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Rocky Shore Trail
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A Year in the life of Plankton

On a daily scene we saw the movement of plankton and the phytoplankton multiplying by binary fission so that the density increased rapidly. Well, this can only happen if there is sufficient nutrients present.

Plankton Blooms

The amount of plankton is far from constant. In fact there tends to be two peaks in a year. The first and largest occurs in spring and the second smaller one is in the autumn. These peaks coincide with prolonged wind and gales blowing across stretches of open water. The ensuing wave action stirs the water.

Both nutrients and the propagules of the plankton will be lying in the sedimet on the bottom of the sea (the benthos) out of the reaches of the sun. The lack of light here prevents growth and development. The disturbance of the sediment by water movement will bring the propagules and nutrients, like silica, into the lit zone. Diatoms and dinoflagellates will be better able to grow with the increase in nutrients. They photosynthesise, grow and multiply over weeks. This "bloom" can be visible from space and there are photos of such blooms on the NASA website taken from Space Shuttle flights.

The visibility in the water can be drasticly reduced as it becomes like pea-soup! The blooms that occur in spring and autumn will coincide with teh reproduction of many seashore animals. By synchronising their release of larvae they are ensuring that there is plenty of food for their progeny. Barnacle nauplii larvae, typically, are most abundant in March and April. Limpets release their off spring in late September and October.

Remote sensing of phytoplankton is used by oceanographers to maintain a global view of the oceans. The pigments of the phytoplankton interact with light in ways that can be detected from space by means of satelliteborne sensors called radiometers. More information and images at


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