[Coral-List] Biorerosion has been recognized for a long time

Thomas Goreau goreau at bestweb.net
Wed Oct 18 13:28:52 EDT 2006

Dear Mike,

You are right to bring Bioeresion up again. This is yet another  
astonishing case of something that has been very well known for many  
decades somehow entirely escaping the attention of current  
researchers in the field. In Gpreau, Goreau, and Goreau, Corals and  
Coral Reefs, 1979, Scientific American, (but written about 10 years  
before), reef growth as the balance of coral growth against bio- 
erosion, and in particular the role of Cliona, was clearly  
emphasized, because this was common knowledge in the field long  
before that.

Best wishes.,

-----Original Message-----
From: Michael Risk [mailto:riskmj at univmail.cis.mcmaster.ca]
Sent: Tuesday, October 17, 2006 9:24 AM
To: Gregor Hodgson; jrohde at msh.org; coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Michael Risk - C. delitrix as measure of

Hello Gregor.

This response may be more than you had bargained for, but you asked for
it. Part of what I have to say has just been covered by Christine
Schoenberg?s post: Christine REALLY knows boring sponges, whereas I
just dabble.

It is gratifying to see interest in bioerosion now. That the coral reef
biological community could so assiduously have ignored a process that
controls their ecosystem is something that is beyond my ken-but then,
so are a lot of things.

Boring sponges are the main culprits. As their activities are
accelerated by elevated levels of nutrients in surrounding waters, it
is appropriate that they be included, where possible, in monitoring

There are two species of possible interest, Cliona delitrix and C.
orientalis (aka caribbaea, viridis, etc.) To begin with delitrix : the
specific name comes from the Latin ?to destroy? (?Cartago delinda est,?
etc), and has the same root as the Delete key on your computer. It is
one of the few sponges having the ability to settle on live coral
tissue, establish, and spread from there. (Most of the others have to
land on bare substrate first.) More than 20 years ago, in the dark ages
before pdf?s, we established a relationship between abundance of this
sponge and amount of fecal bacteria in the water (Rose, C.S., Risk,
M.J., 1985. Increase in Cliona delitrix infestation of Montastrea
cavernosa heads on an organically polluted portion of the Grand Cayman
fringing reef. Marine Ecology 6 (4), 345?363). Montastrea cavernosa
continues to be its favorite prey/host, by the way.

Since then, I have seen this sponge everywhere in the Caribbean where
sewage pollution is a problem. Off the east coast of Florida, the
characteristic ochre-red colour of C. delitrix colonies 10?s of meters
in extent in shallow water may be seen from low-flying aircraft! In
another recent example, I was trying to survey the fringing reefs of
Grenada. I was in a small boat, a local kid (anyone under 40, in my
case) guiding me. At one point, I found a large colony, explained to my
guide what it was and why I was looking for it. He then took me to the
next site. I was under water maybe 30 seconds, popped back up saying
?What the ****?? (not being able to use expletives on coral-list), to
meet my guide grinning ear to ear. He had taken me to the bay receiving
drainage from the town dump, which could not be seen from the boat: and
I had just seen a reef on which close to every head was infested.

In life, the critter is bright ochre-red. I will send you by separate
email some photos: any other ?list readers may also request copies.
Colony size ranges from tiny to very large: the biggest I have
personally seen would be 2x3m (Florida Keys). Patches the size of an
open hand are sometimes common. M. cavernosa is usually the first to be
attacked, but eventually it will munch everything in sight. Sometimes
it is colonised by white commensal zoanthids, the name of which escapes
me (if I ever knew it).

