The worldwide crisis of fisheries, which are usually managed on a single species basis, has led to calls for ‘ecosystem management’, along with he development of various ecosystem indicators. The Marine Trophic Index (MTI) and the related Fishing-in-Balance (FiB) index are two such ndicators, which can be used to draw inferences on the sustainability of fisheries, notably those targeting high-t...

Ratio-dependent and prey-dependent models of trophic interactions make very different predictions about the steady-state (equilibrial) properties of ecosystems, such as the response of equilibrium abundance and biomass of organisms in each trophic level to increased primary productivity or nutrient input. Prey-dependent heory predicts alternating positive, negative, and zero responses of trophi...

A model for the bioaccumulation of methyl-mercury in an aquatic ecosystem is described. This model combines predator-prey equations for interactions across three trophic levels with pharmacokinetic equations for toxin elimination at each level. The model considers the inflow and outflow of mercury via tributaries, precipitation, deposition and bacterial methylation to determine the concentratio...

Factors constraining the structure of food webs can be investigated by comparing classes of ecosystems. We find that pelagic ecosystems, those based on one-celled primary producers, have longer food chains than terrestrial ecosystems. Yet pelagic ecosystems have lower primary productivity, contrary to the hypothesis that greater energy flows permit higher trophic levels. We hypothesize that lon...

Food web ecologists have long sought to characterize the trophic niches of animals using stable isotopic analysis. However, distilling trophic position from isotopic composition has been difficult, largely because of the variability associated with trophic discrimination factors (inter-trophic isotopic fractionation and routing). We circumvented much of this variability using compound-specific ...

Understanding species interactions among top marine predators and interactions with their prey can provide important insight into community-level responses to changing prey availability and the role of apex predators as indicators of ecosystem change. On the northeast Newfoundland coast, marine predators rely on capelin (Mallotus villosus), a dominant forage fish, as a food source. Capelin migr...

Studies on the factors determining parasite richness in hosts are typically performed using data compiled for various sets of species from disparate habitats. However, parasite transmission is embedded within local trophic networks, and proper comparisons among host species of the drivers of parasite richness should ideally be conducted among hosts belonging to the same local network. Here, we ...

Coastal marine ecosystems worldwide have undergone such profound transformations from over-fishing that trophic interactions observed today might be artifacts of these changes. We determined whether the trophic level of an endangered seabird, the Marbled Murrelet (Brachyramphus marmoratus), has declined over the past 100 years after the collapse of Pacific sardine (Sardinops sadax) fisheries in...

The mean trophic level of the farmed fish species in the Mediterranean has been increasing. We examined the farming-up hypothesis (i.e., the increase in the production of high-trophic-level species) in the Mediterranean by determining the trophic level of the aquafeeds (i.e., what the fish are fed) of 5 species of farmed marine fishes: common dentex (Dentex dentex), common pandora (Pagellus ery...