Harry et al.,

A healthy start indeed. Let's consider what is implied by a Gulf of Mexico
endemic, that is, a species restricted to the Gulf of Mexico. This would be
a species that needs Gulf conditions (cooler than the Caribbean, say, or
perhaps restricted to the mouths of great rivers like the Mississippi, or
dependent on plants or animals that grow here). Or maybe it's not quite so
fussy, but has been wiped out on the Atlantic side of Florida, Georgia, and
the Carolinas north to Cape Hatteras (which have similar climate and
submarine conditions). In view of the wreckage left by hurricanes, maybe we
should also consider this fauna as being a set of survivors, with
characteristics that allow these species to withstand waves and turbidity.

Together, these warm but temperate shallow waters comprise the Carolinian
province, which is roughly equivalent to the waters along coasts that
support live oaks (Quercus virginianus). During the coldest parts of the Ice
Ages, this maritime region stayed relatively warm and today hosts a
remarkable relict flora with many endemic trees and other plants. Shouldn't
we ask also which species are endemic to the Carolinian province, as well as
to the Gulf part of it?

How long has the Florida barrier been there? Long enough for species or
subspecies to differentiate on either side? At present, Florida extends so
far south that its southern tip is tropical and bears a flora and fauna much
like Cuba's.

For sand-dwelling shallow-water species whose larvae cannot drift on the
currents, the muddy Mississippi Delta is a formidable geographic barrier,
and it was even more a barrier during glacial periods, since the Mississippi
River was pouring vast amounts of cold glacial meltwater into the Gulf. What
species or subspecies are now restricted to one side or the other of the
Mississippi River? The river has been there without interruption for a very
long time, tens of millions of years at least, and I doubt if it ever ran
clear.

Please give these geologic-geographic ideas some thought overnight and let
us know what you think.

Andy

Andrew K. Rindsberg
Geological Survey of Alabama

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