My first dive on the reefs of Florida was in 1960, and my eyes must be
failing because it doesn?t look the same now. It has been said by some
that the Florida decline is due to ?climate change.? This is
politically- and economically-motivated pernicious foolishness, and
should be challenged whenever encountered. In fact, a number of very
fine scientists (Halas, Dustan, Shinn,...) have documented that the
decline in Florida began in the 70?s, long before any wiggles in ocean
temperature, upticks in pH, etc. Two previous works documenting the
trajectory of the Caribbean-wide decline (Pandolfi et al, Gardner et
al) also clearly show that the downward slide began some time ago, and
that there is no notable recent acceleration correlating with any
climate Hockey-Stick curve, or any other ?climate-change? related

Make no mistake: if climate change is not halted or reversed, it will
in all likelihood slay every reef on the planet-but by then, what
remains will be poor remnants of those glories some of us remember. No,
if we wish to confront the real cause of the deaths of our reefs we
need to look in the mirror when we flush the toilet (a riveting image
if ever there were one.) To add to the body of evidence already in the
literature, there is a growing mountain of evidence implicating
nutrients/sewage/eutrophication. This thread was prompted by the
discussion of the recent, and excellent, paper by Kuffner et al,
showing how macroalgae inhibit coral settling. There was previous
discussion of the Cline et al paper (MEPS 314: 119?125) on the impact
of DOM on coral-inhabiting bacteria, and how this disrupts the
coral-algal symbiosis. Brian Lapointe?s body of work simply cannot be
ignored, and there is also corroborating work from biomarker studies
(Downs et al, Environmental Forensics 7:15?32, 2006) and geochemical
indicators (Ward-Paige et al, 2005: Mar Poll Bull 51: 570-579;
Ward-Paige et al, 2005: MEPS 296: 155?163).

In fact, the real question is: why coral reefs? Why are coral reefs the
only ecosystem on the planet for which the impact of nutrient excess
has to be proven again and again, seemingly in the face of implacable
opposition? I stray from the focus of this posting, but I fear the
answer may lie in the evil triumvirate of careers, CYA, and cash. Reef
managers are reluctant to admit that the decline is due to local
sources-it is much easier to blame ?global change?, the control of
which is outside their job description. In addition, as some posters
have alluded, there is always a market for scientists who will say a
given coastal development (golf course, marina, whatever) will have no
impact because, after all, nutrients are unimportant.

Back to The Destroyer. Christine Ward-Paige and I devised a
quick-and-dirty scheme for FMRI by which amounts of C. delitrix could
be estimated. Nothing special, a diver simply swims a transect line
with a quadrat frame (25x25cm divided into 5x5cm squares works well),
estimating area of delitirix. This takes next to no time. The problem
with converting these measures to estimates of framework destruction is
that colonies of delitrix are not two-dimensional. It frequently drives
straight into the heart of the coral. Rose and Risk gives some idea of
the variance involved in estimating rates from areas-but areas are a
start, and it?s easy. Delitrix does not occur in the Indo-Pacific.

The Indo-Pacific is easier, and more difficult. Easier surveying,
harder identifying.

There is a circum-tropical sponge that I have seen in every reef
province I have dived. (Many years ago I published a wee paper pointing
out that the boring sponge fauna really is worldwide, unlike the
corals: the sponges are older, and what we see now is the remnant of a
Pan-Tethyan distribution). It?s the same damn critter everywhere, with
regional differences, but has been given a plethora of names: Cliona
caribbaea, viridis, orientalis, langae, yadda yaddae. Christine has
listed some of the synonyms.

This sponge excavates down about 1cm, then spreads out over the surface
removing about 50% of the substrate. It is therefore a two-dimensional
critter, and area equals destruction. Previous studies (eg Acker and
Risk, Caribbean; Bergman and Risk, GBR-on the GBR, it is the single
most abundant benthic species on bommy walls) have shown it capable of
removing material at 15kg/m2/year, or about twice the rate at which
present-day Caribbean reefs calcify. So monitoring this guy with
quadrats makes good sense.

It?s harder to identify than delitrix, at least until you get your eye
in. At first, it looks like an algal scum-the sponge has zooxanthellae,
so it?s brown/olive in colour. If you look closely, however, you will
see the oscula on the surface. These tend to be about 2mm diam, often
raised a bit...sometimes, as I saw in the Banda Islands, oscular rims
are outlined in bright green for some unknown poriferan reason. Maybe
SpongeBob knows.

So there it is. Delitrix in the Caribbean, Cliona multiname everywhere.
Enough. I?ve written papers that took less time than this posting-now I
need to get in some firewood.


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

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