[Coral-List] Mucus Production
Jim.Hendee at noaa.gov
Fri Oct 1 11:46:43 EDT 2004
I'm forwarding this for James Cervino, who has had a difficult time
posting the message through the listserver for some reason. Please
write to him or Tom Goreau with any comments and do not reply to me
(because I'm clueless on mucus). Thanks...Jim
Subject: Mucus discussion
From: James M Cervino <cnidaria at earthlink.net>
Date: Fri, 1 Oct 2004 09:04:52 -0400
To: coral-list at coral.aoml.noaa.gov
Tom Goreau asked me to submit this on the list as many people were
having problems with their search and getting on the GCRA web-site.
CORAL BLEACHING AND MUCUS RELEASE
NOTE: The following letter and response clarify the important role of
mucus in coral reef ecosystems presented in a recent paper by Wild et
al., and the effects of bleaching on them. They were submitted to
NATURE, which declined to publish them as "not being of sufficient
interest to the scientific community". As we disagree, in cooperation
with Dr. Wild and colleagues we are circulating the exchange to those
concerned about the implications for reef ecology. Thanks GCRA.
LETTER TO NATURE BY:
Thomas J. Goreau, Global Coral Reef Alliance, 37 Pleasant Street,
Cambridge MA 02139, 617-864-4226, goreau at bestweb.net
James Cervino, Department of Marine Science, University of South
Carolina, Columbia, SC 29073, 917-620-5287, cnidaria at earhlink.net
Raymond Hayes, College of Medicine, Howard University, Washington DC
301-585-5892, rhayes at Howard.edu
Wild et al. (Nature 428:66-70; 2004) show that coral mucus functions as
an energy carrier and particle trap within a tropical reef ecosystem and
demonstrate its important role in nutrient recycling. However, several
important points need further explanation and suggest that these
measurements may be atypical.
First, while some corals may constantly secrete mucus, few do so
at a constant rate, as stated. Copious mucus release is the first
visible sign of a generalized response to environmental stress (Helgol.
Meeresunters. 37: 113-137, 1984; Revista de Biología Tropical
(5):173-185, 1998), including sediment and freshwater (Science 145:
383-386, 1964), aerial exposure (which was used to determine mean mucus
production in the paper), cyanide exposure (Mar Poll Bul 46: 573-586,
2003), and coral bleaching (Sci. Rep. Gr. Barrier Reef Exped. 1928-1929
1931 ; Science 145: 383-386, 1964; Coral Reefs vol. 12 pp. 1-17,
Secondly, all the photographs, including the cover, show corals that are
clearly bleaching. However, the authors do not note (either in the text
or in Table 1) that the corals were bleached, nor do they mention that
most of this work was conducted during the most intense coral reef
bleaching event to have ever taken place on the Great Barrier Reef
(GBRMPA, 2002). Corals that are thermally bleached have expelled their
symbiotic zooxanthellae and have produced copious amounts of mucus,
which would explain the high levels of mucus release that the authors
observed. Increased mucus release occurs before corals visibly pale.
This would also explain the dense mucus "floc", which is typical of
severe stress, mass bleaching, or mass spawning events, which may also
have been prematurely triggered by severe thermal stress.
Thirdly, bleached corals are deficient in the chemical
precursors normally released by zooxanthellae and used for coral mucus
synthesis, so the biochemical composition of their mucus abnormal (Proc
R Soc London Ser B 177: 237-250, 1971; Limnol Ocean,19; (5)
810-814,1974; Mar Biol. 79: 27-38,1984). This alters the microbial
flora living on it (Proc Amlc 27:26-34).
In summary, we believe that the quantity and quality of coral mucus
release and its role as a microbial substrate is highly variable in
space and time, and fluctuates with the varying stresses corals are
exposed to. Therefore, further research is warranted to more fully
quantify the importance of mucus cycling that Wild et al. demonstrate.
