The isolated location of Bermuda has had a marked effect on the corals that surround the island. At a latitude of 32°N, Bermuda barely makes it into the acceptable temperature range for coral growth. Bermuda lies at a similar latitude to Savannah, Georgia on the east coast of the USA, where it is far too cold for corals. Why then does Bermuda have warm enough waters for corals to grow?
Bermuda’s warmer than usual waters, for its latitude, are due to the Gulf Stream, a huge ocean current that flows north from the Caribbean, up the Eastern seaboard of the USA and past Bermuda. It provides a continual source of warm seawater and with it sub-tropical climate conditions. The Gulf Stream also brings a collection of Caribbean floating terrestrial and marine organisms, including coral larvae. The incredibly long journey means most coral larvae do not make it, while others cannot withstand the colder temperatures as they move north. Therefore, the small subset of corals that do grow in Bermuda, are at their northern-most limit and show a much lower species diversity than their counterparts growing in the Caribbean region.
The Gulf Stream appears to have brought coral larvae to Bermuda for millions of years and coral reefs were among the first ecosystems that developed around this isolated island. These coral reefs were important in assisting the development of shallow-water, and then land habitats, in the area. Over 1000's of years the sea rose and fell, as sea levels rose some reefs struggled to keep up and 'drowned in the dark', and then the sea levels fell leaving some reefs exposed, again some reefs perished during this event. It was the continual flow of coral larvae that rode the Gulf Stream which rejuvenated the reefs, making them the impressive sights we have been surveying on the Catlin Seaview Survey.
Many thanks to Alex Venn of BIOS research station for the image.