Coral Reefs:
By Jason Ladner     Awards: Myers

Coral reefs are the most diverse and productive ecosystems in the ocean. In addition to the inherent value of this biodiversity, coral reefs confer many direct economic benefits to humanity, which have been valued at US$30 billion annually. Hard or stony corals literally form the foundation of these ecosystems.

Hard corals are colonial animals, which are closely related to sea anemones and jellyfish. However, they have formed a partnership, or symbiosis, with photosynthetic microorganisms called dinoflagellates. The dinoflagellates live inside the coral’s cells and provide the corals with energy they harness from the sun, in the same way as land plants. This symbiosis has allowed corals to form diverse ecosystems in otherwise nutrient poor deserts of the sea.

Corals themselves are also incredibly diverse, coming in endless shapes and sizes. However, surprisingly little is actually known about the diversity of corals. In the Palumbi Lab, we are using genetics in a number of different ways to understand coral diversity.

How many types of coral are there?

In short, the answer is 'more than we thought.' Corals have traditionally been categorized into species based on structural differences. However, corals have notoriously messy genetics and therefore, conventional genetic methods have not had the proper power to confirm or refute these groupings. We have been utilizing data from multiple gene regions to properly identify genetic species of coral. Our work is supporting traditional species, but is also revealing additional cryptic diversity within morphological types.  

How are coral species different?

We know that corals are extremely morphologically diverse, but we are only beginning to understand the functional differences among species. Closely related coral species have very few fixed genetic differences. This background of shared diversity makes corals an ideal system for identifying gene regions responsible for functional differences between species, as these regions will exhibit fixed sequence differences. To identify these regions we are utilizing the latest high-throughput sequencing technologies.

Why are corals so diverse?

There are likely several important factors. However, one especially intriguing mechanism is hybridization and introgression. Corals lack complete reproductive isolation among closely related species. Therefore, many coral species are able to hybridize and exchange genes. This is one of the reasons coral genetics are so messy. Hybridization can result in the formation of new species and therefore, may have contributed to the great diversity of corals. Support from the Dr Earl H. Myers and Ethel M. Myers Oceanographic and Marine Biology Trust is allowing us to test for the possibility of a hybrid origin for the cryptic diversity we have found.