Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
δ 15 N
16
15
14
13
12
11
10
0 10 20 30 40 50
Cephalothorax length (mm)
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
231
δ 13 C
-14
-15
-16
-17
-18
-19
0 10 20 30 40 50
Cephalothorax length (mm)
Figure 5 (a): Relation between δ 15 N muscle and size length of Norway lobster N. norvegicus (n = 32) (b):
Relation between δ 13 C muscle and size length of Norway lobster N. norvegicus (n = 32)
The results for Nephrops norvegicus (n = 32) showed a slight but significant relation between
size and δ 15 N (r² = 0.22, p < 0.001), with values averaging 11‰ (SD = 0.31). Conversely, a strong
correlation (r² = 0.74, p < 0.0001) was found between size and δ 13 C, with an increase of 3‰ from
shorter to longer individuals (Table 2).
Table 2: Linear regression parameters (δ 15 N or δ 13 C) = a x size length (total or cephalothorax) + b. r² is
regression coefficient and p is the statistical test p value * significant value
δ 15 N δ 13 C
Taxa a b r² p a b r² p
Merluccius merluccius 0.0804 11.610 0.7473 < 0.0001* 0.0554 -18.891 0.5687 < 0.0001*
Nephrops norvegicus 0.0214 10.479 0.2239 < 0.001* 0.0688 -18.397 0.7488 < 0.0001*
Munida sarsi 0.0727 9.455 0.3610 < 0.0001* 0.0742 -17.958 0.4198 < 0.0001*
Trisopterus minutus 0.2702 8.909 0.8793 < 0.0001* -0.0088 -16.951 0.0083 0.421
Micromesistius poutassou 0.0472 11.260 0.2479 0.164 -0.0367 -17.181 0.0531 0.031
Trachurus trachurus 0.0558 11.022 0.1060 0.030 0.1759 -21.618 0.3361 0.484
This analysis was also conducted for the by-catch species Munida rugosa (n = 22 ; Figure 6 a
and b), Micromesistius poutassou, Trisopterus minutus and Trachurus trachurus (Figure 7 a and b).
On the whole, M. rugosa displayed a similar trend as N. norvegicus for both carbon and nitrogen. δ 15 N
showed low significant variability with size, while δ 13 C was correlated with size (Table 2).
M. poutassou and T. trachurus displayed the same pattern for δ 15 N and δ 13 C (no correlation with
increasing size ; Table 2). Finally, this analysis for T. minutus showed no correlation between δ 13 C
values and individual size, whereas a strong correlation existed between δ 15 N values and individual
size (r² = 0.87, p < 0.0001).