[Coral-List] more thoughts on (sponge) bioerosion

Christine Schoenberg christine.schoenberg at uni-oldenburg.de
Tue Oct 24 07:35:58 EDT 2006

Dear Listers,

I had a few busy days, but I still meant to throw some thoughts into the 
arena of the bioerosion discussion. My background are mainly bioeroding 
sponges, so my ideas mainly refer to them. That does not mean that I 
would neglect any of the other bioeroders, but there are other experts 
to touch on that. If you don't like these sponges, you can stop reading 
now, it will be a long mail.

I very much appreciate Mike's comments. They clearly show that he's been 
in the field a lot and noted some of the trends and changes just by 
being there and keeping his eyes open. I think anyone can recognise such 
changes nowadays as long as you are regularly out in the water over a 
longer period of time. And I think once changes are easy to recognise 
it's big enough that it deserves our attention.

A few words of caution: Species recognition in bioeroding sponges is a 
bitch. I tried to hint at it with my earlier mail, but Mike has promptly 
declared most of the important species as synonymous (thanks 
Mike... ;-)  ). They are not. OK, even us specialists are not always 
sure how to ID the sponges in the field, but we have acquired fairly 
good ideas about tissue samples and spicule preparations. There are also 
some molecular results now available that divide the Cliona viridis 
complex into separate species (i.e. the brown ones). The Cliona celata 
complex (the yellow ones) and others will follow suit. That doesn't 
necessarily match our abilities to split the species on the 
morphological level as well, and not even talking of how you know what 
you are looking at in the field. It makes monitoring very tricky and it 
becomes almost impossible to keep up with name changes, taxonomic 
revisions and synonymies or homonymies. As I said: it's a real bitch. 
But never mind, we can start small and go from there. It is less 
important at the moment to be accurate about names than to show that the 
sponges are increasing in abundance.

I did receive interested feedback after my last posting, i.e. people who 
would like to join a simple monitoring approach. I propose to conduct a 
regular study at various sites in the world and try to keep it going for 
a while. For now the aim would be to pick up possible trends in 
bioeroding sponge abundances and how that would impact on the carbonate 
balance. This needs to be large-scale, long-term and as comparable 
between sites as possible, so hopefully we can do some stats on results. 
As species recognition is difficult and estimating the biomass is 
another conundrum, I would say we should keep it to 'beta stage' growth 
form sponges only, which there are usually only very few species per 
site. They are the bad guys, they grow fast, they attack live coral and 
they are generally very successful. Some of them has been recognised as 
good biomonitors. Beta stage means: a bioeroding sponge that is evenly 
penetrating the substrate instead of making the Swiss-cheese or the 
single-cavity pattern, eroding maybe to 1 to few cm depth, and it has 
_continuous_ tissue covering the substrate surface. They usually have 
brown or orange colours. I think the easiest would be line-intercept 
transects, i.e. running out a measure tape and noting the cms of the 
tape that cross over such a sponge. The sponge occurrence needs to be 
normalised to 'substrate available', which is coral, carbonate blocks 
etc. in the case of beta sponges, I think we can ignore mollusc shells, 
rubble and probably branching coral as well. You need to note type of 
substrate, ideally to coral genus. Wherever such sponges sit right next 
to live coral tissue it should be noted. You should try to find out how 
many different species there are at your site and take 3-5 reference 
samples per species for later ID, this includes good underwater photos 
with scale and before you start prodding the sponge, and info about 
date, site, depth, substrate. Sponges should never be pickled in 
formaline, but either frozen -20C or preserved in high-percentage 
ethanol. 70% will do, but higher % is better. You need to estimate the 
average depth these critters erode to at your site, e.g. by taking cores 
with an air-driven drill. This needs to be a fairly large sample size of 
at least 10 cores, as erosion depth varies with substrate and turbidity. 
Depth of occurrence varied with turbidity for the brown (zooxanthellate) 
sponges. I think you should find the area of the highest abundance of a 
given sponge and then run 5 randomly placed transects in parallel to 
that zone. On the coastal GBR that would be the reef crest or shallow 
reef areas, mainly in massive Porites, the sponge there would be Cliona 
orientalis. I am not quite sure how long the transects will have to be, 
let's start with 20m. I don't know exactly what the respective 
conditions would be at other sites, it would be great if you could send 
me some data of pilot studies, so we could come up with a 'normalised' 
approach everybody can use. This should be conducted 2x per year, in 
summer and in winter. Hm, that's what I can think off right now. Does 
that sound feasible? Once I get back some feedback we can refine this 
approach and forward it to monitoring people and others who are 

Some other thoughts:
Maybe increased nutrients are not causing increased abundance of 
bioeroding sponges, maybe we need to look into what kinds of food. Which 
may explain why some reef areas have much erosion and others only 
little, even though both may be impacted by nutrient sources.
Bioeroding sponges appear to be strong in terms of changing 
environments. Just think about it: they are sitting inside of some nice, 
sheltering material into which they can withdraw to some degree if 
things on the surface become dodgy. They would not be much affected by 
climate change stresses: The substrate provides shading, filter feeding 
may provide some cooling with the water current (?), and there are other 
mechanisms that play a role as well, cell migration, pigments, you name 
it (Schoenberg & Suwa, submitted). Especially the big competitive 
bioeroding sponges (the bad betas) are strong stuff. Think about what 
will happen if corals continue to die, thus creating ideal settling 
ground for bioeroders (not only sponges) that do not continue to die in 
There was a discussion about how much sponges contribute to chemical and 
mechanical bioerosion. 2-3% in Pione lampa are supposed to be chemically 
dissolved, the rest is going out with the feeding currents, joining the 
rest of the reefal sediments as silt-sized lentil-shaped chips (Ruetzler 
K & Rieger G 1973. Sponge burrowing: Fine structure of Cliona lampa 
penetrating calcareous substrata. Marine Biology 21: 144-162. See also 
the review by Pomponi SA 1980. Cytological mechanisms of calcium 
carbonate excavation by boring sponges. In. Rev. Cytol. 65: 301-319.). 
But since the 1980s nobody has looked into that stuff anymore, maybe 
it's about time for a retake with modern technology.
We know so little about bioeroders. We know about their taxonomy if we 
are lucky, we have some bioerosion rates and distribution patterns. But 
how do they interact with their hosts or other organisms nearby. How do 
they reproduce? How will they be affected by changing environments? We 
have some exciting results in front of us, I am very sure if it.

Sorry for the lengthy 'boring' comments. Looking forward to your 


Dr. Christine Schoenberg

Carl von Ossietzky Universitaet Oldenburg
Fakultaet 5
Institut fuer Biologie und Umweltwissenschaften
AG Zoosystematik und Morphologie
26111 Oldenburg
ph +49 (0)441 798 3611
fax +49 (0)441 798 3250

(alternative email:  christineaway at gmx.net )

More information about the Coral-List mailing list