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Rocky Shore Trail
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Day in the Life of Plankton

Remember that there are two types of plankton. On any day there will be the movement of phytoplankton followed closely behind by the zooplankton.

Diatoms have diurnal rhythms in the water column. As soon as the sun is up they commence photosynthesis. The process generates oxygen and so the diatom becomes buoyant and begins to rise in the water. This causes it to move closer to the surface and gain more light for maximum photosynthesis. Of course, when the sun sets food production halts, no oxygen is formed and is used up. Buoyancy is lost and it starts to sink. If it sinks below the lit zone before photosynthesis starts the next day it will continue to sink and dies on the bottom. The herbivorous animals in the plankton will follow the food, so if the diatoms move close to the surface then the animals will not be far behind. In turn, the carnivores, like zooea larvae, will follow the herbivores.

As the phytoplankton moves and grows so it will divide by mitosis, multiplying numbers. However, this will depend on nutrients in the water like silica. If these decline then the growth slows and in time limits the density of phytoplankon. Check out what happens over a longer period of time.

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