4.2 OVERVIEW OF THE PROBLEM OF EXOTIC MARINE ORGANISMS
4.2.1 Transfer by shipping of exotic marine organisms
It has been shown that large numbers of species can be transported by ballast water and on the hulls of ships. An American study found over 400 species of plankton and bottom living organisms in the ballast tanks of Japanese ships over a period of four years91 Over twelve marine and brackish water phyla have been identified in ballast water. The most frequently occurring are nematodes (round-worms), rotifers, polychaetes (bristle-worms) and crustaceans. Other commonly occurring organisms are ciliates (protozoans), fish, and larvae of mussels and snails92 A study of foreign ballast water in more than 70 vessels arriving at Chesapeake Bay (United States) found that at least 90 percent of the vessels carried live organisms. In addition, schools of juvenile fish were found in the ballast tanks of ships entering Chesapeake Bay from the United Kingdom, the Netherlands and Israel93 The hulls of ships are also important vectors for the transfer of a wide variety of exotic marine organisms. (Chapter 3).
4.2.2 Ecological impacts of exotic marine species
Introduced species have the potential to seriously disrupt ecosystem relationships and environmental processes, threatening native species and the integrity of the natural environment, human health, aquaculture sites, tourism and enjoyment of coastal amenity94 It is recognised that once introduced and widely established in an open aquatic system, exotic species are extremely difficult to eliminate95
4.2.2.1 Reduction of biodiversity
Reduction of biodiversity as a result of exotic marine species introductions is an issue of growing concern96 As indigenous species decline in response to aggressive invading species, populations become increasingly homogenous. The loss or reduction of native species' populations may occur due to predation by exotic species; competition for food and habitat; and through the introduction of new diseases97
4.2.2.2 Genetic changes to populations
Within a species, populations from separate locations may be genetically different to each other. The movement of individuals of a species (exotic or indigenous) between ports via ballast water or on the hulls of ships, may result in a change in the genetic structure of the destination population. This may change the sensitivity of a population to disease, or affect the population's ability to adapt to future environments98
4.2.2.3 Physical effects on the environment
Introduced organisms may alter the physical environment, changing the physical properties of substrata, the sediment chemistry or affecting light penetration. These changes in turn may inhibit or enhance the survival and reproduction of other species in the community.
4.2.2.4 Eutrophication
One of the most serious threats to aquatic ecosystems throughout the world is nutrient enrichment.99 High nutrient levels may arise due to inputs such as sewage or agricultural fertiliser run-off. In some cases, exotic species may disturb the ecological processes that help to maintain the balance of nutrients in a marine system. When excessive levels of nitrate and phosphate are present in the water, frequent algal blooms may occur (eutrophication). Overgrowth of algae depletes oxygen levels in the water, which may cause the death of fish and larger aquatic plants. Other impacts of algal blooms include pollution, blocking of pipes and the production of odours and toxins100
4.2.2.5 Predicting the effects of exotic species
It is extremely difficult to predict the ecological effects of introduced organisms on marine systems. The success of exotic species in a new environment appears to depend upon complex interactions between the biological characteristics of the organism; the similarity of the environmental conditions to the species' natural habitat; and the level of disturbance within the new environment, with highly disturbed environments being more prone to invasion101 Introduced species which are highly visible or known predators of commercial species attract the most attention. The Committee recognises that introduced species which appear to be having no noticeable impacts on their new environment (and which may not yet be prolific), may still be causing subtle and profound changes to local marine systems102
In addition to long term changes to ecosystems caused by invasive marine species, introduced organisms can pose more immediate dangers, causing death or illness in humans and marine animals. The transport in ballast water of toxic dinoflagellates and disease pathogens is common and has had serious impacts throughout the world on human health, fishing and shellfish industries.
4.2.3.1 Toxic dinoflagellates
Dinoflagellates are single-celled alga (phytoplankton), 50% of which carry out photosynthesis. As part of their sexual life cycle, some species of dinoflagellates form resting cysts which can settle in bottom sediments and remain dormant for long periods until conditions are suitable for germination. This makes them susceptible to translocation via ballast tanks. After discharge, the cysts may also rest in sediment in port waters until favourable conditions encourage germination.
Toxic dinoflagellates may become prolific due to seasonal population explosions, resulting in blooms which can cause unsightly discolouration of surface waters (eg. red tides). This may interfere with the recreational use of coastal waters and disrupt tourism industries103
Some species of dinoflagellates produce toxins, which, when concentrated through biological magnification up the food chain, can cause sickness in and death to humans, fish, birds and other mammals. Efficient filter feeding organisms such as scallops, mussels and oysters readily accumulate toxins and can cause poisoning if eaten. World-wide, over 2000 cases of human poisoning through eating contaminated shellfish or fish occur each year104
There are a number of types of toxic dinoflagellate poisoning (Table 4).
TABLE 4
Types of toxic dinoflagellate poisoning
Type of Poisoning
Symptoms
Paralytic Shellfish Poisoning (PSP)
Muscular paralysis; respiratory difficulty; choking sensation. Potentially lethal.
Diarrhoeic Shellfish Poisoning (DSP)
Diarrhoea, vomiting, tumour formation in digestive system. Non-lethal.
Amnesic Shellfish Poisoning (ASP)
Vomiting, diarrhoea, hallucinations, short-term memory loss, seizures. Non-lethal.
Neurotoxic Shellfish Poisoning (NSP)
Gastroenteritis, rashes, death through respiratory failure in extreme cases.
There has been a global increase in the incidence of harmful algal blooms in the past 20 years, and evidence suggests that this global spread of algal species has been facilitated by ballast water and the commercial transport of shellfish105
With the introduction of exotic species there is the possibility of concurrent introduction of pathogens106 Pathogens which are capable of being introduced with ballast water include viruses, bacteria, and fungi. Such pathogens may attach to hosts as external parasites or incubating infectious diseases, or reside in tissues from dead and decaying hosts. Fish eggs with attached parasites, faeces containing parasites and viruses and other microbes may also be present in ballast water107
In November 1991, the US Embassy in London informed the International Maritime Organisation (IMO) that cholera had been found in the ballast water of three ships that visited ports on the US eastern seaboard. The ships had stopped in Latin America. Earlier that year in the port of Mobile, Alabama, cholera strains were also found in oyster and finfish samples. In June 1992, the embassy informed the IMO that cholera had been found in the ballast water of two more ships.
The CSIRO discovered Clostridium botulum C, which causes botulism in animals and possibly humans, in sediment from a Norwegian vessel that docked in Queensland after visiting Singapore108
In December 1995, AQIS published a report which reviewed the epidemiology of serious diseases of cultured and wild fish and shellfish that might result from discharge of ballast water and sediments into Australian waters109 It found that a number of pathogensi were of significant threat to Australian fisheries.
i Aeromonas salmonicida (which causes furunculosis), Infectious Pancreatic Necrosis virus (which causes infectious pancreatic necrosis), Myxosoma cerebralis (which causes whirling disease) and Renibacterium salmonarum (which causes bacterial kidney disease).
