Prevention of Introduction of the European Green Crab Carcinus maenas to the Marine Environments of Hawaii: Methods to Avoid Marine Invasions

Table of Contents

I. Introduction

II. Ecological and Economic Impacts

III. Management Techniques

IV Literature Cited

Introduction

Alien Invasions in the Marine Environment

Around the world a deluge of perhaps irreversible global aquatic invasions is now occurring. While most people are aware of aquatic chemical and nutrient pollution, and sedimentation of our coastlines and waterways, few may be aware of the impact of aquatic alien species. Introduced species can cause irreversible, fundamental alterations in the structure of aquatic ecosystems. No introduced marine organism, once established, has ever been successfully removed or contained.

Historically, marine invasions are not new. With trade routes established in the sixteenth century, aquatic systems may have been contaminated for four or more centuries, leading us to interpret some distribution as natural. These slow moving vessels were at times carrying seaweeds, mussel, barnacles, worms etc. up to a meter thick on their hulls. Today the faster moving ships, also with anti-fouling paint on their hulls, carry hundreds of thousands to millions of gallons of ballast water that can transport vast quantities of marine life.

In the marine environment, any mechanism that can rapidly transport organisms from shallow coastal waters across natural oceanic barriers has the potential to facilitate invasions by entire groups of marine organisms. International shipping, through transport in ballast water or on ship's hulls, provides such a mechanism. Ballast water is used to stabilize empty ships and is taken on board in overseas ports then released at the destination when cargo is loaded. Even though the ballast tanks can be relatively hostile environments, many organisms survive the journey. These organisms include the pathogenic cholera bacterium, Vibrio cholera; toxic dinoflagellate algae such as Gymnodinium catenatum; kelp; larval zooplankton and many other micro-organisms including fish parasites. Some of these organisms can stay alive in ballast tanks for more than 90 days without food or light.

Hawaii is particularly vulnerable to pest introductions via shipping because of its reliance on international shipping for trade, the high volume of dry bulk exports, and the wide geo-graphic spread of its receiving ports. Transit time for vessels between Hawaiian and Japanese ports, for example, is usually less than 20 days, which is shorter than the larval life for a wide range of fish and invertebrate species. Currently, there are no specific identified threats to Hawaii port areas but the extent of the state's port activity, and the economic and esthetic value of its coastal waters are cause for concern. Some coastal water environments create conditions where alien species may flourish. Further, there are a number of noxious predators in other parts of the world which could seriously threaten coral reefs, estuaries and Hawaii's aquaculture

It is suggested that most introduced species do not survive or have very little impact once established in their host environment, and that only a minority of species cause widespread environmental and economic damage. However, natural controls through predation, parasitism and competition which constrain alien species numbers in their natural environment may not be present in Hawaiian waters. This can allow these invasive organisms to multiply and out-compete native species. Unregulated transport of organisms by international shipping has been likened to 'ecological roulette': on most occasions the impacts are slight but at times, may result in costly environmental "train wrecks".

Marine environment of islands is not as "unbalanced" as the terrestrial environment, i.e. terrestrial environment of islands lacks many major vertebrate and invertebrate groups. Marine environment is more "balanced" and the impact of invasive marine species are not usually as devastating. That is not to say there have not been a lot of successful marine introductions in Hawaii such as: Taape, Graciliaria saliconis, Kapophycus, snappers, and Tilapia (Stimson, pers. comm.). For an example the alien species of algae Acanthapora, introduced into Pearl Harbor waters, has quickly spread through the state, displacing native algaes. Research has shown habitat destruction is the most important factor in species loss, and native organisms are vulnerable to habitat destruction and displacement by the invasion of alien species. The uncommonly adaptable European green crab, Carcinus maenas, is one of these species that upon introduction can displace native species.

The European Green Crab

Common name: green crab or common shore crab

Lineage: Eukaryotae; eukaryote crown group; Fungi/Metazoa group; Metazoa; Eumetazoa; Bilateria; Coelomata; Protostomia; Arthropoda; Crustacea; Malacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Brachyrhyncha; Portunoidea; Portunidae; Carcinus

Occurrence - so far: Sweden, Denmark, Scotland, Portugal, Spain, France and England, the North American Atlantic and Pacific Coasts.

