Food-web data
We studied the trophic network corresponding to the upper part of the
Celtic Sea trophic network (TL>=2), defined at genus or
species resolution and restricted to interactions between most abundant
and common taxa observed during the scientific survey EVHOE (see
Mérillet et al., 2020). Trophic links between taxa were taken from the
literature review conducted in Hernvann et al. (2020), keeping the
information at the taxon’s level. We collected isotopic measurements for
69 taxa of the most commonly found in bottom trawls in the Celtic Sea
(EATME project). We applied a lipid correction for the taxa with a C/N
>3.5, following Sweeting, Polunin, & Jennings (2006). We
then applied a baseline correction based on isotopic signatures ofAequipecten opercularis , using bottom temperature for δ13C
(Barnes et al. 2009) and using bottom temperature and salinity
correction for δ15N (Jennings & van der Molen 2015). The performance of
the correction was then checked by looking at the correlation between
real and corrected values for other bivalves (i.e. Pecten
maximus , Aequipecten opercularis , Pseudamussium peslutraeand Pseudamussium clavatum ). Trophic levels TL of taxa i were
computed from Post (2002) equation, as follows:
\(\text{TL}_{i}=\ \frac{\delta{15N}_{i}-\ \delta{15N}_{\text{base}}}{3.4}+\text{TL}_{\text{base}}\)
with δ15Ni the corrected δ15N value for the taxa i and δ15Nbase the mean
of the δ15N base values of bivalves (TLbase = 2).
We computed several metrics informing on the structural properties of
the network. Connectance (L/S2), computed from the number of links (L)
and the number of species (S), gives information on how densely
connected is trophic network. Our network of 69 species and 559 links
has average values of connectance (0.12), with connectance ranging from
0 to 1, with 0 indicating the least possible number of interactions
(Delmas et al. 2019). For a complete description of these metrics
see Delmas et al. (2019) and Kortsch et al. (2018).