The situation is complicated a bit with ongoing changes caused by
humans (global warming, building novel structures such as oil
platforms in otherwise soft sediment environments, etc.)  A species
may get to a place that it couldn't live before but now finds
hospitable.

Is the prior fauna to be so well documented as to prove that something is new?

Some species have thrived for a while in a new area, only to die out,
while many others have become established.  It probably takes waiting
a while to see if the new population is truly stable.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

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