Key Ideas about Toxic Algae Blooms

• Shellfish, like oysters, mussels, and cockles, feed on very small plants that float in the sea (the phytoplankton). Dinoflagellates are one kind of microscopic algae and of the thousands of species, only a few kinds release water-soluble poisons that can kill other species of marine life. When shellfish eat the toxic dinoflagellates, the poisons become concentrated in them. If people eat the shellfish, they can become very sick and even die from the concentrated poison.
  
  
• To see the various kinds of toxic dinoflagellates in New Zealand, click HERE.
  
  
• Dinoflagellates are plants but they also swim using a long whip-like extension called a flagellum. They are very small, about 0.02 to 0.04 millimetres in diameter, and shaped like a soccer ball with a groove around the equator.
  
  
• In 1982-83 thousands of fish and penguins died in the Hauraki Gulf. The significance of the event went unremarked at the time except for the Ornithological Society. Later reports of dead fish, blamed on fishing trawlers, coincided with reports of numb lips and swollen tongues from shell fish lovers in Waiheke Channel and the Firth of Thames estuary. Then, in 1986 and 1987, across the Tasman Sea in Tasmania, a massive outbreak of shellfish poisoning was traced to toxic dinoflagellates formerly thought to be limited to the east coast of the United States and Japan's Inland Sea.
  
  
• Some researchers believe the toxic species were accidentally introduced. Many ships arrive in Australia and New Zealand from Asian ports with very little cargo. To keep their propellers in the water, large ships pump up to 50 million litres of sea water into their ballast tanks. The water contains plankton from some of the most polluted harbours in the world. When they arrive, the ballast water is pumped out and cargo is loaded. Researchers sampled the ballast water of one visiting ship and found more than 30 million live toxic dinoflagellates.
  
  
• In 1989, a New Zealand salmon farm on Stewart Island, with $12 million dollars worth of salmon, was wiped out in a few days by a toxic algae called Heterosigma akashiwo. In 1992, outbreaks of massive numbers of toxic dinoflagellates, broke out in many areas of New Zealand. More than 200 cases of poisoning were reported in the summer of 1993. Symptoms included diarrhoea, vomiting, muscular aches, dizziness, loss of memory, tingling, numbness of the lips and respiratory problems.
  
  
• Toxic dinoflagellate blooms continued during the summer months of 1993, 1994 and 1995. More than six species of dinoflagellates were identified in these episodes. The most common species was formerly limited to the south-eastern United States.
  
• Dinoflagellates have an efficient reproductive strategy. When conditions favour growth, they reproduce swiftly, by binary fission. But when conditions are bad, they reproduce sexually and form cysts which settle on the sea floor and await - often for years - return of favourable conditions. When nutrients and temperatures favour the organisms, the cysts burst open and the population soars, filling the sea with thick, soupy masses of these swimming plants. They excrete toxins to kill zooplankton and fish predators. The toxins vary from species to species but are among the most virulent poisons known. Thousands of fish and other organisms may be killed when population densities become very high.
  
  
• Researchers suggest ocean outfalls of sewage from urban areas, agricultural fertilisers, and cocktails of biotoxins from agricultural areas all contribute to ideal conditions for the dinoflagellate blooms. Although ships have been bringing toxic species into New Zealand waters for many years, and toxic species probably occur here naturally, the set of conditions for massive outbreaks seems to be relatively new.
  
  
  
• When there is a bloom of algae, there can be more than 900,000 of them in one litre of sea water, and they colour the water brown or red depending on what species are present.
  
  
• The Ministry of Fisheries and local health boards test shellfish meat for marine biotoxins to alert people to dangerous toxic algae blooms. Cawthron Institute in Nelson carries out plankton analyses to alert the oyster industry of potentially hazardous conditions. When poisons are found in the shellfish, or blooms of toxic dinoflagellates reach dangerous levels, the areas are immediately closed to further collecting and the public is warned not to eat shellfish until the poisons have vanished again.
  
  
• Green Shell Mussels can rid themselves of toxins in about three weeks, but Tuatua and Pipi may retain some kinds of toxins for years after a serious toxic algae outbreak. Biologists believe the Tuatua and Pipi might actually concentrate the poisons in their siphons to discourage birds and fish from biting them.
  

Resources to use

Wild South Videos: Giants of Ningaloo (Whalesharks off the reefs of Australia.)

School Journal: Mussel Farming-1984 Part 3 no.3 11-13

Oysters------------1975 Part 1 no.2 9-10

New Zealand Geographic Magazine #3 Oysters and #18 Greenshell Mussels

Microsoft Oceans CD. Section on Plankton and Shellfish

Newspaper stories about poisonous shellfish, especially in 1993.

Most references to toxic algae are of Tertiary level and difficult to find. Schools interested in working with Lesley Rhodes on Toxic Algae Blooms can write for copies popular publications on Toxic Algae. Address requests to: Jenny Ragg at the Cawthron Institute Private Bag 2, Nelson