Battey, J.F., and J.S., Patton. (1984). A reevaluation of the role of
glycerol in carbon translocation in zooxanthellae-coelenterate
symbiosis. Mar Biol. 79: 27-38.
Benson A.A., L., Muscatine (1974). Wax in coral mucus: Energy transfer
from corals to reef fishes. Limnology Oceanography, vol 19; (5) 810-814.
Cervino J.M., R.L. Hayes, M. Honovich, T.J.,Goreau S. Jones, P.J. Rubec
(2003). Changes In Zooxanthellae Density, Morphology, and Mitotic
Index in Hermatypic Corals and Anemones Exposed to Cyanide. Mar
Poll Bul 46: 573-586.
Glynn P.W., (1993). Coral reef bleaching-ecological perspectives. Coral
Reefs vol. 12 pp. 1-17.
Goreau T.F., (1964). Mass expulsion of zooxanthellae from Jamaican reef
communities after Hurricane Flora. Science 145: 383-386.
Great Barrier Reef Marine Park Authority,(2002). Coral Bleaching
Hayes, R. L. and N. I. Goreau, (1998). "The significance of emerging
diseases in the tropical coral reef ecosystem." Revista de Biología
Tropical 46(Supplement 5):173-185.
Peters, E., (1984). "A survey of cellular reactions to environmental
stress and disease in Caribbean scleractinian corals." Helgol.
Meeresunters. 37: 113-137.
Ritchie, K.B., A. Jindal, R. L. Hayes, T. J. Goreau and G.W. Smith,
(1994). Bacterial ecology of selected corals following the 1994 south
central Pacific bleaching event. Proc AMLC 27: 26-34.
Trench, R. K., (1971). The physiology and biochemistry of zooxanthellae
symbiotic with marine coelenterates. 11. Liberation of fixed 14C by
zooxanthellae in vitro . Proc R Soc London Ser B 177: 237-250.
Yonge, C.M. and A.G. Nicholls, (1931). Studies on the physiology of
corals. IV The structure, distribution and physiology of the
zooxanthellae. Sci. Rep. Gr. Barrier Reef Exped. 1928-1929 1, 135-176.
RESPONSE BY DR. CHRISTIAN WILD
Dear Madam or Sir,
We were notified by Goreau, Cervino and Hayes that they have submitted a
note to Nature addressing our Nature letter "Coral mucus functions as an
energy carrier and nutrient trap in the reef ecosystem" (Nature 428:
66-70, 2004). Goreau et al. raised some interesting points, however, we
disagree with some of their interpretations of our work. Below, please
find our reply to the comments of Goreau and colleagues.
Christian Wild and coauthors
Response to the comments of Goreau, Cervino and Hayes to our article
"Coral mucus functions as an energy carrier and nutrient trap in the
reef ecosystem (Nature 428: 66-70, 2004). Each citation from the letter
by Goreau et al. (in italics) is followed by our reply to the respective
comment. Citations in sequence as stated in the letter by Goreau et al.
Goreau et al.: First, while many corals do constantly secrete mucus, few
at a constant rate, as stated.
We do say that corals constantly have to secrete mucus to protect
themselves against fouling, desiccation and sedimentation (page 66,
first paragraph, ref. 5-7), but we state clearly that this release is
not constant as evidenced by our experiments with air exposure stress
(see page 66, last paragraph and page 67, first sentence).
Goreau et al. : Greatly elevated mucus release is the first visible sign
of a generalized response to almost all stresses (Helgol. Meeresunters.
37: 113-137, 1984; Revista de Biología Tropical (5):173-185, 1998),
including sediment and freshwater (Science 145:> 383-386, 1964), aerial
exposure (which was used to determine mean mucus production in the
We did not use our container experiments with air exposure to "determine
mean mucus production" as stated by Goreau et al. This is clearly stated
in the text: on page 66, last paragraph, we describe the mucus
production of submersed corals and on page 67, first paragraph we show
the results of our container incubations with air exposure. Also, the
mucus release rates that we used for our budget calculations (summarised
in figure 3) are only based on the beaker incubations to stay
conservative (this is also stated in the article text on page 68, last
paragraph and page 69, first paragraph). Two independent beaker
incubation experiments were conducted, one in 2001 and the other in 2002
(both in the Australian summer). For these experiments and the
compositional mucus analyses only unbleached corals were used, for which
we have photographic proofs. The results of the experiments in 2001 and
2002 are very similar and also comparable to the range of release rates
observed by other authors at other times and locations (see Table 1).
