The zebra mussel (Dreissena polymorpha) is a mussel that forms dense mats that clog industrial water intakes and discharge pipes. It invaded the Great Lakes in the United States. It is estimated that it will cost $10 billion to manage it over 10 years.

The comb jelly (Mnemiopsis leidyi) caused the collapse of the fin fishing industry in the Black and Azov Seas in Eastern Europe. Catch in Russia, the Ukraine, Bulgaria, Turkey, and Romania fell from 250 000 tonnes to 30 000 tonnes.

The northern Pacific seastar (Asterias amurensis) eats bivalves such as mussels. It is spreading along Tasmania's coast.

Over 2500 international vessels visit New Zealand each year at over 20 ports. Up to 3 million tonnes of ballast water is discharged in New Zealand each year.

G. catenatum was first noticed in Manakau Harbour in May 2000. Since then, it has slowly spread north and south along the west coast of the North Island, through Cook Strait, and up the east coast of the North Island into Wairarapa and Hawke Bay. When an algal bloom caused by G. catenatum is present in an area, it is closed to shellfish gathering because of the high levels of toxins in the shellfish. So far, no one has died of paralytic shellfish poisoning caused by G. catenatum. Health protection officers at your local area health board can tell you whether it is safe to eat shellfish from your area.

G. catenatum can damage the businesses that farm shellfish in affected areas because when a bloom is present, farmers are unable to harvest their shellfish. The Marlborough Sounds is the main shellfish farming area in New Zealand. The alga has not directly affected farms there because it has only reached the outer part of the Sounds. However, mussel farms in the Marlborough Sounds have been indirectly affected because farmers are unable to collect baby mussels (spat) to restock their farms. The traditional collecting areas for spat are on Ninety Mile Beach in Northland. This area is infected with G. catenatum, and so if farmers brought infected spat to the Marlborough Sounds, they might bring G. catenatum too. The shellfish industry is developing ways of cleaning the spat and looking for alternative sources of spat.

At this stage, no one knows whether G. catenatum is native to New Zealand but has not been noticed until recently or it has been accidentally introduced to New Zealand.

For more information, see:

• Algal bloom

Undaria is an exotic seaweed. New Zealand's environmental conditions suit it very well, and so it grows and spreads very quickly here. It was first discovered in Wellington Harbour in 1987. Since then, it has spread rapidly around New Zealand and is now found from Gisborne to Stewart Island. If we don't try to control it, undaria could become widespread around the North and South Islands and in more remote areas such as the Chatham Islands and the sub-Antarctic islands. It has already changed the natural character of many areas. We do not yet know what effect undaria has on native ecosystems.

The Government is doing a number of things to slow the spread of undaria, such as:

For more information, see:

• NZ Department of Conservation - Undaria - gorse of the sea?
• www.niwa.co.nz/edu/students

For more information click on any link below.

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