In September, 2014, the National Marine Fisheries Service (NMFS) listed 15 Indo-Pacific coral species as
"threatened" under the U.S. Endangered Species Act. Many Indo-Pacific corals are quite difficult to
identify to species, but identification is necessary for implementation of the listings. This guide is
intended to help with identification of colonies of these species living on the coral reefs of U.S. Pacific
areas, namely American Samoa, Guam, the Commonwealth of the Northern Marianas Islands, and the
U.S Pacific Remote Island Areas (PRIA).
In all but a few cases, most coral species are defined based on their skeletal structure. Luckily, the
tissues are thin on most species, so some skeletal features can be observed in the living corals. Living
corals also have some clues that skeletons do not have, such as colors. Corals in the Indo-Pacific are
difficult to identify because colony morphology of a species can be variable and morphological
differences between colonies of different species can be small. Coral species vary in colony shape and
the features of the "corallites", which are the cups the polyps sit in ("calices" are the insides of the cups)
and other small features outside the corallites. Almost every coral species in the Indo-Pacific has one or
two other species that are very similar and hard to distinguish from it, and some have many.
Because corals species can be hard to
identify some reports can be incorrect by mistakenly identifying one species for another similar one. As
such, while known species ranges and local reports are usually good indicators of the coral fauna in a
specific area, they are not perfect, and finding unreported species is possible if not likely. In time, as scientists
learn more and refine their ability to discriminate between similar taxa, knowledge regarding species
distribution and their geographical ranges will continue to improve.
This document is a guide to the field identification of the Endangered Species Act-listed, threatened corals of the U.S.
Pacific. Species are presented in an order that groups similar corals together as much as possible, and
will present more common or widespread species at the start. In addition, other similar species are
presented to highlight the differences between taxa.
