sick sea fans

[Katharina Fabricius]

Dear Listers,

this is getting interesting:

I surveyed the octocorals of the reefs in Hong Kong waters in November last
year, together with Denise McCorry, Yehuda Benayahu, and Brian Morton. In
some areas, disease and mortality of sea fans were as high as ~80%, in the
"best" areas it was around ~20%. A large proportion of colonies suffered
partial mortality (live tissue occurred on a proportion of  branch
segments, while the remaining branch segments were dead or overgrown with
algae). The area is very turbid and highly polluted (eg, see the extensive
literature on the state of the reefs of Hong Kong by Brian Morton). All 13
genera recorded of gorgonians were azooxanthellate taxa, hardly any
zooxanthellate soft corals and no zooxanthellate sea fans occured
throughout the 42 sites surveyed . 

In contrast, I have also surveyed > 1300 sites on the Great Barrier Reef
(GBR) for octocoral community composition & taxonomic inventories, and
diseased sea fans are exceptionally rare throughout the GBR. Furthermore, I
have surveyed the octocorals on > 160 sites on the Florida Keys in 1991
together with Ken Sebens, and we did not notice unusual levels of diseased
gorgonians then. 

I suspected for a long time that many sea fans are pretty sensitive
critters, and thanks to this CHAMP list it now appears to become more
evident that the health of sea fans may be some sort of indicator for
deteriorating water quality. It helps is that the central axis of many
gorgonian taxa  doesn't decompose for several months after death. I would
be keen to hear records from more parts of the world to see where it
happens and where not. I will certainly keep a closer look-out for diseased
gorgonians in future when visiting areas of the GBR which are exposed to
agricultural run-off.

Katharina Fabricius

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Dr. Katharina Fabricius
Research Scientist
Australian Institute of Marine Science
PMB 3, Townsville Qld 4810, Australia

Fax    	+61 - 7 - 4772 5852
Phone 	+61 - 7 - 4753 4412  or 4758 1979
email k.fabricius at email.aims.gov.au

http://www.aims.gov.au
http://www.reef.crc.org.au