Marine benthic diatoms from Martinique

(sublittoral zone)
 
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Collection of the samples and analysis.

Twelve samples  were obtained in March-April 2008 and fifteen in March-April 2009, at depths between -3 and -9 meters, by snorkelling, as follows (from North towards South) :
- Anse Turin : 1 sample (medium sand),
- Anse à l'Ane : 1 sample (medium sand),
- Anse Noire : 2 samples (fine and medium sand),
- Anse Dufour : 9 samples (fine, medium and coarse sand),
- Grande Anse : 3 samples (fine sand),
- Anse d'Arlet : 5 samples (fine sand),
- Petite Anse : 2 samples (fine sand),
- Anse figuier : 3 samples (fine sand).

Cartemartinique 


Samples were collected on 5 of the 7 sites in 2010 and 2011 and on 3 of the 7 sites in 2012, 2013, 2014 and 2015.

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 fixed with acidic Lugol solution. Later, 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 12 samples collected in 2008, 463 taxa were listed, représenting 83 genera, 35 of which were représented by only one taxus.
In the samples, the number of taxa varies between 54 et 163.


In 2009, 301 taxa were listed.
In one sample obtained at the Anse d'Arlet at  2,5 meters deep, 240 taxa were observed, 54 of which belonging to the genus Mastogloia. At the opposite, the population collected at the Anse Dufour at  9 meters deep was composed, at about 90 %, by the 2 species Diploneis smithii et Diploneis fusca.

The most represented genera are the followings :
2008 2009 Total
(2008-2015)
Genres 83 87
Taxons 463 301 590 
Amphora 75 (16%) 39 (12.5%) 79 (13,4%)
Mastogloia * 47 (10.1%) 50 (16.5%) 90 (15,3%)
Nitzschia 53 (11.3%) 33 (10.6%) 62 (10.5%)
Navicula 44 (9.4%) 23 (7.4%) 51 (8.7%)
Cocconeis 26 (5.6%) 19 (6.1%) 34 (5.8%)
Diploneis 23 (5%) 15 (4.8%) 28 (4.8%)

* See list and Loir & Novarino 2013


The species

Pictures of some of the collected species are presented in
 :

Genera Achnanthes to Amphora
Genera Ardissonia to Dimeregrammopsis
Several species are not identified. Some of them are presented :

Non-identified species (1)
Non-identified species (2)


The 3 monoraphid genera Achnanthes, Cocconeis and Planothidium are represented respectively by  4, 26 et 4 taxa. Most of these taxa are present in low numbers.

The genera Mastogloia and Amphora were dominant by the number of taxa. Most of the Amphora taxa were present in low numbers. According to the sample, the representation of this genus varies between 10 and 25 %. Similarly, that of the genus Mastogloia (see the listLoir & Novarino 2013 and figures) varies between 3 and 18 % and that of the genus Nitzschia between 6 and 22 %.
In one sample collected at the Anse Dufour, it has been observed that some Amphora ocellata (between 2 and 24 cells ; see pictures) were included in mucilaginous bubbles. Some of these bubbles have a short tubular foot. This suggests that they were fixed to sand grains.

In the samples collected in 2015, 9 Mastogloia taxa, not mentionned in Loir & Novarino 2013, were observed (1 or 2 valves/frustules except for M. cyclops (5 valves/frustules)).


Conclusions

The data that we have obtained
point out that the diatom communities, present during march-april on the sandy sediments along the western coast of Martinique, are characterized by a high generic and specific diversity and by the dominance and the specific diversity of the genera Mastogloia and Amphora.

Taking into account the species collected, it appears that the diatom communities that we have collected
at Martinique (in march-april) and at Basse-Terre (in january and march) differ noticeably from those that we have collected at Marie-Galante (in march and may).

If the period of collect can explain partly the difference, likely, the mineralogical nature of the sediments (coral origin at Marie-Galante and abrasion of volcanic stones at Basse-Terre and at Martinique) plays 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 ** 295 540 590
Mastogloia 64 (21 %) 57 (10.6 %) 90 (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


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