Marine benthic diatoms from

the southern coast of Menorca

(Balears Islands, Mediterranean Sea, sublittoral zone)

Collection of the samples

Five samples were collected by schnorkelling at the end of September 2015, at the following stations along the southern seaside of Menorca which is lined by Miocene limestones and the sand is there fine and of calcareous nature:
- Punta Prima beach,  2.5-4 meters deep,
- Benibecca beach, 2.5-3 meters,
- Cala'n Porter beach, 2.5-4 meters,
- Son Saura beach, 2.5-3 meters,
- Cala en Turqueta beach, 2.5-4 meters.

It has not been possible to collect samples along the northeastern coast which is lined by primary and secondary grounds (schists, wills).

At the end of September 2016, two samples were collected, one at the Cala Macarella (southern coast) and one at the beach of Algaairens (northwestern coast).

The diatomic populations were always insufficiently dense to show itself by one yellow-brown tint of the surface of the sand.

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 analysis of the 7 collected samples has allowed to list 215 taxa belonging to 45 genera (see list of taxa ).
Twenty two genera are represented by only one taxus. Thirty eight taxa were not determined. The genus of two taxa was not determined.

The most represented genera are :
Genus Mastogloia : 49 taxa,
Genus Cocconeis : 21 taxa,
Genera Amphora and Halamphora : 19 taxa,
Genus Navicula : 19 taxa,
Genus Diploneis : 18 taxa,
Genus Pleurosigma : 9 taxa,
Genus Lyrella : 6 taxa,
Genus Nitzschia : 8 taxa.

Pictures of some of the collected species are presented in  :
Genera Actinocyclus to Climacosphenia
Genera Cocconeis and  Diploneis
Genera Fallacia to Licmophora
Genera Lyrella to Nitzschia
Genera Petroneis to Triceratium

Some undetermined taxa are presented in :
Undetermined taxa

The genus Mastogloia
Thwaites ex WM Smith :

The analysis of the seven samples has allowed to list 49 taxa belonging to the genus Mastogloia (see list of taxa). Fourteen taxa were not determined.

Twelve taxa among the 34 determined taxa are présent in the sublittoral zone of Corfou, Crete, Dalmatia, Greece and  Sardegna. Thirty two are also présent in the sublittoral zone of the French Lesser Antilles.
Three Mastogloia taxa among the 10 undetermined taxa (M. sp. 15, M. sp. 19 and M. sp. C ) are présent at the French Lesser Antilles. Five were already observed in the Mediterranean Sea  (M. sp. C, M. sp. D, M. sp. E, M. sp. K  and M. sp. N; see list of taxa)
Pictures of some of the 49 Mastogloia taxa are presented in :

Genus Mastogloia 1
Genus Mastogloia 2
Genus Mastogloia 3

Conclusions :

The samples collected at the end of September 2015 and 2016, along the southern and northwestern seasides of Menorca have allowed to establish a first inventory of the diatoms present on the sandy bottoms, in the first meters of the sublittoral zone of this island. They highlight a global specific diversity on this coast lower than those observed in Corfou (298 taxa), in Crete (344 taxa), in Dalmatia (299 taxa) and in Sardegna (271 taxa) and near that observed in Greece (190 taxa). It is the same thing for the specific diversity of the genus Mastogloia (respectively 63, 67, 55, 48 et 57 taxa). These moderate specific diversities go hand in hand with a weak density of the collected diatom populations. It would be interesting to be able to collect samples on the northeastern seaside of Menorca where the mineralogical nature of sands differs most probably.

Fourty four among the 215 taxa present at Menorca were not observed in our samples previously collected in the Mediterranean Sea.

At the present time, a total of 772 taxa was observed in the samples that we have collected in the Mediterranean Sea (diatoms from the Mediterranean Sea). Among these taxa, 239 have not been determined. One hundred and eleven taxa belong to the genus Mastogloia (see list of Mastogloia from the Mediterranean Sea).

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