Marine benthic diatoms from Dalmatia

(Croatia, Eastern Adriatic Sea, sublittoral zone)


Collection of the samples

Six samples were collected by schnorkelling between 3 and 5 meters deep at the end of September-beginning of October 2012, at about 15 km southeastward of Dubrovnik (42°36'37.98"N, 18°13'23.42"E and 42°36'28.66"N, 18°13'27.05"E; 4 samples) and at Lopud Island (42°41'14.40N, 17°56'15.98E; 2 samples).
In May 2017, two samples were collected at 2.5 meters deep, at about 8 km southeastward of Split (43°29'44.71N, 16°32'08.85E).
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 diatom populations :

The analysis of the samples has allowed to list 315 taxa, belonging to 58 genera (see list of taxa). Twenty one genera were represented by only one taxus. Sixty one taxa were not identified.

The most represented genera are :

Genus Mastogloia : 51 taxa,
Genus Amphora (and Halamphora) : 34 taxa,
Genus Nitzschia : 30 taxa,
Genus Cocconeis: 23 taxa,
Genus Navicula : 22 taxa,
Genus Diploneis : 18 taxa,
Genus Licmophora : 12 taxa,
Genus Pleurosigma : 8 taxa.

The valves or frustules of 13 freshwater diatom taxa, belonging to the genera Cocconeis, Cyclotella, Cymatopleura, Cymbella, Diatoma, Gomphonema et Synedra were found. Likely these diatoms were present in streams and they were carried into the sea.

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

Pictures of some of the collected species are presented in :

Genera Actinocyclus à Cymatosira
Genus Amphora
Some non-identified taxa are presented in :

Non-identified taxa

The genus Mastogloia Thwaites ex WM Smith :
The samples have allowed to list 51 taxa belonging to the genus Mastogloia (see list of taxa). Six were not identified.

Thirty five identified taxa are present in the French Lesser Antilles. Two non-identified Mastogloia taxa (M. sp. cf. exilis (named M. sp. 6), M. sp. 17) are also present in the French Lesser Antilles.

About one third of the Mastogloia taxa have frustules/valves the size of which is near or below the inferior limit given by the diagnoses.

Some of the 51  Mastogloia taxa are presented in :

Genus Mastogloia (1)
Genus Mastogloia (2)

Conclusions :

The eight samples collected in two restricted zones of the dalmatic coast have allowed to establish a probably incomplete inventory of the diatoms present in the first meters of the sub-littoral zone of this region. Nevertheless, 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 790 taxa (254 were not identified), was listed in the samples collected in Sardegna, in Dalmatia, in Greece, in Crete, in Corfu and in Menorca (list diatoms Mediterranean Sea). In the whole of the samples collected in these six countries we have listed a total of 102 taxa belonging to the genus Mastogloia (see A check-list of the Mastogloia species from the Mediterranean area and list Mastogloia from the Méditerranean Sea).

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