[Coral-List] Exotic vs. Invasive.

Ken Marks data at agrra.org
Fri Feb 15 12:37:38 EST 2013

On 2/15/2013 11:26 AM, John Ware wrote:
> Ken Marks recent post concerning Tubastraea micranthus reminded me of an
> incident that occurred on a recent trip to Bonaire.  A divemaster was
> bemoaning the "invasion" of lionfish.  When I mentioned that the "poster
> coral" for Bonaire (Tubastraea sp) was invasive, I was severely
> chastised.  Lionfish were "invasive", Tubastraea was "exotic".
> I noted that Ken Marks used both "exotic" and "invasion" in his e-mail.
>   I had never thought about the distinction before.
> After Googling around a bit, I concluded that if the species under
> consideration was sort of cute, it was "exotic".  If it was ugly, it was
> "invasive".
> While that is a vast oversimplification, I wonder if the coral-reef
> community distinguishes "exotic" from "invasive" and, if so, is there a
> precise definition of the difference?
In my previous post I likely used both terms merely as a means of 
sounding less repetitious.

In my mind "exotic" is what might also be thought of as "alien" or 
"foreign" in the sense that it is not native to where it is found. A 
zebra would be an exotic species in a Florida zoo but not on the plains 
of Africa. That being said, a Floridian like myself might dream of 
traveling to Africa to see these "exotic" animals in their native 
environment. This hints at a secondary definition of exotic meaning 
"exciting" or "unusual" which likely dates from the Victorian age (or 
earlier) when "exotic" plants and animals were brought from their native 
lands to become curiosities in foreign lands.

Exotic species are spread in may ways, intentionally and otherwise, and 
through various vectors. The small dorid nudibranch /Thecacera pacifica/ 
which is not surprisingly (given its name) native to the Pacific, can be 
found rarely at the Flower Garden Banks in the Gulf of Mexico. As this 
is along the route of major shipping lanes the vector is likely passing 
ships. This little (1") species (so far) has not exploded in numbers in 
its new territory and doesn't yet seem to be significantly altering the 
ecosystem or unduly competing with or preying upon native species to the 
point where it would be considered "invasive".

In my mind there are stages to the "non-natural" spread of a species:

1) Exotic - The species is found outside of its naturally occurring 
area. The garden centers of all "big box" retailers are rife with exotic 
plant species.

2) Naturalized - Once a population starts reproducing itself in its 
non-native range I would consider it naturalized. Lionfish were 
intermittently released (accidentally or, sadly, on purpose) in Florida 
for decades but it took years for this species to reach the tipping 
point where it was able to effectively breed here. Once a species starts 
procreating I would consider it naturalized to the area.

3) Invasive - If a naturalized exotic species is very fecund and/or is 
aggressive in its takeover of a new habitat it becomes invasive. There 
have been rhesus macaques in Florida where they were released in the 
1930's by a tour boat operator looking to make the "Jungle Cruise" 
experience more exotic (literally). These macaques have become 
naturalized in certain areas where they have found it meets their needs 
but (to my knowledge) have not crossed the threshold where they would be 
considered "invasive". Burmese pythons on the other hand have 
established themselves in the Everglades region of South Florida and 
have had a devastating effect on the populations of native species 
(especially mammals).

I think people are willing to overlook the invasiveness of a species 
(/Tubastraea coccinea/) if it is "cute/pretty" and they don't notice or 
care about the displacement of native species caused by the invader. 
There is no denying that underwater photographers like taking pictures 
of wrecks festooned with bright orange /Tubastraea /and so in some sense 
it could be argued that it is not problematic for tourism where it is 
found. If instead of a picturesque cup coral we were instead invaded 
with a nasty stinging hydroid or box jelly I think the attitude to the 
invader would be less welcoming.

Anyway, that's my two cents. Others may choose to comment on this or 
correct me as necessary.

Ken Marks
AGRRA Data Manager

More information about the Coral-List mailing list