Page 4 - Observations_1995

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

Fig. 4. The cobweb-like covering which occurred during the summer of 1991.

analogy. The amorphous aggregates were gener- In September 1991, with the occurrence of
ally seen inside a large amount of detritus and sea-storms, all of the mucus aggregates com-
microalgae. The microalgal component of the up- pletely disappeared. Subsequent observations did
per layer of benthic aggregates was mainly repre- not show any particular stress or signs of decay in
sented by a diversified community of diatoms. the benthic biocoenosis. Only the horny corals
The epipelic and planktonic Nitzschia closterium manifested some damage to the coenosarc.
was generally the dominant species, but benthic What we have described probably is the last
diatoms, such as Licmophora spp., Mastogloia spp. stage of a phenomenon originating some months
and Navicula spp. were also well represented in before our observations. Moreover, cellular densi-
the samples. Moreover, among the lower layer of ties within the aggregates were too low to justify
benthic mucus aggregates, which was more such a large production of mucilage, which could
strongly attached to horny corals and Cystoseira, indicate a temporal and spatial shift between the
filamentous Ectocarpaceae (Acinetospora crinita) phytoplanktonic growth and the appearance of
were present. amorphous mucus aggregates floating in the wa-
The planktonic mucus aggregates evidenced a ter column and laying on the sea bottom. Inciden-
lower detrital component and an extremely diver- tally, a neustonic bloom, which occurred in
sified assemblage of included planktonic organ- November 1990 and was supported by the growth
isms. The algal community was particularly domi- of the small colonial planktonic diatom Cyclotella
nated by diatoms (Nitzschia seriata, Rhizosolenia cf. choctawhatcheana, was recorded spreading for
spp.) and dinoflagellates (Ceratium SPP.7 several hundreds of kilometers offshore from the
Gonyaulax spp., Protoperidinium spp.). north-western Sicilian coasts from Palermo to
Neustonic aggregates also showed a low detrital Mazara de1 Vallo.
component and included planktonic organisms. In
the latter case, Pyramimonas sp. (Micromona- 3.2. Jonian coast
dophyceae), Chaetoceros spp. (Bacillariophyceae) On the sea bottom off the Sicilian eastern coast
and Gymnodinium sp. (Dinophyceae) were the there was a massive development of benthic al-
dominant taxa. gae, mostly represented by Oscillatoriaceae (Mi-