[Coral-List] Tunicate-killing coral spreading all across Caribbean region
Thomas Goreau
goreau at bestweb.net
Wed Jan 16 16:16:31 EST 2008
Dear Alex,
The tunicate is Trididemnum solidum. This very effective coral killer
has greatly increased in many locations all around the Caribbean, but
much more in some places than others. I think the first description
of it overgrowing coral was by Chuck Birkeland when he was a post-doc
in Belize, and it was at that time a rare curiosity. 10 years ago
when I told him it was no longer a novelty and had become a big
problem, he was very surprised. I began noticing it spreading in
Jamaica around 1990. Rolf Bak began noticing its spread in Curacao
and Edwin Hernandez Delgado in Puerto Rico about 10 years ago, around
the time that I alerted Cozumel divers to it. I've seen quite a bit
of it in St. Martin, the Grenadines, Tobago, Panama, Cozumel, Turks
and Caicos, and Bonaire, where the worst infestations I have ever
seen were at the very north end of the island, with around 40% of the
coral surfaces overgrown. In some places colonies are more whitish
cream colored, or beige, but in some places they have distinct green
or blue tints due to their symbiotic cyanobacteria. For example those
in north eastern Jamaica are more blue.
There is at least one similar didemnid in the Indo-Pacfic with a
rubber mat like consistency. But the other Didemnids there look very
different, and are not thick and rubbery but thin and brightly
colored. Some are very common but do not overgrow corals, like
Didemnum molle, which can be brown and white or green and white, but
other species can grow so fast that they overgrow corals. After the
1998 high temperature mortality of corals in Indonesia, tunicates,
not algae, overgrew the dead coral very quickly, to my surprise. In
Sri Lanka in 1997 I found a green didemnid that grew so fast it was
smothering macrophytic algae, especially Halimeda.
As far as I have been able to find out from the tunicate specialists
at the Smithsonian, there seems to be little or no work on what they
actually eat, but they are presumed to eat the same sort of
zooplankton as corals. That seems to me not be correct, because there
has been a dramatic increase in their abundance and killing of
corals, and it looks as though something they can eat better than
corals can must be increasing. The fact that the highest abundances
of T, solidum in Bonaire is in a protected area with uninhabited
areas downstream with no human pollution at all implies this must be
some sort of a natural trophic shift, perhaps related to changes in
upwelling in the Cariaco Trench. For sure this pest is increasing all
over the Caribbean, but at very different rates, and the different
abundances may have some clue into changes in its food supply. What
is driving it needs to be worked out, because a lot of coral is being
killed by it. This would make a good topic for students!
Hope to catch up with you in Cocle this year, on the way to Azuero!
Best wishes,
Tom
Thomas J. Goreau, PhD
President
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
617-864-4226
goreau at bestweb.net
http://www.globalcoral.org
> Date: Wed, 16 Jan 2008 12:44:25 -0500
> From: Alex Brylske <Brylske at aol.com>
> Subject: [Coral-List] Fwd: Mat tunicate problem?
> To: coral-list coral-list <coral-list at coral.aoml.noaa.gov>
> Message-ID: <1302C019-EB0C-4D70-91E9-CACFEABC2D8A at aol.com>
> Content-Type: text/plain; charset=WINDOWS-1252; format=flowed;
> delsp=yes
>
> Received this letter from a reader, and would appreciate some insight
> from the group. Is he talking about some kind of colonial tunicate?
> Sorry, he didn't send any images.
>
> Alex
>
> Alex Brylske, Senior Editor
> DIVE TRAINING magazine
>
> Address:
> 4314 SW 18th Place
> Cape Coral, FL 33914
> Phone: 239-471-7824
> Cell: 954-701-1966
> Fax: 281-664-9497
> E-mail: brylske at aol.com
> Website: www.dtmag.com
>
>
>
>
> Begin forwarded message:
>
>> From: Roger Dunton <roger335 at comcast.net>
>> Date: January 16, 2008 12:26:47 PM EST
>> To: Alex Brylske <brylske at aol.com>
>> Subject: Mat tunicate problem?
>>
>> Alex,
>>
>> While leading a group in Cozumel this Christmas, I met a lovely
>> couple who pointed out what we believe may be a problem infestation
>> of the coral reefs. I am including their description to see if you
>> are aware of this and perhaps what might be done. They referred to
>> it as a ?MAT TUNICATE?, but it was unlike any tunicates of which I
>> am aware.
>>
>> ?First of all, we are not sure of the name, it was given to us by a
>> dive master in Belize on Turneffe Island. We have looked through
>> the name on internet but did not find anything close to it.
>>
>> Whatever its name, this algae is light grey - a bit greenish, and
>> when taken to surface it is actually a pale pink. It is thick and
>> feels rather soft to touch, like leather. It covers the coral like
>> a blanket. Actually when you look close, it seems to start with a
>> small drop, and you can see several drops like sprayed from above.
>> Each drop seems to develop into a blanket that covers the whole
>> coral head it started on, and grows along the stems of fans and
>> sponges until it covers it entirely.
>>
>> The dive master in Belize indicated that the algae should be
>> removed, or at least untucked from the coral head on the edges to
>> stop its growth. When you do this, it is sometimes easy and comes
>> in large pieces, sometimes it breaks into small crumbs. Below the
>> blanket, the coral is dead, and it seems there is only rock. There
>> are often thin spiders with long legs or long worms between the rock
>> and the algae. The algae is soft when taken off the coral, and when
>> it dries on the surface it becomes rigid.
>>
>> We have seen it a lot in Belize on the East side of Turneffe Island,
>> and we start to see it a lot in Cozumel, at about any depth. We
>> have not been able to observe a pattern, but I thought there was
>> maybe more of it in shallower waters. The weird thing is that when
>> you start looking for it, you see it a lot whereas if you are not
>> looking, you don't notice it so much.
>>
>> I would be interested in learning what it is, and what should be
>> done with it: remove it and dispose of it at surface, or just untuck
>> it, or leave it alone?
>>
>> Thank you for any light you might shed on this.?
>>
>> -Roger Dunton
>
Thomas J. Goreau, PhD
President
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
617-864-4226
goreau at bestweb.net
http://www.globalcoral.org
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