Functional Effects of Parasites on Food Web Properties during the Spring Diatom Bloom in Lake Pavin: A Linear Inverse Modeling Analysis

This study is the first assessment of the quantitative impact of parasitic chytrids on a planktonic food web. We used a carbon-based food web model of Lake Pavin (Massif Central, France) to investigate the effects of chytrids during the spring diatom bloom by developing models with and without chytrids. Linear inverse modelling procedures were employed to estimate undetermined flows in the lake. The Monte Carlo Markov chain linear inverse modelling procedure provided estimates of the ranges of model-derived fluxes. Model results support recent theories on the probable impact of parasites on food web function. In the lake, during spring, when ‘inedible’ algae (unexploited by planktonic herbivores) were the dominant primary producers, the epidemic growth of chytrids significantly reduced the sedimentation loss of algal carbon to the detritus pool through the production of grazer-exploitable zoospores. We also review some theories about the potential influence of parasites on ecological network properties and argue that parasitism contributes to longer carbon path lengths, higher levels of activity and specialization, and lower recycling. Considering the “structural asymmetry” hypothesis as a stabilizing pattern, chytrids should contribute to the stability of aquatic food webs

A toolbox to evaluate data reliability for whole-ecosystem models

International audienceEcosystem models are simplifications of reality and their application for ecosystem-based management requires standard validation. The main aim of this study was to propose to modellers an operational and easy-to-use toolbox checking for data reliability

Inverse Modeling in Modern Ecology and Application to Coastal Ecosystems

International audienceQuantitative estimates of energy or material flows within food webs are increasingly viewed as essential to progress on a number of questions in ecosystem science. Inverse analysis has been used since the 1980s to estimate all flows within plankton food webs originally based on incomplete information. Its application to many aquatic environments, including the coastal zone, has led to a variety of methodological improvements. This chapter explains the methodology of inverse modeling and illustrates its application in modern ecosystems ecology. This relatively new approach also provides rigorous statistical comparisons of food web properties across ecosystems. © 2011 Elsevier Inc. All rights reserved

Effet de changements d'ordre climatique sur le réseau trophique du Golfe de Gascogne : un focus sur les espèces dominantes de poisson

International audienceAlthough the Bay of Biscay is an ecoregion with a long history of fisheries exploitation, it is also influenced by climate change that affects ecosystem structure and trophodynamics. In this study, using a linear inverse model based on a Monte Carlo-Markov Chain approach (LIM-MCMC) and an Ecological Network Analysis (ENA), we assess the trophic status of this region under different scenarios of climate change (IPCC scenarios A1B, A2 and B2)). More precisely, we will estimate the potential consequences of climate-driven alterations of fish compartments on (1) other trophic compartments, and (2) on the food-web structural properties. A first set of scenarios of climate-driven alterations of fish compartments came from a multispecies individual-based model (OSMOSE) applied in the Bay of Biscay. The OSMOSE model estimates the biomass dynamics of main exploited fish species together with associated processes (e.g. growth, respiration, mortality) from the outputs of the biogeochemical model ROMS-N2P2Z2D2 (i.e., predator/prey possibility of co-occurrence and compatibility between predators’ and preys’ sizes). A second set of climate-driven alterations of fish compartments is provided by the Non-Parametric Probabilistic Ecological Niche (NPPEN) model, predicting probabilities of occurrence based on species ecological niches sensu Hutchinson from key environmental factors. The coupling of LIM-MCMC with ENA allows statistical comparisons of food web properties to be investigated

Quantitative food web modeling unravels the importance of the microphytobenthos-meiofauna pathway for a high trophic transfer by meiofauna in soft-bottom intertidal food webs

Publisher: Elsevier B.V.International audienceMeiofauna are known to have an important role on many ecological processes, although, their role in food web dynamics is often poorly understood, partially as they have been an overlooked and under sampled organism group. Here, we used quantitative food web modeling to evaluate the trophic relationship between meiofauna and their food sources and how meiofauna can mediate the carbon flow to higher trophic levels in five contrasting soft-bottom intertidal habitats (including seagrass beds, mudflats and sandflats). Carbon flow networks were constructed using the linear inverse model-Markov chain Monte Carlo technique, with increased resolution of the meiofauna compartments (i.e. biomass and feeding ecology of the different trophic groups of meiofauna) compared to most previous modeling studies. These models highlighted that the flows between the highly productive microphytobenthos and the meiofauna compartments play an important role in transferring carbon to the higher trophic levels, typically more efficiently so than macrofauna. The pathway from microphytobenthos to meiofauna represented the largest flow in all habitats and resulted in high production of meiofauna independent of habitat. All trophic groups of meiofauna, except for selective deposit feeders, had a very high dependency on microphytobenthos. Selective deposit feeders relied instead on a wider range of food sources, with varying contributions of bacteria, microphytobenthos and sediment organic matter. Ecological network analyses (e.g. cycling, throughput and ascendency) of the modeled systems highlighted the close positive relationship between the food web efficiency and the assimilation of high-quality food sources by primary consumers, e.g. meiofauna and macrofauna. Large proportions of these flows can be attributed to trophic groups of meiofauna. The sensitivity of the network properties to the representation of meiofauna in the models leads to recommending a greater attention in ecological data monitoring and integrating meiofauna into food web models. © 2020 Elsevier B.V

Potential combined impacts of climate change and non-indigenous species arrivals on Bay of Biscay trophic network structure and functioning

International audienceThe consequences of climate change for marine organisms are now well-known, and include metabolism and behavior modification, distribution area shifts and changes in the community. In the Bay of Biscay, the potential environmental niches of subtropical non-indigenous species (NIS) are projected to expand as a response to sea temperature rise by the mid-century under the RCP8.5 climate change scenario. In this context, this study aims to project the combined effects of changes in indigenous species distribution and metabolism and NIS arrivals on the functioning of the Bay of Biscay trophic network. To do this, we created six different Ecopath food web models: a “current situation” trophic model (2007–2016) and five “future” trophic models. The latter five models included various NIS biomass combinations to reflect different potential scenarios of NIS arrivals. For each model, eight Ecological Network Analysis (ENA) indices were calculated, describing the properties of the food web resulting from the sum of interactions between organisms. Our results illustrate that rising temperature increases the quantity of energy passing through the system due to increased productivity. A decrease in the biomass of some trophic groups due to the reduction of their potential environmental niches also leads to changes in the structure of the trophic network. The arrival of NIS is projected to change the fate of organic matter within the ecosystem, with higher cycling, relative ascendency, and a chain-like food web. It could also cause new trophic interactions that could lead to competition and thus modify the food-web structure, with lower omnivory and higher detritivory. The combined impacts (increasing temperatures and NIS arrivals) could lower the resilience and resistance of the system

Contrasting pelagic ecosystem functioning in eastern and western Baffin Bay revealed by trophic network modeling

International audienc