[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
interested.
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
turn.
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
responses.
Christine
Dr. Christine Schoenberg
Carl von Ossietzky Universitaet Oldenburg
Fakultaet 5
Institut fuer Biologie und Umweltwissenschaften
AG Zoosystematik und Morphologie
26111 Oldenburg
Germany
ph +49 (0)441 798 3611
fax +49 (0)441 798 3250
(alternative email: christineaway at gmx.net )
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