How do marine environments change by plate tectonic action?

The diversity of life over the globe can be measured by the number of species that occupy a given habitat or area. Many factors affect diversity, including the available energy supply in the area, the number and variety of the different microenvironments that can be occupied by different species, and the severity of the physical environment. But some factors seem to affect diversity levels more strongly than others.

On the Earth today there is a strong diversity gradient from pole to equator among communities of organisms living in the shallow seas and on land. Many more species live in tropical communities than in high-latitude communities, and the average number of species in any community falls off toward the poles even over a few degrees of latitude. This trend has been documented for many groups of organisms, from birds to bivalves and from foraminiferans to orchids.

Many explanations have been suggested for the diversity gradient, but generally they relate to the fact that the environment is much more seasonal toward the poles. At the equator, the day length never changes much from a twelve-hour day-night cycle; at each pole there is for practical purposes only one day and one night per year, with three months of full daylight, three months of complete darkness, and two three-month periods of twilight in between. Environmental conditions fluctuate greatly in polar regions, especially the supply of food that comes directly from photosynthetic plant production on land and in the sea. Only relatively few organisms have adapted to live successfully in such an extreme set of conditions. What is the connection between seasonal light intensity and low diversity?