We certainly agree that mucus release fluctuates because of a range of
environmental stress factors like high temperature, salinity change,
pollution (Loya & Rinkevich 1980, Kato 1987), turbidity (Rublee et al.
1980, Telesnicki & Goldberg 1995) and sedimentation (Hubbard & Pocock
1972, Schuhmacher 1977). Our container experiments including air
exposure as environmental stress factor for the incubated corals show
higher mucus release rates than the beaker incubations (see Table 1
below; method, see ref. 26 in Nature letter). A new publication (Wild et
al., submitted to MEPS: Quantitative and qualitative analyses of coral
mucus release and its influence on nutrient fluxes in carbonate sands)
addresses this subject in detail.
Goreau et al. : Secondly, all the photographs, including the cover, show
corals that are clearly bleached; however, the authors do not note
(either in the text or in Table 1) that the corals are bleached, nor do
they mention that most of this work was conducted during the most
intense bleaching event to have ever taken place on the (GBRMPA,2002).
Our study is based on work conducted in the years 2001 and 2002 (in
approximately equal amounts), of which only year 2002 was a year of
extensive bleaching events in the Great Barrier Reef. During our
expedition to Heron Island in January 2002, however, we could only
observe minor bleaching, probably because we did our investigations at
the very beginning of this bleaching period. The Great Barrier Reef
Marine Park Authority reports that in January 2002 the first signs of
bleaching were recorded on many locations within the Great Barrier Reef
(see more details at the website
and Heron Island is located at the southern end of the Great Barrier
Reef where temperatures are usually lower.
At Heron Island we recorded in 2002 that some of the corals were
partially bleached like it is seen on the Nature cover. The figure on
the cover page is the same at in Fig. 1a, but enlarged and enhanced in
brightness. The water cover in Fig. 1c, from our point of view, does not
permit an assessment whether any of the depicted corals were bleached,
thus, there is just one photograph of corals displayed in the whole
letter. It is therefore disproportionate to write, "all the photographs
show corals that are clearly bleached". We submitted the photograph to
Nature because of the good quality and also because the mucus strings
are very clearly visible. However, we have a range of other photographs
showing unbleached corals with similar mucus strings attached. These
photographs were taken at the same time and can be provided upon
request. We observed mucus strings on unbleached corals frequently also
at other locations than the GBR. One of those pictures was made in the
Northern Red Sea and can be seen on the Science Magazine website at the
following link: http://sciencenow.sciencemag.org/cgi/content/full/2004/305/1
Goreau et al. : Corals that are thermally bleaching expel their
symbiotic zooxanthellae and produce copious amounts of mucus, which
would explain the high levels of mucus production that the authors
observed. This would also explain the dense mucus "floc", which is
typical of severe stress, mass bleaching, or mass spawning events (which
may have been prematurely triggered by severe thermal stress)
Bleaching may enhance mucus production; however, bleaching is not
necessary to induce massive mucus release from corals as can easily be
demonstrated by exposing healthy corals to air. Our container
experiments quantified the latter process. Massive mucus release as a
consequence of air exposure is also observed in years without any coral
bleaching and was also reported from other reef environments in
Australia, Madagaskar, the Red Sea and Hawaii (Krupp 1984, Romaine et
al. 1997). Subsequent formation of floating mucus aggregations was also
described for reef flats in Hawaii (Krupp 1984), thus this phenomenon is
neither site-specific, nor necessarily connected to coral bleaching or
atypical as stated by Goreau and colleagues.
