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S. Calm et al. /Science of the Total Environment 165 (1995) 23-31 27

crocoleus lyngbyaceus) and by Ectocarpaceae Scuba diving observations, carried out below
(Acinetosporu crinita), forming thick mucillagi- the thermocline layer (located at a depth of 15 ml
neous bundles (Giaccone, 1992). at the beginning of July, revealed a dense
brownish cover laying on the sea bottom and
3.3. Sicilian Channel wrapping the benthic communities (Fig. 5).
The conditions in this area during the summer Microscopic examinations showed a threadlike
of 1991 were obtained merely by collecting infor- alga without any evident gelatinous sheath and
mation from scuba diving clubs, who supplied with a few epiphytic diatoms (Licmophora spp.)
photographic documentation, and from local growing.
fishermen. At the end of July, the Ectocarpaceae popula-
Poszifoniu oceanicu meadows and the biocoeno- tion considerably decreased and was nearly com-
sis colonizing the eulittoral zone and the rocky pletely replaced by Cladophoraceae (Cludophoru
banks offshore, were massively covered by mucil- sp.>. This second filamentous alga, having thick
lagineous bundles. The analysis of the pho- gelatinous sheaths, formed large bundles laying
tographs taken by scuba divers led us to suggest on the sea bottom like cotton wool (Fig. 6). The
that the organisms involved were principally rep- sheaths, especially in the older organisms, were
resented by Ectocarpaceae. densely colonized by diatoms, mainly represented
In 1992, at the end of February, dense pelagic by Licmophora sp., and by the red alga Audou-
mucus aggregates were observed at the Isola delle niella sp. At the same time decomposing Ecto-
Femmine station. The survey carried out showed carpaceae accumulated into the depressions of
the occurrence of a bloom of comb jellies the rocky sea ground were observed.
(Ctenophoru) forming long mucus strings free During August, the phenomenon gradually de-
floating in the water column and on the surface. creased and, at the end of the month, the meta-
This phenomenon vanished in one week. phytic communities had almost completely disap-
At the end of June, a massive growth of meta- peared.
phytic Ectocarpaceae was observed on the sea During all of the summer of 1992, Secchi disk
bottom. transparency depth showed high values (> 25 m)

Fig. 5. Metaphytic Ectocarpaceae laying on horny coral during the summer of 1992.