Page 8 - Observations_1995

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

c
5
E
a

Chl a IrOn) P-PO4 N-NH4 N-NO2 N-NO3
Fig. 10. Mean chlorophyll a, total phosphorus and nutrient concentrations during the spring and summer of 1992 at the Sciacca
station.

ible nowadays to explain the mechanisms underly- Messina Strait effects, respectively, were not in-
ing the peculiar phenomenon of amorphous ag- volved by mucus aggregate development.
gregates in the summer of 1991. An additional nutrient enrichment of the
We suppose that amorphous mucus aggregates Tyrrherian sea due to welling-up phenomena, sti-
had a pelagic origin like those reported in the mulating phytoplanktonic growth, as suggested by
Adriatic Sea (Stachowitch et al., 1990). Their high satellite images (Fresi, E., pers. commun.), may
sinking rates (Alldredge and Silver, 1988) cause a be proposed.
deposition on the sea bottom commonly colo- As a whole, the causes and the origins concern-
nized in the summer season by metaphytic Ecto- ing mucus aggregates should be investigated with
carpaceae. regard to the entire western Mediterranean basin.
Sunken mucus aggregates could represent a A general investigation, involving all the different
coagulation inoculum site for mucillagineous research groups working in the marine biology
products of benthic organisms, together forming a field, must be planned in order to provide a real
thicker layer and a peculiar habitat. In these understanding of the mechanisms underlying the
microcosms the activity of autotrophic and het- phenomenon of mucus aggregates.
erotrophic organisms can be closely linked,
thereby providing mutual benefits. 5. Summary
Riebesell (1992) reports that high phytoplank-
ton cell concentrations and low wind-induced Mucus aggregates, covering a large area of the
mixing of the water column have to occur to sea bottom, were observed along Sicilian coasts
favour the formation of large macroflocs and during the summer of 1991. This phenomenon
stringers. caused, especially along the Tyrrherian coast, a
Thus, the development of mucus aggregates cessation of fishing activities because of the clog-
was probably supported, during the summer of ging of nets.
1991, by the low hydrodynamism in the T)rrhe- The phenomenon showed different develop-
nian sea due to the particular climatic conditions. ment patterns along the various Sicilian coasts
On the other hand, the Sicilian Channel and the subjected to different hydrodynamics. Amorphous
Jonian Sea, subjected to Atlantic currents and to mucus aggregates, showing a similar behaviour