Marine diatoms are unicellular algae that are found in all oceans. They are responsible for about 20% of the world's primary production, making them one of the most important groups of organisms on the planet. Diatoms have a unique cell wall made of silica, which is called a frustule. The frustule is made of two halves, called valves, that are held together by a girdle. The valves are covered in tiny pores, which allow water and nutrients to enter the cell.

Diatoms are able to survive in a wide range of light conditions, from very low light to very high light. They do this by changing the amount of chlorophyll in their cells. Chlorophyll is a green pigment that absorbs light energy and uses it to photosynthesize. When light levels are low, diatoms produce more chlorophyll so that they can capture more light energy. When light levels are high, diatoms produce less chlorophyll so that they don't get too much light energy and damage their cells.

In addition to changing the amount of chlorophyll in their cells, diatoms can also change the shape of their frustules. When light levels are low, diatoms produce frustules that are more rounded. This allows them to capture more light energy from all directions. When light levels are high, diatoms produce frustules that are more flattened. This helps to reduce the amount of light energy that they capture, and it also helps to protect them from damage.

The ability of diatoms to adapt to fluctuating light conditions is essential for their survival. It allows them to live in a wide range of environments, from the open ocean to the depths of the sea. Diatoms are a key component of the marine ecosystem, and their ability to adapt to changing light conditions helps to ensure that they will continue to be a major player in the future.