[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,

Thomas J. Goreau, PhD
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net

> 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
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net

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