Marine benthic diatoms from Sardinia

(Tyrrhenian Sea, sublittoral zone)


Collection of the samples

Four samples were collected by schnorkelling between 3 and 5 meters deep, at the end of October 2010, on the north-east littoral of the island (between San Teodoro and Posada; 40°43'31.15" N, 9°42'53.18" E).
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 with acidic Lugol solution. The frustules were treated and prepared according to Loir (2004a et 2004b; see Bibliography).

Composition of the diatom populations :

The analysis of the 4 samples has allowed to list a total de 271 taxa, belonging to 46 genera (see list of taxa). Twenty four genera were represented by only one taxus. Sixty six taxa were not identified. The genus  of 2 taxa was not determined.

The most represented genera are :

Genus Mastogloia : 48 taxa,
Genus Nitzschia : 34 taxa,
Genus Amphora (and Halamphora) : 31 taxa,
Genus Navicula : 29 taxa,
Genus Cocconeis: 27 taxa,
Genus Diploneis : 19 taxa,
Genus Lyrella : 9 taxa,
Genus Licmophora : 6 taxa.

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

Pictures of some of the collected taxa are presented in :

Genera Amphora to Cocconeiopsis

Several non-identified taxa are presented in :

Non-identified taxa 1
Non-identified taxa 2

The genus Mastogloia Thwaites ex WM Smith :

The 4 samples have allowed to list 48 taxa belonging to the genus Mastogloia  (see list of taxa). Eight taxa have not been identified.

Thirty seven among the 40 identified taxa are also present in the sub-littoral zone either in Crete, either in Dalmatia, either in Greece or in 2 or 3 of these countries. Thirty seven taxa are also present in the French Lesser Antilles.
The valves of an half of the identified taxa have measurements near or below the inferior limit indicated by the diagnoses. Five taxa have a size clearly below the inferior limit.

Some of the Mastogloia taxa are presented in :

The genus Mastogloia (1)
The genus Mastogloia (2)

Conclusions :

The 4 samples collected at the end of October in a very restricted area of the sardinian littoral have allowed to establish a likely incomplete inventory of the diatom taxa present in the first meters of the sub-littoral zone of this coast. Nevertheless, they have allowed to evidence the occurence of a great specific diversity and the presence of numerous Mastogloia taxa.

A total of 649 taxa (220 have not been identified) was listed in the samples collected in Sardegna, in Dalmatie, in Greece and in Crete (see list of diatoms from Mediterranean Sea). In these samples, we have listed a total of 104 taxa belonging to the genus Mastogloia (see list Mastogloia from the Méditerranean Sea).

As we have already observed for the genus Cocconeis present in the sub-littoral zone of Brittany (Loir, 2007 ; see Bibliography) and of Guadeloupe (see Basse-Terre), as well as for several species present in the same zone in Martinique (see Martinique), two tens of Mastogloia taxa collected in Sardegna on the sandy sediments in the sub-littoral zone present measurements near or below the inferior limit indicated in the diagnoses.

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