Effect of depth gradients on fish trophic relationships in the English Channel Pierre Cresson a, Bruno Ernande a, Carolina Giraldo b, Sébastien Lefebvre b, Manuel Rouquette a, Morgane Travers Trolet a a : Ifremer, Centre Manche-Mer du Nord, Boulogne-sur-Mer b : Laboratoire d’Océanologie et de Géosciences (LOG), Université des Sciences et Technologies de Lille (USTL) et Université du Littoral Côte d’Opale (ULCO), Wimereux
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Benthic / pelagic coupling “Any process that may influence both pelagic and benthic habitat in aquatic systems” (Baustian et al. 2014) • Crucial mechanisms for the functioning of both entities (e.g. nutrient and matter fluxes) • May result from biogeochemical cycling, organism movement and trophic interactions, and is controlled by physical factors (stratification / depth)
• Two-way mechanism : pelagos to benthos (particle sinking) or benthos to pelagos
Baustian et al. 2014
2
Benthic / pelagic coupling
3
“Any process that may influence both pelagic and benthic habitat in aquatic systems” (Baustian et al. 2014) • Crucial mechanisms for the functioning of both entities (e.g. nutrient and matter fluxes) • May result from biogeochemical cycling, organism movement and trophic interactions, and is controlled by physical factors (stratification / depth)
• Two-way mechanism : pelagos to benthos (particle sinking) or benthos to pelagos
Main current challenges about BPC : - Influence of benthos on pelagos ? - Effect of environment studies at large spatial scale (Ings et al. 2009) - Major habitat couplers (Schindler and Scheuerell 2002)? Baustian et al. 2014
What about the Eastern English Channel ?
4
Based on results of Kopp et al. 2015
Pelagic OM sources Bentho-pelagic coupling
Pelagic OM sources
Mackerel Scomber scombrus
Benthic OM sources Bentho-pelagic decoupling
Benthic OM sources Plaice Pleuronectes platessa
0m
100 m Depth
What about the Eastern English Channel ?
5
Based on results of Kopp et al. 2015
Pelagic OM sources Bentho-pelagic coupling
Pelagic OM sources
Mackerel Scomber scombrus
Benthic OM sources Bentho-pelagic decoupling
Working hypotheses : 1 . Predominance of benthic sources at shallow sites due to high productivity 2. Differentiation between benthic and pelagic species when depth increases
Benthic OM sources Plaice Pleuronectes platessa
0m
100 m Depth
What about the Eastern English Channel ?
6
Based on results of Kopp et al. 2015
Pelagic OM sources Bentho-pelagic coupling
Pelagic OM sources
Mackerel Scomber scombrus
Benthic OM sources Bentho-pelagic decoupling
Working hypotheses : 1 . Predominance of benthic sources at shallow sites due to high productivity 2. Differentiation between benthic and pelagic species when depth increases 0m
Benthic OM sources Plaice Pleuronectes platessa
To be confirmed at large spatial scale… Depth
100 m
C and N stable isotopes Main properties : - δ13C benthic < δ13C pelagic - δ diet δ consumer - C : conserved / N : increase
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Mixed contributions of benthic and pelagic sources
Benthic food web
Pelagic food web B>P
Appropriate tool to discriminate pelagic and benthic respective influences in marine food webs
δ15N trophic level
B
TL 3
BP
Appropriate tool to discriminate pelagic and benthic respective influences in marine food webs Isotopic mixing models : SI similarity between source and fish important dietary source allows estimating the % of contribution of each source
δ15N trophic level
B
TL 3
B
