Marine benthic diatoms from Corfou

(Ionian Sea, sublittoral zone)

Collection of the samples

Six samples were collected by schnorkelling at the end of September 2014, at the following stations along the seaside of Corfou, of Paxos and of Antipaxos :
- Gouvia beach, silt, 2,5 meters deep,
- Antipaxos, calcareous sand, 2,5-3 meters,
- Paxos, sand, 2,5-4 meters,
- Ipsos beach, silty sand, 3-4 meters,
- Sidari beach, dense silty sand, 2 meters,
- Paleokastritsa beach, sand, 3-5 meters.

The surface of the sediment was scraped on a thickness of 3-4 mm using 50 ml Falcon tubes.  After dilution with 0.5 volume of sea water, the samples were shaken deeply and the diatoms were separated from the sediment by 2 or 3 differential sedimentations, then fixed and stored in acidic Lugol solution. The frustules were treated and prepared according to Loir (2004a and 2004b ; see bibliography).

Composition of the collected diatom populations 

The samples collected at Gouvia, Antipaxos and Sidari contained only scarce diatoms and they were not used.

The analysis of the 3 samples obtained at Ipsos, Paxos and Paleokastritsa has allowed to list 298 taxa, représenting 69 genera (see list of taxa). Between 114  and 144 taxa were observed in every sample.

Fourty one genera were represented by only one taxus. Fourty five taxa were not identified and the genus of 7 taxa was not determined.

The most represented genera are :

Genus Mastogloia : 63 taxa,
Genera Amphora and Halamphora : 36 taxa,
Genus Nitzschia : 28 taxa,
Genus Diploneis : 22 taxa,
Genus Navicula : 18 taxa,
Genus Cocconeis: 16 taxa,
Genus Pleurosigma : 13 taxa,
Genus Lyrella : 8 taxa,
Genus Gyrosigma : 5 taxa.

Many taxa have measurements near or below the inferior limit given by the diagnoses.

Pictures of some of the collected species are presented in  :

Genres Amphora à Cistula
Genres Cocconeis à Diploneis
Genres Entomoneis à Lyrella
Genres Navicula à Nitzschia
Genres Petroneis à Tryblionella

Unidentified taxa

The genus Mastogloia Thwaites ex WM Smith :

The 3 samples have allowed to list 63 taxa belonging to the genus Mastogloia  (see list of taxa). Fourteen taxa  have not been identified.

Sixteen taxa among the 49 identified taxa are also present in the sub-littoral zone of Sardegna, Crete, Dalmatia and Greece. Forty four are also present in the sublittoral zone of the French Lesser Antilles.

Four taxa among the 19 non-identified Mastogloia taxa (M. sp. 3, M. sp. 6, M. sp. 9 and M. sp. 15) are  present in the sublittoral zone of the French Lesser Antilles. The taxus M. sp. C  is present in the sub-littoral zone of Guadeloupe and also of Crete, Dalmatia and Greece.
The valves of several identified Mastogloia taxa have measurements near or below the inferior limits given by the diagnoses.

Some of the 63 Mastogloia taxa are presented in :

Genre Mastogloia 1
Genre Mastogloia 2
Genre Mastogloia 3 (unidentified species)

Conclusions :

The samples collected at the end of september 2014 in some stations of the sublittoral zone of Corfou and of Paxos have allowed to establish a first inventory of the diatoms present on the sandy bottoms, in the first meters of the sublittoral zone of these islands. They allowed to highlight the diversity of the benthic diatom populations in this zone and, especially, the presence of several tens of Mastogloia species.

A total of 723 taxa (231 were not identified), was listed in the samples collected in Sardegna, Dalmatia, Greece, Crete and Corfou (see list of diatoms from Mediterrenean Sea). In the whole of the samples collected in these five countries we have listed a total of 111 taxa belonging to the genus Mastogloia (see list Mastogloia from the Méditerranean Sea).

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