Toxic Algae Activities
- Look up newspaper and magazine articles about toxic algal
blooms. Discuss the fact that they were never seen in New Zealand
- Write a report on a local toxic algae bloom and how it effected
the people in your community.
- Collect some shellfish - oysters, cockles, pipi or mussels
- without harming them and put them into a small aquarium or clear
plastic food containers. Use two to three shellfish per litre
of aquarium. A small air-stone with an air pump will assure their
water has enough oxygen. Observe their behaviour after they have
- Most shellfish that live between the tides open their valves
to feed about two hours before high tide. Those that live buried
in the sand, like Cockles and Pipi, will open their shells and
extend two siphons. They pump water in through one siphon
and out through the other. Mussels and Oysters simply open their
shells and begin pumping water through siphons that do not extend
from their shells. Sometimes they release wastes through the excurrent
- When the shells are open or siphons extended, carefully add
drops of carmine solution to the water. Observe the shellfish
pumping water. They will eventually clear all of the red particles
from the water. Time them and see how long it takes them to clear
the water. If you add more shellfish to the container do they
clear the water faster? If you add more drops to the water does
it take them longer?
- If the tiny red particles of the carmine solution were toxic
algae, where would they wind up?
- After they have fed for a time, transfer the shellfish to
a clean aquarium and let them rest. After awhile, perhaps overnight,
look for the red matter coming out of their siphon or out of the
opening in their shells. They cannot actually digest the red carmine
particles and so they clean them out of their system. How does
this compare to shellfish cleaning their system of poisons from
- Why do shellfish like cockles and pipis have long siphons
compared to mussels and oysters? Carefully add a drop of food
colouring to the water near the siphons (if you move too fast,
what happens?). The dye will be sucked into the incurrent siphon
and ejected from the excurrent siphon. Which one is which
and how can you tell them apart?
- Where do people collect shellfish? Interview older people
in a community near the sea to talk about shellfish populations
today compared to when they were young.
- Where do people farm shellfish? What kinds of shellfish are
farmed in New Zealand and how is this done? Perhaps you can arrange
a field trip to a shellfish farm or ask a shellfish farmer to
talk to your school and demonstrate the process.
- Where have there been outbreaks of shellfish poisoning? Research
this in the library by looking up newspaper articles since 1992.
- The species of toxic dinoflagellates are about 0.03 millimetres
in diameter. How big is that? If one of these creatures was on
your thumbnail and was enlarged to the size of a marble (say 18
millimetres) how big would your thumbnail be? How many dinoflagellates
would fit on the head of a pin? On the full stop at the end of
- Observe the base of the food web. Obtain some brine shrimp
eggs at a pet store (sea monkeys) and a species of algae used
in aquaculture (Tetraselmis). Observe the development of the green
"bloom" of the microalgae in flasks or plastic bags.
Hatch the "sea monkeys" or brine shrimps and observe
them feeding and growing under a stereo microscope. Cawthron Institute
can provide small capsules of Tetraselmis with a media
recipe and instruction sheet.
- If a microscope is available, collect some water from a river
or the sea and look for microalgae and microscopic animals.
- To identify New Zealand's toxic dinoflagellates, click HERE.