• Partial view of Lake Faro from land

Alessandro Saccà

Microbial Plankton Ecologist

Faro Lake on Earth Icon

My most interesting studies were conducted on Faro Lake, a peculiar coastal basin located on the north-eastern tip of the Sicily Island (Central Mediterranean). Faro Lake, together with Ganzirri Lake, is part of the Peloro Cape Lagoon System, an oriented natural reserve at only 9 Km from the centre city of Messina.

The two lakes most probably originated between 3000 and 2500 b.C. from a previously existing coastal lagoon. This, in turn, derived from fluvial detritus that was transported by marine currents until forming sandy dunes which enclosed part of the sea at the mouth of the Straits of Messina. The coastal lagoon later broke up into four smaller lakes, two of which eventually merged to form Ganzirri lake, another one was artificially drained about two centuries ago, whereas Faro Lake underwent only minor changes.

Faro Lake (38° 16’ N, 15° 38’ E) features a surface area of about 263,600 m², and a greater diameter of 665 m. Its estimated water volume is of about 2.500.000 m3. It is connected via a shallow channel to the Straits of Messina, a stable upwelling system driven by the strong tidal currents flowing between the Ionian and the Tyrrhenian seas (Brandt et al. 1997), which strongly influences the lake ecology (Saccà et al. 2008). Another channel connects it to Ganzirri Lake.

While Ganzirri Lake is a relatively shallow coastal basin (not more than 6.5 m deep), Faro Lake features a steep sloping bottom that declines to a central region reaching a maximum depth of 30 m. Considering the correspondence of the shorelines of the lake with half graben faults, a tectonic event is the most likely explanation for the remarkable depth of this basin.

The most remarkable feature of FaroLake is the persistent physical and chemical stratification of its water column. Particularly, it is possible to distinguish two main zones: a mixed upper layer, defined as the mixolimnion, and a stagnant lower layer, defined as the monimolimnion. A transition zone also exists between them, named the chemocline.

While the mixolimnion is well oxygenated, chiefly due to advection processes, the monimolimnion is anoxic and usually characterized by a vertical gradient of hydrogen sulfide (H2S) concentration, reaching a maximum at the water/sediment interface.

The high stability of the water column in summer, along with the increased light availability, triggers regular blooms of photosynthetic sulfur bacteria in the upper monimolimnion (Trüper and Genovese 1968Sorokin and Donato 1975; Saccà et al. 2009).

For its persistent water column stratification, FaroLake ranks among meromictic basins. These have long attracted scientific interest because of their importance in biogeochemical processes. In fact, they are inhabited by communities of free-living prokaryotes which are able to exploit the wealth of ecological niches existing along the chemical gradients of the water column:

Anoxic waters host populations of fermenting, sulfate reducing, denitrifying and methanogenic Bacteria or Archaea, each thriving at different depths according to local redox potential and substrate availability;

in the lower part of the oxycline, populations of microaerophilic chemoautotrophs and photoheterotrophs, each settle at their preferred depths according to respective microhabitats, while anoxygenic photoautotrophs bloom in the upper part of the anoxic and sulfidic zone, provided that enough light is available.

Geranyl Bacteriochlorophyll e

Among anoxygenic photoautotrophs, the Green Sulfur Bacterium Chlorobium phaeobacteroides strain BS1, previously cultivated from the chemocline of the Black Sea, has been found, to date, only in Faro Lake (Jörg Overmann, personal communication).

Interestingly, in correspondence of the blooms of GSB in Faro Lake, a Bacteriochlorophyll e (BChl e) homologue with an unusual retention time has been detected (Saccà et al. 2009): the geranyl ester of isobutyl/ethyl BChl e (Brendan Keely, personal communication). This homologue is esterified by the alcohol geraniol (C10) instead of farnesol (C15), which usually esterifies the primary BChl e homologues (Figure above).

The same homologue has been found in the Black Sea, firstly by Repeta et al. (1989) and, subsequently, by Manske et al. (2005). The ecological significance of this unusual bacteriochlorophyll homologue is still to be elucidated.

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