4.3 IMPACTS - INTERNATIONAL
Approximately 200 non-indigenous species are known to inhabit San Francisco Bay. Of those species introduced in the last 20 to 30 years, most are attributed to ballast water110 Potamocorbula amurensis, the Asian corbulid clam, arrived in northern San Francisco Bay in 1986111 Since then, the clam has risen rapidly to numerical dominance in the region.
It is believed to have permanently changed the benthic community dynamics where it inhabits the Bay by displacing former macro benthic communities. The long term-consequences of this introduction on the ecosystem are difficult to predict, particularly as little is known about its environmental tolerances, food requirements, reproductive biology or relationships in its original Asian habitat112Following the recent introduction of Carcinus maenas, (European shore crab) into San Francisco Bay, and its rapid spread, it is believed that it could "fundamentally alter the distribution, abundance and species interactions of the San Francisco Bay intertidal and subtidal faunas"113
In 1990, it was thought that 27 of 69 documented exotic species introduced into the Great Lakes system in Canada and the United States were introduced via ships' ballast water114 By 1995, 137 species were known to inhabit the Great Lakes. Harmful exotic species include a European perch-like fish, Gymnocephalus cernua, the river ruffe; a predacious planktonic cladoceran, Bythotrephes cederstroemi, the spiny water flea; and Dreissena polymorpha , the zebra mussel.
It has been estimated that annual losses of more than $US90 million will occur in fisheries, for two species alone, if the exotic river ruffe spreads outside its current limited range115
The zebra mussel is thought to have been introduced into Lake St Claire in late 1986116 The subsequent appearance of isolated populations of the mussel in numerous harbours throughout the Lakes suggest that they have been dispersed through commercial and recreational vessels (fishing activities, ballast water and pump through toilets etc.). Boat hulls have also been shown to be potential vectors for transporting juvenile mussels117 The mussel is now found in all large river intakes leaving the lakes. By way of rivers and canals, it has reached as far as New York in the east, Louisiana in the south and Okalahoma in the west118 It has also established itself as a fouling organism in lakes and rivers.
The zebra mussel has caused major disturbances in the marine ecosystem including declines and extinctions of native mussel populations. Zebra mussel infestations have also resulted in clogged municipal and industrial water intake pipes, particularly by blocking water intakes to thermal and hydro-electric stations. It is estimated that by the year 2000, costs of measures against the mussel will be in the order of $US5 billion119 Others estimate that the cost of keeping water intakes from the lakes free of mussels will be in the range of $US2-4 billion per year120
Mnemiopsis leidyi, the American Atlantic coast comb jelly, was introduced via ballast water into the Black and Azov Seas in the early 1980s. Its numbers expanded rapidly, resulting in a severe decrease in zoo-plankton biomass and the virtual extinction of anchovy fisheries. By 1990, the total biomass of the comb jelly had reached an estimated 900 million tonnes, ten times the total annual fish catch from all the world's oceans121 It is estimated that the comb jelly now has a yearly biomass production of over 100 million tonnes122
The comb jelly has affected fisheries by reducing the food available to fish, by clogging fishing nets, and by feeding on fish eggs and larvae. Stocks of some formerly commercially valuable fish have been destroyed in the Azov Sea, and losses to fisheries are estimated at $250 million dollars in the Black Sea alone123 Long term, it is thought that predation by the comb jelly on the planktonic larvae of benthic invertebrates may change the composition of benthic communities, in turn adversely affecting shellfish fisheries.
The comb jelly has formed large concentrations in the Sea of Marmara and also near Mersin, Turkey. It is likely to establish populations in other estuarine regions of the Mediterranean and may already have been transported to other parts of the world124
A number of fouling species have caused economic problems in the Baltic Sea. These species include the zebra mussel Dreissena polymorpha; the barnacle Balanus improvisus; and the hydroid Cordylophora caspia. In some areas (along the Finnish coast and in the Gulf of Riga), they have clogged the water intakes to power stations and other installations125
Since the 1970s, blooms of toxic dinoflagellates have occurred on the Swedish west coast resulting in the closure of commercial mussel farms for long periods of time.
A number of polychaete worms have been introduced and become established on both the Swedish coast and in the Baltic Sea. In some places they have become the dominating species, for example, in the Vistula lagoon, Marenzelleria viridis, the North American polychaete, makes up 97% of bottom-living macrofauna126
Over sixty exotic species of algae have established in Mediterranean waters since the turn of the century. To date, no major impacts from these species have been reported, although a recent introduction, Caulerpa taxifolia (Caulerpa), is posing serious threats to Mediterranean ecosystems127
In 1984, off the French coast between Marseilles and Nice, Caulerpa was discovered in an area measuring one square metre. By 1996 the area covered by the algae was estimated to be 30 square kilometres. The algae, which has been described as a "monster", is believed to be a mutant strain of a tropical species, and is thought to have been introduced into the Mediterranean when an aquarium was emptied into the sea128 The algae is being spread throughout the Mediterranean by recreational and fishing vessels, and has now been found on the coasts of Italy, Spain, and Croatia129 Caulerpa grows up to six times the size of the tropical variety, and creates dense forests which exclude native flora and fauna. It produces toxins, can grow in polluted or pristine waters, and despite its tropical origins, survives the harsh Mediterranean winters. Caulerpa has no local predators130
4.3.6 New Zealand
Undaria pinnatifida (Japanese kelp) was first discovered in New Zealand in Wellington Harbour in 1987131 Subsequently, it has been found in at least seven other locations in New Zealand waters, including on ropes and sea cages in marine farms132 The kelp's spread around New Zealand has been attributed to both ballast water and ships' hulls. It has been shown that the kelp can survive journeys on ship's hulls in extreme sea/weather conditions in New Zealand waters133 It is not clear how much of an impact Japanese kelp will have in New Zealand.
Codium fragile tomentosoides (Codium) is a native of Japan. Commonly known as green sea fingers, it was first recorded in New Zealand in 1973 and is believed to be responsible for the decline of shellfish beds134
In 1992/93 New Zealand experienced severe algal blooms, and in 1993, the New Zealand shellfish fishery was closed for three months due to an outbreak of Gymnodinium breve which causes paralytic shellfish poisoning. Subsequently, a million dollar program was implemented to provide adequate monitoring for future blooms. While there is no direct evidence to show that the organisms which caused these outbreaks were introduced in ballast water (or introduced at all), it is now well known that toxic dinoflagellates are commonly transported around the world in ballast tanks135