Carcinus maenas (C. meaenas or green crab) has the ability to migrate by surface currents, rafting, and invasion (Cals 1983). Differences in habitat usage and size have been seen upon some invasions, whereas the green crab did not colonize protected and exposed rocky shores used elsewhere and have grown much larger than at other sites (Grosholz, 1996). The sites where they grew much larger were those with higher water temperatures.

The green crab is able to breed and spread rapidly, quickly reach adult size, optimize feeding habits, and has an unusually wide tolerance for variation in both water temperature and salinity, making it a threat to Hawaiian waters (Grosholz, 1996). A female green crab can produce up to 200,000 eggs per year, and its planktonic larvae, in theory, can travel up to 400 miles in one generation on Pacific Ocean currents. On the central coast of Maine, it is reported that C. maenas matures when 2-3 years old, breeds 2-3 times, with a generation time of a minimum of 3 years (Berrill, 1982). C. maenas exhibits a range of adult color forms, from green to red.

While snails are one of the favorite diet items of the green crab, the green crab can be insatiable, eating barnacles, clams, oysters, mussels, worms, urchins, crabs, lobster larvae, some plants and small fish. In lean times the green crab will feed on 104 biological families, 18 genera, five plant and 14 animal phyla (if it's alive, it's lunch) (Barshaw et al. 1982).

The green crab is so adaptable that it has been highly recommended as an excellent subject for school study, both in the field and the laboratory.

Ecological and Economic Impacts

West Coast of the North Pacific

Monitoring programs have followed the spread of the green crab along the California coast. It has invaded the North Pacific Ocean following more than two centuries of global dispersal due to human activities. C. maenas was first collected in San Francisco Bay, California, in 1989-1990, where its distribution and prey selectivity were investigated in 1992-1994 (Cohen et al., 1995). It has become abundant in shallow, warm lagoons (which may have served as nurseries) and spread throughout the bay. It may have arrived in ballast water, on fouled ships, amongst algae with imported live bait or lobsters, or by intentional release. The green crab's nature, high breeding potential, and its diet and feeding behavior give it potential for extensive ecosystem changes through predator-prey interactions, competition, disturbance, and indirect effects.

Studies documenting the effect of the green crab in the San Francisco Bay area show dramatic declines in several taxa (Grosholz et al., 1995 ). Based on long-term sampling of this species over the last ten years, the shore crab Hemigrapsis oregonensis showed dramatic declines during the last two years. Also, based on harbor-wide sampling, two small clam species in the genus Transennella have shown very dramatic declines during the last one to two years. Long term counts on the wintering shorebird population in the area appeared to have not declined in response to the green crab. But effects on shorebird abundances may either be delayed behind the impacts on invertebrates or are too slight to be distinguished from other factors. Although reduction or disruption of fisheries has been documented in a few regions, the potential economic impacts in San Francisco Bay remain largely unknown.

Threats to Hawaii

Successful aliens have the ability to spoil native habitat, threaten native plant and animal species' diversity and abundance, and disrupt human social and economic activities dependent on aquatic resources. These impacts are more likely to occur in areas where the alien species does not have natural predators or competition, or in areas where there are few native species to compete with or resist its invasion.

All bays, estuaries, anchialine pools, tidal pools, and areas of reef flats may be habitat for the green crab although it may not become abundant on wave-exposed portions of the coast. As an example, the seaward-facing side of a fringing reef (e.g. West Maui) is exposed to high wave action. In this situation the green crab would more than likely not establish itself. In contrast, wave action on reef flats (e.g. Black Point, O'ahu and large areas of coastal Kauai) is quite low. Green crabs here would be much more likely to become established, particularly in tide pools.

