Dayna Isherwood, of South New Brighton School, asks :-

What do oysters eat?

Sean Handley, a marine ecologist with the Cawthron Institute, Nelson, responded.

Oysters eat very small food items found in the sea. They mostly eat the tiny single-cell plants that float around in the sea and give the sea its colour. These plants are so small that you need a microscope to see them.

You may well ask - how do oysters eat such tiny plants? Well, they filter and collect these plants with their gills. Oysters have two gills which cover either side of their body like lying between two blankets in their shell. These gills are covered with very fine hairs which can beat in rhythm to produce a current of water to pump the seawater in and out of the oyster. The surface of these gills is covered with sticky mucus which the tiny marine plants get stuck to. The food trapped on this mucus is moved by more tiny hairs over the gills to the oyster's mouth.

Surprisingly, oysters can also eat mud! If the beach where oysters live is very muddy, waves often stir this mud up with the water. This mud can also contain tiny plants and bacteria which the oysters can eat. If the seawater becomes too muddy however, the oysters gills can become clogged and they may stop feeding.