1989 ; Cornet et al, 1983), on the adjacent slope (Elizalde, 1994 ; Elizalde
et al., 1993 ; Dauvin et ai, 1995) and within the Cap-Ferret canyon down
to approximately 3000 m depth (Sorbe, 1999). In that area, distinct assembiages were described, demonstrating a decreasing faunal abundance
with depth and a higher biodiversity on bathyal bottoms.
So far, few studies were conducted on benthic communities from the
Capbreton canyon (see Le Danois, 1948 ; Sorbe, 1990), although recent
investigations revealed that this Gouf-type submarine valley sheiters
abundant benthic populations of supposedly rare species with respect to
peculiar environmental conditions (Marquiegui & Sorbe, 1999). Within
the framework of a new research programme dealing with bottom oxygenation and benthic communities in the Capbreton area (Oxybent
oceanographic cruises), we took the opportunity to periodically sample
several sites in order to describe temporal changes in the structure of
their suprabenthic assemblages. This report focuses on the first observations on these assemblages from the analysis of a sample seties taken
during wintertime.
Material and methods
Figure 1 shows the study area located in the south-eastem part of the
bay of Biscay and the geographical position of the sampling stations
on the continental shelf (St. D, 162 m, northern margin of the canyon), within the canyon (St. (i’, 308 m ; St. E, 766 m ; St. F7, 812 m)
and on the slope (St. B, 555 m and St. A, 987 m). All the sampling stations are located on muddy sediment, with a weak sandy fraction at station F7. According to Tauzin (1974), all the sampling stations located
below 500 m are under the influence of Mediterranean water characterized by a temperature of 9-10.5°C, a high salinity (35.80) and a low
oxygen content (minimum value slighdy inferior to 4.38 ml 1
1 at about
850 m water depth). Ogawa & Tauzin (1973) described the physicochemical environment at the water-sediment interface all along the canyon. The near-bottom waters generally showed a low oxygen content due
to their stagnation westward from the meridian 1 °38’ W. Their mean level
of oxygen saturation was about 50% but locally some values were less than
25°/» (hypoxia). Furthermore, between 1°50’W and 1°58’W, very low
oxyrgen contents were measured in the near-bottom waters (minimum
value at 20 cm above the sea floor: 1.96 ml 11 ) suggesting a tendency to
confmement in this sinuous part of the canyon. Westward from the meridian 2° W, the near-bottom waters showed a high oxygen content (5.74
ml 1 -1 at about 1600 m depth) probablv due to a better circulation of water masses in this enlarged part of the canyon (oxygen saturation level:
75%). Tauzin (1974) measured the organic carbon content (percentage of
drv sediment) of surficial sediments all along the bottom and the flanks
of the canyon. The observed values fluctuated between 0.44 and 5.39%
and an organic-rich area was detected at a bathymetric level located just
above the aforementioned confinement area.
88
et al., 1993 ; Dauvin et ai, 1995) and within the Cap-Ferret canyon down
to approximately 3000 m depth (Sorbe, 1999). In that area, distinct assembiages were described, demonstrating a decreasing faunal abundance
with depth and a higher biodiversity on bathyal bottoms.
So far, few studies were conducted on benthic communities from the
Capbreton canyon (see Le Danois, 1948 ; Sorbe, 1990), although recent
investigations revealed that this Gouf-type submarine valley sheiters
abundant benthic populations of supposedly rare species with respect to
peculiar environmental conditions (Marquiegui & Sorbe, 1999). Within
the framework of a new research programme dealing with bottom oxygenation and benthic communities in the Capbreton area (Oxybent
oceanographic cruises), we took the opportunity to periodically sample
several sites in order to describe temporal changes in the structure of
their suprabenthic assemblages. This report focuses on the first observations on these assemblages from the analysis of a sample seties taken
during wintertime.
Material and methods
Figure 1 shows the study area located in the south-eastem part of the
bay of Biscay and the geographical position of the sampling stations
on the continental shelf (St. D, 162 m, northern margin of the canyon), within the canyon (St. (i’, 308 m ; St. E, 766 m ; St. F7, 812 m)
and on the slope (St. B, 555 m and St. A, 987 m). All the sampling stations are located on muddy sediment, with a weak sandy fraction at station F7. According to Tauzin (1974), all the sampling stations located
below 500 m are under the influence of Mediterranean water characterized by a temperature of 9-10.5°C, a high salinity (35.80) and a low
oxygen content (minimum value slighdy inferior to 4.38 ml 1
1 at about
850 m water depth). Ogawa & Tauzin (1973) described the physicochemical environment at the water-sediment interface all along the canyon. The near-bottom waters generally showed a low oxygen content due
to their stagnation westward from the meridian 1 °38’ W. Their mean level
of oxygen saturation was about 50% but locally some values were less than
25°/» (hypoxia). Furthermore, between 1°50’W and 1°58’W, very low
oxyrgen contents were measured in the near-bottom waters (minimum
value at 20 cm above the sea floor: 1.96 ml 11 ) suggesting a tendency to
confmement in this sinuous part of the canyon. Westward from the meridian 2° W, the near-bottom waters showed a high oxygen content (5.74
ml 1 -1 at about 1600 m depth) probablv due to a better circulation of water masses in this enlarged part of the canyon (oxygen saturation level:
75%). Tauzin (1974) measured the organic carbon content (percentage of
drv sediment) of surficial sediments all along the bottom and the flanks
of the canyon. The observed values fluctuated between 0.44 and 5.39%
and an organic-rich area was detected at a bathymetric level located just
above the aforementioned confinement area.
88