Marine benthic diatoms from Basse-Terre 

(Guadeloupe, sublittoral zone)

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Collection of the samples and analysis.

Three samples (A-C) were obtained in January 2006 and five (D-H) in march 2007, at depths between -4 and -6 meters, by snorkelling, as follows :
- Petite Anse (north of Marigot), 3 samples : 1 sample (A) on fine sand, 1 sample  (B) on coarse sand and 1 sample (D) on medium sand,
- Anse Leroux (south of Deshaies) 2 samples : 1 sample (C) on coarse sand and 1 sample (E) on medium sand,
- Petite Anse (North of Pointe Noire), 1 sample (F) on medium sand,
- Anse de Malendure, 2 samples (G and H) on fine sand.
Cartebasseterre 

The surface of the sediment was scraped on a thickness of 3-4 mm using 50 ml Falcon tubes. Sampling was done in areas where a yellowish-braun film was present. After deep shaking of the samples, the diatoms were separated from the sediment by 2 or 3 differential sedimentations, then they were stored in the presence of 2% formaldehyde. The frustules were treated and prepared according to Loir (2004a and 2004b ; see bibliography).

Composition of the collected diatom populations 

In the 3 samples obtained in january 2006 (A-C), 248 taxa were listed, corresponding 68 genera.
In the 5 samples obtained in March 2007 (D-H), 367 taxa were listed corresponding to 76 genera. Two hundred and fifty eight of these taxa have not been observed in 2006.
So, the 8 samples have allowed to establish a list of 540 taxa and of 98 genera  present on the sublittoral sandy sediments along the western coast of Basse-Terre.

The  most represented genera in the whole of the samples are the followings :

Amphora : 78 taxa (14,5 %)

Nitzschia : 71 taxa (13,1 %)
Mastogloia*: 57 taxa (10,6 %)
Cocconeis : 49 taxa (9,1 %)
Navicula : 39 taxa (7,2 %)
Diploneis : 25 taxa (4,6 %)
* see list and Loir & Novarino 2013

Twenty nine genera are represented by only one species.

Two observations characterize the four samples A,B,C and D :


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One different species was dominant in each sample. At Petite Anse, Lyrella clavata represented around 98% of the frustules collected on fine sand (sample A), Amphora coffeaeformis represented around 95% of those collected on coarse sand (sample B) and Amphora elegans represented 92 % of those collected on medium sand (sample D) . Diploneis vacillans represented around 90% of the frustules from the Anse Leroux (sample C).
- Most of the other species were small species. In addition, the size of the frustules was frequently near the inferior limit indicated by the diagnoses .

In the four other samples, most of the species were also of small or medium size and, at least for the genus Cocconeis, the frustules had measurements near or below the inferior limit given by the diagnoses.

The species

Pictures of some of the collected species are presented in  :


Several taxa non- identified taxa are presented in :


Twenty seven taxa belong to the 19 centric genera 
Actinocyclus (2 taxons), Actinoptychus (1 t.), Anaulus (1 t.), Biddulphia (2 t.), Cyclotella (2 t.), Cymatosira (1 t.), Dimerogramma (2 t.), Dimerogrammopsis (1 t.), Eunotogramma (1t), Eupodiscus (1 t.), Odontella (1 t.), Paralia (1 t.), Plagiogramma (2 t.), Pleurosira (1 t.), Podosira (1 t.), Terpsinoe (2 t.), Thalassiosira (2 t.), Triceratium (2 t.) et Trigonium (1 t.).

Fourty five taxa belong to the 16 araphid genera
Ardissonia (3 taxons), Asterionella (2 t.), Climacosphenia (1 t.), Delphineis (5 t.), Diplomenora (1 t.), Fragilaria (3 t.), Grammatophora (8 t.), Hyalosira (3 t.), Hyalosynedra (1 t.), Licmophora (10 t.), Neosynedra (1 t.), Opephora (2 t.), Podocystis (1 t.), Psammodiscus (1 t.), Rhabdonema  (2 t.) et Toxarium (2 t.).

The 3 monoraphid genera  Achnanthes, Cocconeis andPlanothidium were represented respectively by 11, 49 and 4 taxa. Most of these taxa were present in low number.


Sixty one biraphid genera were represented by 404 taxa.
The genus Amphora was dominant by the number of taxa, most of which being present in low number. 
 

The genus Mastogloia

An inventory of the taxa belonging to the genus Mastogloia, present along the coast of Basse-Terre, was published in 2013 (Loir & Novarino 2013; figures). 

The preparations used for this inventory were of unsatisfactory quality. A new very thorough examination of the samples obtained in 2006 and 2007, realized in 2014, highlighted the presence of numerous Mastogloia taxa not observed previously (see list). Their total number of 57 differs little from those observed in Marie Galante (68) and in Martinique (60).

In Loir & Novarino 2013 (plate 23), 3 among the 5 figures of Mastogloia subaffirmata correspond in fact to Mastogloia cyclops ( présence of a single large stigma on one side of the central area).

Three not identified species, absent in Marie-Galante and in Martiniqua, are present in Basse-Terre. They were named M. sp. 19, M. sp. 20 and M. sp.c. The latter was already found in the Mediterranean Sea (Crete, Dalmatia, Greece, Sardinia)

In 2006, 37 taxa among the 57 ones, were not observed.

Some taxa are illustrated :

Genus Mastogloia (1)

Conclusions

The data obtained with the eight samples collected in the first meters of the sublittoral zone of Basse-Terre point out that the diatom communities, present during january and march on the sandy sediments along the western coast of this island, are characterized by a high generic and specific diversity and by the dominance and the specific diversity of the genus Amphora. However, in spite of this diversity, four samples contained populations which were, if not monospecific, at least dominated by one species. 
 
The analysis of the populations collected, on one hand in january and on the other in march (at one year interval), shows differences in the collected species. Seventy per cent of the species listed in march 2007 were not found in january 2006. We suggest that, although these differences could be due to the low number of samples, they could reflect variations throughout the year (seasonal variations ?).

Taking into account the species collected, it appears that the diatom communities that we have obtained at Basse-Terre (
in january and march) and at Martinique (in march-april) differ noticeably from those that we have obtained at Marie-Galante (in march and may). If the period of collect can explain partly the difference, the mineralogical nature of the sediments (coral origin at Marie-Galante and abrasion of volcanic stones at Basse-Terre and Martinique) could play an important role in the composition of the two diatom communities.

The dominant genera in Lesser Antilles :
                       
  Marie-Galante Guadeloupe Martinique
Genera 62 98 87
Taxa ** 295 540 560
Mastogloia 68 (23 %) 57 (10.6 %) 60 (11 %)
Nitzschia 31 (10.4 %) 71 (13.1 %) 62 (10.5 %)
Amphora 27 (9.2 %) 78 (14.5 %) 79 (13.4 %)
Cocconeis 25 (8.4 %) 49 (9.1 %) 34 (5.8 %)
Navicula 14 (4.7 %) 39 (7.2 %) 51 (8.7 %)
Diploneis 13 (4.4 %) 25 (4.6 %) 28 (4.8 %)

** See the list of taxa