Hawaii is estimated to have 55,000 acres of wetlands, with most less than 5 acres in size (Hawaii Office of State Planning 1992). Wetlands are critical habitats for endangered Hawaiian waterfowl, resident and migratory waterbirds, native plants and aquatic fauna. These sites are also an important site for scientific research and recreation. With the ability to change this type of ecosystem through the disruption of bottom sediments, the green crab would not be a welcome addition.

Anchialine pools, unique to Hawaii, have distinct biotic communities dominated by endemic mollusks and shrimp. These pools are highly susceptible to the introduction of invasive species (Maragos 1975) and may be devastated by an animal as adaptable as the green crab, which can traverse over the shore and into these special areas. Other areas that demonstrate the type of environment favorable to the green crab, and also particularly rich and vulnerable species diversity on O'ahu include: Maili Beach Park (Waianae), Oneula Beach Park to Barber's Point, Chun's Reef (Haleiwa), to Pupukea Beach Park, Malaekahana (Laie), Sandy Beach tide pools (Makapuu Point), and possibly Hanauma Bay.

Because of its size, fast growth, and tolerance to salinity and temperature fluctuations, the green crab can pose a problem to aquaculture, commercial and subsistence lobstering, and to endemic species and their habitats. As the green crab prefers mollusks, endemic marine snails may experience lowered populations and be subjected to related problems. It may also disturb the ecosystem through its burrowing habits in soft sediments.

Although the green crab may just become just another predatory crab species within the marine ecosystem, in some local cases the problems may be severe. However, it's also true that other marine species can adapt and survive. The green crab, if introduced and becomes established, may be become prey for species already present here in Hawaii. Especially when young, it may be eaten by other native crabs, fish, the great night heron, ducks, shore birds, maybe humans. It might make decent fish bait, and in theory it can be eaten - the green crab is harvested and eaten by people in Portugal, Spain, France and England.

If the green crab should form dense enough populations, we could expect some reduction in shellfish, including opihi, wana and lobster, an evolutionary "natural selection" for shellfish with thicker shells, and a displacement of native species, such as the native xanthid crab, from some of their habitats.

Another hypothetical impact could be bestowed upon the tourist industry. As these crabs grow quite larger in temperate waters, and prefer bay areas, where tourists like to swim, their presence may not be appreciated on the shores.

Management Techniques

The philosophy for ballast water management is basically quarantine: ballast management should seek to prevent the introduction of all organisms. This can be accomplished best by using a variety of procedures as no one procedure can guarantee 100% effectiveness. As invasion by marine organisms is a concern of itself and not just limited to the green crab, this section of the paper will address management techniques of larger scope.

According to Sea Grant's Shipping Study (1995), following the invasion of Australia by Japanese dinoflagellates and Canada by zebra mussels, both countries initiated extensive ballast water studies and began exploring regulatory measures. The Hawaii State Department of Land and Natural Resources is currently undergoing this same type of study for Hawaiian waters. By March 1989, Canada instituted voluntary measures requesting that vessels from foreign ports exchange their ballast water in the open ocean. Following the passage of the Nonindigenous Aquatic Nuisance Prevention and Control Act in November 1990, the United States joined Canada in March 1991 to issue joint voluntary guidelines.

In 1990, Australia issued voluntary exchange guidelines as well. In 1991, Australia and Canada, joined by other nations, took their concerns about ballast water as a vector for transporting harmful alien organisms before the Marine Environmental Protection Committee (MEPC) of the United Nations International Maritime Organization (IMO).

In July 1991 the IMO issued voluntary "International Guidelines for Preventing the Introduction of Unwanted Aquatic Organisms and Pathogens for Ships' Ballast Water and Sediment Discharges." IMO member states are requested to follow these guidelines, which also call for open-ocean exchange. A review conducted by Australia in 1993 revealed that few countries had implemented the guidelines. In 1994, a ballast awareness working group of the IMO/MEPC drafted more flexible guidelines in order to encourage greater compliance. Consideration is being given to the adoption of ballast water management protocols as a formal annex to the International Convention on Marine Pollution (MARPOL). If adopted, the annex would require all 130 member nations of IMO to follow ballast management guidelines, which would include open ocean exchange of ballast water when possible.

