Coral Species Diversity and Conservation Challenge in the U.S. Pacific Ocean

by Jim Maragos, Ph.D., Coral Reef Biologist, U.S. Fish and Wildlife Service, Honolulu & Member, Coral Specialist Group, Species Survival Commission, IUCN
photographs by Russell Moffitt

The Pacific Ocean supports the largest and among the oldest habitat for coral reefs, and the United States now manages the largest array of protected coral reefs in the world. Especially during the past century, coral reefs have been increasingly threatened by the activities of mankind, but now population growth, unmanaged fishing, and climate change will pose as more severe threats to coral reefs during the next century. Stony corals and coralline algae are the main life forms responsible for the biogenic growth and maintenance of reefs worldwide, yet we are only now focusing attention of the status of threats to these principal reef builders. Most reef corals consist of thin living animal tissues over a stony skeleton, and most are colonial and dependent upon single celled plants (called zooxanthellae) that live in their tissues for growth and nutrition. As such, these factors complicate efforts to define coral species and determining which are under threat and warrant special protection.

Scientific description of corals began with Linnaeus in 1758, and for most of the following century, definition of coral species relied on dead skeletons, written descriptions, and sketches. Although this approach has been successful for higher non-colonial animals such as birds, mammals and reptiles, corals altogether lack the prominent diagnostic features of these species such as eyes, noses, beaks, limbs, heads, tails, ears, faces, consistent coloration, etc. Moreover, the English language has mostly evolved in regions lacking corals, requiring Latin derived words as the basis for describing them, further confounding the understanding of the terms by which corals are separated into different species. Since 1850, photographs accompanied the published description of coral species, but virtually all of these were of the dead, cleaned skeleton of corals, with description of living tissues still relying on artistic sketches and written descriptions. As a consequence there were many more coral species described than what actually occurred in nature due to the lack of sufficient information to distinguish them.

Over the past several decades, scuba diving and guide books with colored photographs of living corals have helped many scientists learn coral species underwater where they live. Nevertheless, the colonial nature of living coral allows many to change their growth form to better adapt to differing habitats, and there are still concerns over which coral descriptions are the real species and which are “junior synonyms” of them. Over the past half century coral taxonomists have grappled over alternative means to describe individual species including numerical taxonomy of morphological features and immunoassay techniques to distinguish closely related species. However, these have met with limited success. More recently, molecular approaches that compare the DNA of different corals are showing great promise in determining which morphologically similar species have differing genomes and which corals with differing growth forms have the same genomes. As more “markers” are discovered on genes, there should be greater success in defining coral species. However, there will still need to be a strong relationship between consistent morphological-anatomical characteristics and molecular characteristics to resolve the coral species dilemma, and determine which are in greater need of protection.