Marine benthic diatoms from
the 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:
- 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.
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).
At the end of september 2017, four samples were collected at the following stations:
- Plage de Cala Rotja (au NE de la plage de Cavalleria), profondeur 2,5- 3,5 mètres,
- Plage de Algaiarens, profondeur 3-4 mètres,
- Plage de Sa Caleta (près de la plage de Santandria), 2,5-3 mètres,
- Plage de Cala Blanca, 3-4 mètres.
On all stations, 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 11 collected samples has allowed to list 277 taxa belonging to 49 genera (see list of taxa ).
Twenty four genera are
represented by only one taxus. Fifty five taxa were not determined. The genus of four taxa was not determined.
The most represented genera are :
Genus Mastogloia : 51 taxa,
Genus Navicula : 35 taxa,
Genera Amphora and Halamphora : 28 taxa,
Genus Cocconeis : 24 taxa,
Genus Diploneis : 21 taxa,
Genus Nitzschia : 14 taxa,
Genus Pleurosigma : 11 taxa,
Genus Lyrella : 9 taxa.
Pictures of some of the collected species are presented in :
Some undetermined taxa are presented in :
The genus Mastogloia Thwaites ex WM Smith :
The analysis of the eleven samples has allowed to list 51 taxa belonging to the genus Mastogloia (see list of taxa). Seven taxa were not determined.
Thirty four are also présent in the sublittoral zone of the French Lesser Antilles. Two undetermined taxa (M. sp. 3, M. sp. 17 ) are présent at the French Lesser Antilles.
Pictures of some of the 51 Mastogloia taxa are presented in :
Conclusions :
The
samples collected at the end of September, 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) and in Dalmatia (299 taxa). It is the same thing for the specific
diversity of the genus Mastogloia
(respectively 58, 53 and 51 taxa). These moderate specific diversities go hand
in hand with a weak density of the collected diatom populations.
Fifty six among the 277 taxa present at Menorca were not observed
in our samples previously collected in the Mediterranean Sea.
At
the present time, a total of 790 taxa was
observed in the samples that we have collected in the Mediterranean Sea (diatoms from the Mediterranean Sea). Among these taxa, 254 have not been determined. One hundred and two taxa belong to the genus Mastogloia (see A check-list of the Mastogloia species from the Mediterranean area and Mastogloia from the Mediterranean Sea).