TROPHIC NETWORK MODELS AND PREDICTION OF TOXIC SUBSTANCES ACCUMULATION IN FOOD WEBS

The term food web or trophic network defines a set of interconnected food chains by which energy and materials circulate within an ecosystem. The classical food web could be divided into two broad categories: the grazing web, which typically begins with green plants, algae, or photosynthesizing plankton, and the detrital web, which begins with organic debris. In a grazing web, materials typically pass from plants to herbivores to flesh eaters. In a detrital web, materials pass from plant and animal matter to decomposers as fungi and bacteria, then to detritivores, and then to their predators. In water ecosystems, the classical food web is represented by the planktonic and benthic food webs, which are interconnected. Additionally, the “microbial loop” represents an alternative pathway of carbon flow that leads from bacteria to protozoa to metazoa, with dissolved organic matter (DOM) being utilized as substrate by the bacteria, which include nanoplankton (2–20 μm in size) and picoplankton (0.2–2 μm in size). Food web models are generally built by reconstructing and quantifying the ecosystem trophic transfer network. This type of ecological model has been widely used for many applications, including fishery and stock management, eutrophication studies, and tracing bioaccumulation processes in water ecosystems. In many cases, once built, particular food web models could used for different applications such as for modeling both eutrophication and bioaccumulation (Koelmans et al., 2001), which often appear to be interrelated processes (Schaanning et al., 1996; Gourlay et al., 2005). The recent development of the ECOPATH project for dynamic simulation and the introduction of ECOSIM and ECOTRACE routines (Christensen and Walters, 2004) provides the opportunity to use a number of trophic models already developed for the modeling of persistent pollutants bioaccumulation in the trophic food webs.