Lower trophic levels and detrital biomass control the Bay of Biscay continental shelf food web: Implications for ecosystem management

Abstract

International audienceThe Bay of Biscay (North-East Atlantic) has long been subjected to intense direct and indirect human activities that lead to the excessive degradation and sometimes overexploitation of natural resources. Fisheries management is gradually moving away from single-species assessments to more holistic, multi-species approaches that better respond to the reality of ecosystem processes. Quantitative modelling methods such as Ecopath with Ecosim can be useful tools for planning, implementing and evaluating ecosystem-based fisheries management strategies. The aim of this study was therefore to model the energy fluxes within the food web of this highly pressured ecosystem and to extract practical information required in the diagnosis of ecosystem state/health. A well-described model comprising 30 living and two non-living compartments was successfully constructed with data of local origin, for the Bay of Biscay continental shelf. The same level of aggregation was applied to primary producers, mid-trophic-levels and top-predators boxes. The model was even more general as it encompassed the entire continuum of marine habitats, from benthic to pelagic domains. Output values for most ecosystem attributes indicated a relatively mature and stable ecosystem, with a large proportion of its energy flow originating from detritus. Ecological network analysis also provided evidence that bottom-up processes play a significant role in the population dynamics of upper-trophic-levels and in the global structuring of this marine ecosystem. Finally, a novel metric based on ecosystem production depicted an ecosystem not far from being overexploited. This finding being not entirely consistent over indicators, further analyses based on dynamic simulations are required

Small pelagic fish feeding patterns in relation to food resource variability: an isotopic investigation for Sardina pilchardus and Engraulis encrasicolus from the Bay of Biscay (north-east Atlantic)

“…Stergiou and Karpouzi 2002), and specifically in the Bay of Biscay (i.e. data from Ecopath modelling; Lassalle et al 2011). Moreover, this morphological difference would lead anchovies to be opportunistic and efficient planktivores (James and Probyn 1989) on prey species from the mesozooplankton compartment at least and would confirm that E. encrasicolus is not specialist feeder in the Bay of Biscay area, as already reported for the North and Baltic Seas (Raab et al 2011).…”

“…In particular, European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) fisheries are of major importance in the area (ICES 2010a). No quota currently exists for sardine despite an observed decrease in their catches in this area (OSPAR 2010 role in the population dynamics of upper trophic levels and in the global structuring of this marine ecosystem (Lassalle et al 2011). …”

Trophic ecology of European sardine Sardina pilchardus and European anchovy Engraulis encrasicolus in the Bay of Biscay (north-east Atlantic) inferred from δ13C and δ15N values of fish and identified mesozooplanktonic organisms

“…However, in several cases, anchovies are found to feed at a slightly higher trophic level than sardines (e.g., Stergiou and Karpouzi, 2002), and specifically in the Bay of Biscay (i.e., data from Ecopath modelling; Lassalle et al, 2011), which invalidates the first hypothesis.…”

Trophic ecology of commercial-size meagre, Argyrosomus regius, in the Bay of Biscay (NE Atlantic)★

“…Clupeiform fish stocks support an abundant and diverse top predator community in the Bay of Biscay (Lassalle et al, 2011). Our results suggested that competitive relationships can occur between commercial-size meagre and other predator species such as hake and sea bass, two abundant commercial high trophic level fish in European Atlantic waters (Mahé et al, 2007;Spitz et al, 2013), or common dolphin (Meynier et al, 2008), the most abundant cetacean in the Bay of Biscay (Laran et al, 2017).…”