Near shore and port environments where ships take on ballast water support a higher diversity and number of species than open ocean. Most open ocean species are unique to high seas and generally do not and cannot live in the near shore environment. Exchanging near shore ballast in mid-ocean replaces the diverse, abundant, and highly adaptable organisms with fewer and less diverse open ocean organisms. The risk of discharging this exchanged ballast water into coastal and inland water is considered acceptable. The IMO has determined that ballast exchange is the most efficient method right now to control the spread of indigenous organisms.

Prevention by ballast exchange could be termed as a form of Voyage Approach. Voyage approaches include:

1) Prevention or minimization of the intake of organisms during loading of ballast water: Shore facility provides appropriate water for ballast (fresh, treated, municipal); Organism intake is prevented by avoidance of large sediment loads, areas of sewer discharge, filtration, or by extermination of organisms upon ballasting, i.e. mechanical agitation, altering water salinity, ultraviolet or ultrasound treatments.

2) Removal of organisms prior to discharge of ballast water and sediment (as described above) and also by: Disinfection by biocides, ozonation, thermal treatment, electrical treatment, oxygen deprivation, and the methods in #1 above.

3) Ballast treatment on arrival: Discharge to sewage treatment facilities (preferably tertiary treatment), reception vessel, sediment removal and onshore disposal, non-discharge of ballast water.

4) On-shore treatment of ballast water and settlement.

There currently are experiments into the use of disinfectant processes such as ozone, ultraviolet light and filtration to remove invasive organisms from ballast water. The treatment process must comply with ballast water treatment guidelines set by the International Maritime Organization (IMO) which directs that any treatment must be safe, practical, cost effective and environmentally acceptable.

Ozone gas, a strong oxidant consisting of three oxygen atoms, is used as a disinfectant in marine hatcheries and aquaria. It is known to be effective for the control of many bacteria and viruses. The ozone works by oxidizing the cell walls or damaging the internal functions of organisms. Also widely used for marine water disinfection is ultraviolet light (UV). UV "sunburns organisms to death" damaging the DNA and preventing reproduction.

Filtration acts as a physical barrier to remove organisms. Wedge wire screens will remove larger zooplankton while more complex systems will tackle the smaller phytoplankton.

Other methods to reduce or eliminate alien marine invasions include;

1) Minimizing need; Optimizing cargo types, and loading practices to maximize cargo load and to minimize or eliminate need for ballast.

2) Certification of "Nonindigenous Species-Free Status:" Certification could take several forms including certifying that; the ballast site was free of a given species, water and sediments actually ballasted were free of a given species, site was not at or within a given distance of a sewage outfall, site was not the location for a current human disease outbreak, site was not a place of active dredging.

Some areas have been identified as "Global Hot Spots." These hot spots contain easily introduced and harmful species, such as the Mediterranean Sea containing Caulerpa taxifolia, which is seriously degrading native habitat in this area.

Economics of Ballast Water Management

Previous work in Canada, Australia, and the United States have given some insight to the cost of ballast water management (Sea Grant, 1995). While there are many variables involved, as in vessel size, ballast size, costs for shore services etc., it is estimated that the overall costs would be in the order of $1000s to $100,000s per vessel.

It is more critical to understand the nature and range of the variables (Sea Grant, 1995), these include:

1. Vessel type
2. Vessel size vs. ballast water capacity vs. refit costs
3. Vessel age vs. refit practicability
4. Vessel speed
5. Diversity and variability of ballast tanks
6. Diversity and variability of ballast pump capacity
8. Ballast pump age and efficiency
9. Costs of shipyard service in domestic vs. foreign shipyards
10. Costs of crew training for ballast management
11. Costs of electricity for ballast pumps
12. Cost of crew time, crew fatigue, and/or additional crew, relative to frequency of need to employ ballast management.
13. Administrative and record keeping costs aboard vessel.
14. Administrative and record keeping costs in shoreside company offices
15. Inspection, monitoring, and administrative costs to government monitoring agencies
16. Initial equipment costs
17. Maintenance costs for ballast control equipment
18. Equipment lifetime
19. Changing costs of technology with costs to be determined based upon projected dollar values five years from the study date
20. Costs of delays in port arrivals and departures and delays in cargo handling
21. The transitional costs of the above to the increased costs of shipping overall and thus the passed-on increased costs of raw materials.

