[Coral-List] Tunicate-killing coral spreading all across Caribbean region

rbak at nioz.nl rbak at nioz.nl
Thu Jan 17 03:00:06 EST 2008

Dear collegues,

We have been looking at the compound ascidian Trididemnum solidum  for 
some time now and this work is ongoing.
For some info on Ts  biology see our earlier work such as;

Bak, R.P.M., Lambrechts, D.Y.M., Joenje, M., Nieuwland, G., Van Veghel, 
M.J.L. 1996. Long-term changes on coral reefs in booming populations of a 
competitive colonial ascidian. Mar.Ecol. Prog.Ser. 133: 303-306

Van Duyl, F.C., J. Sybesma and R.P.M. Bak. 1981. The ecology of the 
tropical compound ascidian Trididemnum solidum (Van Name) I. Reproductive 
strategy and larval behaviour. Mar. Ecol. Prog. Ser. 6: 35-42.

Bak, R.P.M., J. Sybesma and F.C. van Duyl. 1981. The ecology of the 
tropical compound ascidian Trididemnum solidum II. Abundance, growth and 
survival. Mar. Ecol. Prog. Ser. 6: 43-52.

Sybesma, J., F.C. van Duyl and R.P.M. Bak. 1981. The ecology of the 
tropical compound ascidian Trididemnum solidum (Van Name) III. Symbiosis 
with unicellular algae. Mar. Ecol. Prog. Ser. 6: 

Bak, R.P.M., Joenje, M., de Jong, I., Lambrechts, D.Y.M., Nieuwland, G. 
1998. Bacterial suspension feeding by coral reef benthic organisms. 
Mar.Ecol.Progr.Ser. 175: 285-288

So you see the ascidian was around for some time since I first saw it 
becoming numerous in the mid 70'ties.

Best regards,

Prof. Dr. Rolf P.M. Bak
rbak at nioz.nl
tel +31 222 369541
fax +31 222 319674
Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59
1790 AB Den Burg, Texel
The Netherlands

Thomas Goreau <goreau at bestweb.net> 
Sent by: coral-list-bounces at coral.aoml.noaa.gov
16/01/2008 22:16

coral-list at coral.aoml.noaa.gov

[Coral-List] Tunicate-killing coral spreading all across Caribbean region

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; 
>                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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