Spatial and seasonal variability of pico-, nano- and microphytoplankton at the bottom seawater in the north coast of Sfax, Eastern Mediterranean Sea
Résumé
In the frame of the Taparura Project, we studied the
distribution of pico-, nano- and microphytoplankton communities
in relation to environmental variables at 18 stations
sampled during four coastal cruises conducted between
October 2009 and July 2010 at the bottom, on the north coast
of Sfax (Tunisia, Eastern Mediterranean Sea). The restoration
effect on coastal ultraphytoplankton (<10 μm) and
microphytoplankton (<200 μm) was investigated using conventional
flow cytometry and inverted microscopy. Flow cytometry
analysis of ultraphytoplankton resolved six groups
(Prochlorococcus, Synechococcus, nanoeukaryotes and three
distinct subgroups within picoeukaryotes). In addition to these
autotrophic groups, two unknown groups were characterised
on the north coast. Picophytoplankton abundance shifted from
a summer dominance of Synechococcus to a dominance of
picoeukaryotes and Prochlorococcus during spring.
Nanoeukaryotes were the most abundant in spring.
Microphytoplankton was resolved into five groups, labelled
Bacillariophyceae, Dinophyceae, Cyanobacteriae,
Euglenophyceae and Chlorophyceae. A total of 90
microphytoplankton species were identified in all stations,
with an overwhelming abundance of large diatoms, a typical
trait of benthic communities (Coscinodiscus sp.,
Grammatophora sp., Navicula sp., Pleurosigma sp.,
Striatella unipunctata …). Results collected in this study are
favouring a beneficial impact on the ecosystem of the Sfax
north coast restoration achieved by the Taparura Project.