The Public

As of yet, there is not knowledge that green crab has arrived, will arrive or when. There are procedures that the general public can use to prevent the spread of alien marine species already introduced to Hawaii's coastal waters.

Just as resource users on land have learn methods to prevent spread of alien species on land, such as cleaning their boots before and after hiking, ocean users can also help stop the spread of marine alien species.

1) Boats, trailers, and boating equipment (anchors, centerboards, axles) should be inspected and any visible plants and animals removed before leaving any water body.

2) Drain water from the motor, livewell, bilge and transom wells before leaving any water body.

3) Empty bait buckets on land before leaving any water body. Never release live bait into a water body or release aquatic animals from water body into another.

4) Wash/dry boats, tackle, trailers and other boating equipment to kill harmful species that are not visible at the boat ramp. Some aquatic species can survive more than two weeks out of water, so it is important to use hot (104 F) tap water or spray with high pressure. Another method is to let boats and boating equipment dry for at least 5 days before transporting to another water body.

Literature Cited

Barshaw, D; Able, K; Heck, K. 1982. Salt Marsh Peat Reefs as Protection for Postlarval Lobsters Homarus americanus From Fish and Crab Predators: Comparisons with Other Substrates. Mar. Ecol. Prog. Ser. vol. 106(1-2) pp. 203-206

Berrill, M. 1982. The Life Cycle of the Green Crab Carcinus Maenas at the Northern End of its Range. J. Crust. Biol. 1982. vol. 2(1) pp. 31-39

Cals, P. 1983. Diverse Migratory Capacities of Crustacean Larvae and Historical Evolution of the Oceans. Life-cycles-and-biogeography. Cycles-de-vie-et-biogeographie.- Bhaud,-m. ed. Paris France Inst. Oceanographique, vol. 9(4) pp. 355-387

Cohen, AN; Carlton, JT; Fountain, MC. 1995. Introduction, dispersal and potential impacts of the green crab Carcinus maenas in San Francisco Bay, California. Marine Biology, vol. 122(2) pp. 225-237

Grosholz, E; Hedgecock, D; Ruiz G. 1995. Impact of the Recently Introduced Green Crab on Invertebrate and Shorebird Populations. Marine Biology, vol. 126(1) pp. 56-61.

Grosholz, ED; Ruiz, GM. 1996. Predicting the Impact of Introduced Marine Species: Lessons from the Multiple Invasions of the European Green Crab Carcinus maenas. Biol. Conserv., vol. 78, no. 1-2, pp. 59-66.

Office of State Planning. 1992. Hawaii Coastal Zone Management Program, Section 309 Coastal Zone Enhancements Grants Assessment. Office of State Planning. Office of the Governor, State of Hawaii.

Maragos, JE; Smith, S; Kay, A; Kam, D; Maciolek, J. 1975. Hawaii Coastal Water Ecosystems: An Element Paper for the Hawaii Coastal Zone Management Study. Technical Supplement No. 14, Hawaii Coastal Zone Management Program.

Norse, EA (ed). 1993. "Global Marine Biological Diversity: A Strategy for Building Conservation Into Decision Making" Island Press, Washington DC 1993.

Sea Grant Conneticut. 1995. Shipping Study; the Role of Shipping in the Introduction of Nonindigenous Aquatic Organisms to the Coastal Waters of the United States (Other Then the Great Lakes) and an Analysis of Control Options. Prepared for the United States Coast Guard and U.S. Department of Transportation. The National Sea Grant Program, Conneticut Sea Grant Project R/ES-6

Written By: Victoria Cullins

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