Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
on the bottom. Consequently, the only organic material for benthic primary consumers is assumed to
be the POM sedimenting from upper water layers and therefore this is designated as the first trophic
level (TL1).
Results
Species for isotopic analysis were selected as those which were both dominant in abundance
and biomass and also accessible for predation by the two main target species. Nephrops norvegicus,
Munida rugosa, Liocarcinus depurator and Microchirus variegatus were found in all samples and
composed 52% of the total biomass (Table 1). Demersal and benthic fishes constituted 36% of the
total biomass (52.96 g dry weight•1000 m -2 ). Epibenthos mean biomass (mostly Crustacea: 84%) was
93.36 g dry weight•1000 m -2 , and mean total abundance was 115 individuals•1000 m -2 .
Table 1: Taxonomic list of the major fauna collected at eight stations of the “Grande Vasière”. The mean
weight is a dry weight, the% weight is the biomass part of the species in the total fauna collected biomass.
(SD): standard deviation.
Dominant fauna
%
Occurrence
Mean weight
g•1000 m -2 (SD)
228
%
Weight
Mean number
ind•1000 m -2 (SD)
Nephrops norvegicus 100 29.07 (13.67) 19.87 20.31 (12.22)
Munida rugosa 100 21.57 (20.21) 14.74 32.17 (31.21)
Liocarcinus depurator 100 16.50 (13.37) 11.28 12.14 (10.46)
Microchirus variegatus 100 9.40 (4.87) 6.43 2.26 (1.28)
Arnoglossus laterna 87.5 10.85 (8.19) 7.41 5.16 (5.85)
Enchylopsus cimbrius 87.5 10.23 (7.05) 6.99 1.51 (0.99)
Goneplax rhomboides 87.5 8.83 (9.33) 6.03 5.08 (4.98)
Alpheus glaber 87.5 0.63 (0.53) 0.43 4.98 (4.25)
Nucula sulcata 75 2.26 (2.54) 1.55 3.82 (4.71)
Lesueuriogobius friseii 75 1.92 (3.08) 1.31 3.72 (5.91)
Crangon allmani 75 0.61 (0.52) 0.42 4.89 (2.84)
Macropodia tenuirostris 75 0.59 (1.19) 0.41 5.64 (12.01)
Merluccius merluccius 62.5 8.13 (11.63) 5.56 1.03 (1.03)
Venus ovata 62.5 0.64 (0.98) 0.44 0.55 (0.66)
Squilla desmaresti 50 0.39 (0.48) 0.26 0.74 (0.94)
Chlorotoccus crassicornis 50 0.31 (0.43) 0.21 1.19 (1.49)
Callyonimus lyra 37.5 1.34 (2.01) 0.92 0.22 (0.32)
Brissopsis lyrifera 37.5 0.96 (1.48) 0.66 0.29 (0.43)
Capros aper 37.5 0.36 (0.58) 0.24 0.58 (0.98)
Callyonimus maculatus 37.5 0.34 (0.56) 0.23 0.36 (0.66)
Sternapsis scutata 37.5 0.06 (0.09) 0.04 0.22 (0.32)
Identification of the trophic groups
Average stable nitrogen isotope ratios ranged from 4.1‰ (POM surface) to 14.5‰
(M. merluccius), corresponding to four main trophic levels. A Student test (α = 0.05) indicated no
significant difference between surface and bottom POM.
Analysis showed a wide range of δ 13 C isotope signatures, from -23.7‰ (POM surface) to -
15.4‰ for the crab Goneplax rhomboides. δ 13 C, like δ 15 N, showed no significant difference (Student