Protozoa are one of the simplest forms of life in the sea.   In their most basic form they resemble the structure of a raw egg – with a “nucleus” (the yolk of the egg) carrying their genetic material, surrounded by a lump of “protoplasm” (the raw white of the egg).

Protozoa can be animal or vegetable by nature and belong to either the “zooplankton” of drifting ocean animals ranging in size from tiny protozoa to giant swarms of jellyfish, or “phytoplankton”, the tiny floating plants of the sea.

In Irish waters, protozoa are hardly noticed at all unless they multiply so rapidly that they form “plankton blooms” which colour the water in which they live. Some of the species that “bloom” in Irish waters can contain tiny amounts of toxin which, when concentrated in the stomachs of filter-feeding shellfish such as oysters and mussels, can be harmful to consumers. That is why the Marine Institute maintains a monitoring services that takes samples of water from the main shellfish growing beds around Ireland and issues warnings to shellfish growers, the Department of Agriculture, Fisheries and Food and the Food Safety Authority of Ireland, if any dangerous plankton are found.

Most protozoa are perfectly harmless however – even one that glows in the dark. Noctiluca scintillans is a commonly occurring zooplankton that has the ability to generate biological light by mixing two natural chemicals within its body when disturbed. This “bioluminescence” can create a wonderful natural firework show in the seas around Ireland , particularly in the late summer and early autumn when Noctiluca blooms are most likely to occur.

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