Ecologie des foraminifères planctoniques du golfe de Gascogne ...

tel-00480660, version 1 - 4 May 2010
Chapitre II
described also for other ocean margins of similar latitude (Lidz, 1966; Gibson, 1989).
However, standing stocks were low (Appendix B: in April, average number at 0-100 m of 230
specimens m -3 at Station WH) compared to the pelagic North Atlantic (Schiebel and
Hemleben, 2000; 720 specimens m -3 ). Albaina and Irigoien (2007) report a maximum of 846
specimens m -3 during spring 2004, indicating that maximum abundance of planktic
foraminifera was possibly not sampled in April 2007 (Appendix B: max. at 0-100 m of 526
specimens m -3 at Station WH), and confirming high spatial and temporal variability of PF
abundance at the southern Bay of Biscay (Fig. II-4).
Figure II-8: Chlorophyll-a (mg m -3 ) in the Bay of Biscay, from SeaWiFs images
(http://oceancolor.gsfc.nasa.gov): a) April 2007, before PECH 3 (Table II-1), showing high
phytoplankton production in the central part of the Bay of Biscay. b) November 2007, before PECH 4,
showing enhanced phytoplankton production along the coast of the south-eastern Bay of Biscay, in
comparison to April, and low phytoplankton production in the central Bay of Biscay. Sampling
locations are indicated by black dots (Fig. II-1).
7.2. Seasonal changes in plankton production and abundance of living planktic
foraminifera
In the Bay of Biscay, diatoms and coccolithophores are major contributors to phytoplankton
mass production in spring (e.g., Labry et al., 2004). Compared to spring, plankton production
during summer is low, and less marked and more dispersed in autumn (e.g. Longhurst, 1998;
Ceballos and Alvarés-Marqués, 2006). As a consequence, three different seasonal conditions
of planktic foraminiferal production can be distinguished in the south-eastern Bay of Biscay :
1) High production during spring, 2) low production during summer, and 3) sporadic
production during fall (Fig. II-4 and II-5).
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