Marine benthic diatoms from Crete

(Mediterranean Sea, sublittoral zone)


Collection of the samples

Two samples were collected by schnorkelling at the beginning of October 2011, at the north-east of the island, northward of Agios Nicolaos (35° 14'21.32" N, 25° 44' 06.80 E) between 3 and 5 meters deep. 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 and 2004b ; see bibliography).

Composition of the collected diatom populations 

The analysis of the 2 samples has allowed to list 344 taxa, représenting 60 genera  (see list of taxa). Thirty five genera were represented by only one taxus. Ninety taxa were not identified and the genus of 4 taxa was not determined.

The most represented genera are :
Genus Mastogloia : 67 taxa,
Genus Nitzschia : 47 taxa,
Genus Amphora (and Halamphora): 38 taxa,
Genus Navicula : 34 taxa,
Genus Cocconeis: 25 taxa,
Genus Diploneis : 17 taxa,
Genus Lyrella : 10 taxa,
Genus Pleurosigma : 8 taxa,
Genus Licmophora : 7 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  :

Genera Achnanthes à Amphora
Genera Ardissonia à Cocconeis
Genera Cylindrotheca à Licmophora
Genera Luticola à Navicula
Genus Nitzschia
Genera Opephora à Toxonidea

Several not identified taxa are presented in :

Non-identified taxa 1
Non-identified taxa 2

The genus Mastogloia Thwaites ex WM Smith :

The 2 samples have allowed to list 67 taxa belonging to the genus Mastogloia  (see list of taxa). Sixteen taxa  have not been identified.

Thirty eight among the 51 identified taxa are present in the sub-littoral zone of Sardegna and 33 are present in Dalmatia. Forty four are also present in the sub-littoral zone of the French Lesser Antilles.

Five among the 19 non-identified Mastogloia taxa (M. sp. 3, M. sp.4, M. sp. 6, M. sp. 8 and M. sp. 15) are  present in the sub-littoral zone of the French Lesser Antilles. Two taxa (sp. 6 and 9) are present in Dalmatie and two taxa (M. sp. 4 et M. sp. 15) in Sardegna.

The valves of twenty six identified Mastogloia taxa have measurements near or below the inferior limits given by the diagnoses.

Some of the 67 Mastogloia taxa are presented in :

Genus Mastogloia 1
Genus Mastogloia 2

Conclusions :

Both samples collected at the beginning of October in a very limited zone of the littoral of Crete have allowed to establish a probably incomplete inventory of the diatom taxa present in the first meters of the sub-littoral zone on this coast. They allow nevertheless to highlight 1) a high specific diversity and 2) the presence of numerous taxa belonging to the genus Mastogloia.

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

It would be interesting to know if the presence in Crete of some diatom species, does not result from a migration by the Suez Canal (for 150 years, seaweeds, invertebrates and fishes passed by this canal from the Red Sea to the Mediterranean Sea (this phenomenon bears the name of lesseptienne migration).

As we have already noticed for the genus Cocconeis from Brittany (Loir, 2007; see Bibliography) and from Guadeloupe, as well as for numerous species from Martinique, and Sardegna, several species collected in Crete have have measurements near or below the inferior limits given by the diagnoses.

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