[Coral-List] New paper on coral reef sponge cell kinetics

[Jasper de Goeij]

Dear all,

I'm happy to announce a new paper by our group, titled "Cell kinetics
of the marine sponge Halisarca caerulea reveal rapid cell turnover and
shedding", published in The Journal of Experimental Biology. I'm also
happy to inform you that the paper is featured in the "Inside JEB"
section and will be highlighted in Nature tomorrow.

Although the subject of this paper is not on corals, it has
implications on the ecological function of sponges, being filter
feeding organisms, on the carbon-(re)cycling on the reef.  We
estimated in earlier work that coral cavities (the cryptic habitat) is
taking up huge amounts of organic carbon, primarily in the form of
dissolved organic carbon. Sponges, living inside those cavities are
responsible for this carbon uptake. The coral reef cavity sponge
Halisarca caerulea is taking up about two-thirds of its biomass per
day in terms of organic carbon intake (>90% as DOC). More than half
(appr. 60%) of that daily intake is assimilated. Therefore, this
sponge should double in biomass every three days on average. However,
it does not. Sponges are considered slow growers, and also this sponge
showed a growth rate of almost zero. So where is all this carbon going
to? We found that the sponge shows a very fast turnover of cells,
mainly choanocytes. The cell cycle we measured is the fasted every
measured in a multicellular organism (appr. 5.4 hours). The
choanocytes are proliferating as a single cell population and 'old'
cells are being expelled in the canals leading to the outflow
openings, just like in the epithelium of the mammalian
gastro-intestinal tract. We hypothesize that sponges show this cell
kinetics because of their environment. Competition for space on the
coral reef and especially in coral cavities is very high. Moreover,
they live in the aquatic equivalent of a desert, therefore need to
filter enormous volumes of water daily. The chances of physical or
chemical damage of the uptake (filter) system is potentially high. To
prevent damage, the sponge 'renews' its filter system constantly. The
life strategy of this sponge is not to grow large, but to grow old. We
calculated that the costs for cell proliferation are in the same order
of magnitude as the fluxes of organic carbon into the sponge, which
corroborates with our recent high DOM-fluxes. We believe this paper
sheds new light on the growth characteristics of sponges. By turning
dissolved organic matter, which can hardly be taken up by most
organisms on the reef, into particles, which can be used by most reef
dwellers, sponges are playing an important role in the cycling of
energy within the coral reef ecosystem. In our next paper, we hope to
present you detailed energy budgets, showing this ecological role of
sponges within the coral reef.

Cell kinetics of the marine sponge Halisarca caerulea reveal rapid
cell turnover and shedding (2009)
J. M. De Goeij, A. De Kluijver, F. C. Van Duyl, J. Vacelet, R. H.
Wijffels, A. F. P. M. De Goeij, J. P. M. Cleutjens, and B. Schutte
J Exp Biol 212: 3892-3900

If you are interested (receiving a PDF of the paper), have questions
or comments, please do not hesitate to contact me.

All the best,

Jasper.

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Dr. Ir. J.M. de Goeij
Porifarma BV, CEO
Poelbos 3
6718 HT Ede
The Netherlands
Tel. +31 6 52471433
www.porifarma.com
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