Goreau et al.: Thirdly, bleached corals are deficient in the chemical
precursors normally released by zooxanthellae and used for coral mucus
synthesis, so the biochemical composition of their mucus changes.
The detailed mucus composition results are based on mucus samples from
unbleached corals and collected in 2001 and 2002. Any possible bleaching
effects do therefore not affect the samples. However, we agree that
stress and bleaching may change the composition of coral mucus.
Goreau et al.: In summary, we believe that the quantity and quality of
mucus as a microbial substrate is highly variable in space and time, and
fluctuates with the varying stresses corals are exposed to. Therefore,
further research is warranted to more fully quantify the importance of
mucus cycling that Wild et al. demonstrate.
Our work focusing on one genus of corals (Acropora) only cannot claim to
be sufficient to quantify mucus release and mucus composition in corals
or the variability of mucus quantity and quality. The aim of our study
was to demonstrate the recycling of coral mucus in the reef ecosystem
and to show that the mucus, which is a dominant fraction of particulate
organic matter in coral reefs (Johannes 1967, Marshall 1968), is a
carrier of nutrients and efficient particle trap. Bleaching events may
enhance this recycling loop; however, the mechanisms described in our
letter to Nature (mucus dissolution, particle trapping, sedimentation,
sedimentary filtration and degradation) are independent of such stress
Table 1. Mucus release as carbon in comparison to other studies
(modified after Wild et al., submitted to MEPS). The container
experiment included exposure to air resulting in elevated mucus release
rates. Numbers in brackets are standard deviations.
Study site Species Mucus C release (mg/m_ coral surface/h) N
Heron Island (2002) Acropora millepora 117 (79) 8
container Wild et al. (2004)
Heron Island (2002) Acropora millepora 10 (5) 5 beaker
Wild et al. (2004)
Heron Island (2001) Acropora aspera 7 (3) 8 beaker Wild et
Eilat Acropora variabilis 1.4-4.2 perspex chamber Crossland
Eilat Stlyphora pistillata 2.7-4.0 perspex chamber
Jamaica Acropora palmata 18 3 Stirred chamber Means &
Bight of Piran Cladocora cespitosa 6 12 beaker
Herndl & Velimirov (1986)
Hubbard JAE, Pocock YP (1972) Sediment-rejection by recent scleractinian
corals: a key to palaeo-environmental reconstruction. Geol Rundschau
Johannes R (1967) Ecology of organic aggregates in the vicinity of a
coral reef. Limnol Oceanogr 12:189-195
Kato M (1987) Mucus-sheet formation and discoloration in the
reef-building coral, Porites cylindrica : Effects of altered salinity
and temperature. Galaxea 6:1-16
Krupp DA (1984) Mucus production by corals exposed during an extreme low
tide. Pac Sci 38:1-11
Loya Y, Rinkevich B (1980) Effects of oil pollution on coral reef
communities. Mar Ecol Prog Ser 3:167-180
Marshall M (1968) Observations on organic aggregates in the vicinity of
coral reefs. Mar Biol 2:50-55
Romaine S, Tambutte E, Allemand D, Gattuso JP (1997) Photosynthesis,
respiration and calcification of a zooxanthellate scleractinian coral
under submerged and exposed conditions. Mar. Biol. 129:175-182
Rublee P, Lasker H, Gottfried M, Roman M (1980) Production and bacterial
colonization of mucus from the soft coral Briarium asbestinum. Bull Mar
Schuhmacher H (1977) Ability of fungiid corals to overcome
sedimentation. In: Proceedings of the Third International Coral Reef
Symposium, Miami, Florida, p 503-509
Telesnicki G, Goldberg W (1995) Effects of turbidity on the
photosynthesis and respiration of 2 South Florida reef coral species.
Bull Mar Sci 57:527-539
James M. Cervino, Ph.D. Candidate
Invertebrate Physiology & Pathology
Marine Sciences Department
University of South Carolina
cnidaria at earthlink.net
More information about the Coral-List