native biological diversity" in its new habitat (IUCN 2000). Not all alien species become invasive. Technically, invasiveness can be difficult to measure, as there are no quantitative guidelines for what constitutes a change or threat to a habitat.


BOX: Advice to managers on invasions - Don Hough, Department of Sustainability and Environment, Victoria, Australia

Don Hough has helped coordinate the Victorian government's efforts on invasive species and its development of a system of marine national parks and marine sanctuaries. MPA News asked him for his advice to MPA managers on invasive species, and he offered these tips:

  • "Keep your boats clean and set an example. Managers are instrumental in promoting prevention of invasions. Prevention is always better than the cure.
  • "Ensure that the work you commission, or the operators you regulate, is done in ways that are sensitive to invasive species risks.
  • "Use your eyes and ears to keep track of new introductions."

For more information:
Don Hough, Department of Sustainability and Environment, 14/8 Nicholson St., East Melbourne Victoria 3000 Australia. Tel: +61 3 9637 8443; E-mail: don.hough [at] dse.vic.gov.au


BOX: Web sources of information on invasions

Invasive Species Specialist Group of the IUCN Species Survival Commission - http://www.invasives.org

IUCN Guidelines for the Prevention of Biodiversity Loss Caused By Alien Invasive Species - http://www.iucn.org/themes/ssc/pubs/policy/invasivesEng.htm

IUCN Aliens newsletter (Number 17 2003), special issue on invasive alien species and protected areas. For a copy, e-mail Carola Warner, University of Auckland, at c.warner [at] auckland.ac.nz

Invasive Alien Species: A Toolkit of Best Prevention and Management Practice, produced by the Global Invasive Species Programme - http://www.cabi-bioscience.ch/wwwgisp/index.html