Mass balanced models of the food web in three areas along a gradient of eutrophication symptoms in the south arm of the Mondego estuary (Portugal)

Abstract

EutrophicationTrophic structure a b s t r a c t Three Ecopath with Ecosim models were constructed to represent the eutrophication gradient along the south arm of the Mondego estuary (Portugal). Sampling was conducted in three areas representative of different environmental situations along the gradient: (a) a non-eutrophic area (Zostera noltii meadows), (b) an intermediate eutrophic area (macrophyte absent, although residual roots can still be found in the sediment, and the occasional formation of abundant macroalgae mats) and (c) a strongly eutrophic area (macrophyte community totally absent for at least a decade and strong, regularly occurring, blooms of Ulva spp.). Field, laboratory and literature information were used to construct the models, as well as empirical ecological knowledge gained from years of work on this system. Approximately 76 trophic groups (e.g. Phytoplankton and Zooplankton species), species and genera were included. These species were grouped into 43, 36 and 34 model groups for Zostera sp. meadows, intermediate eutrophic area and strongly eutrophic area, respectively. The groups were arranged by trophic similarity and habitat preferences; special distinction is given to macrofauna. Biomass, production, consumption, and diet are among the parameters used to describe each group. The sum of consumptions, exports, respiration, production, flow to detritus, total system throughput and annual rate of net primary production was always higher in the Zostera sp. meadows, followed by the strongly eutrophic area and, finally, by the intermediate eutrophic area.

Trophic flow structure of a neotropical estuary in northeastern Brazil and the comparison of ecosystem model indicators of estuaries

“…where Bi is the biomass of group (i); PBi is the production/biomass ratio of (i), which is equal to total mortality (Z) or natural mortality (M) (Allen, 1971); EEi is the ecotrophic efficiency of (i), which varies from 0 to 1 and represents the part of the production of the group that is transferred to higher trophic levels and/or removed by fishing; Bj is the biomass of the predators (j); QBj is the food consumption per unit of biomass of the predators (j); DCji is the fraction (%) of (i) in the diet of (j); EXi is the export of (i) and refers to the biomass that is caught by fishing and/or migrates to other environments. In this case, as for other Ecopath models (Coll et al, 2006;Han et al, 2016;Patrício and Marques, 2006), we considered migration to be equal to immigration, given the difficulty of estimating the movements of individuals.…”

“…However, we delimited the modeled area to focus on the "wet" part of the estuary, 1.7 km 2 , where most of the interactions among the aquatic compartments occur. In the absence of information on the movement of organisms in/from the continental part of the river or in/from the adjacent marine area, we neglected any immigration/emigration processes and biomass accumulations (Coll et al, 2006), and an assumption of no net migration was presumed here, as it is in other Ecopath models (Coll et al, 2006;Han et al, 2016;Patrício and Marques, 2006).…”

Estuarine production of resident and nursery fish species: Conditioning by drought events?

“…In fact, production estimates integrate the influence of numerous biotic variables and environmental conditions affecting individual growth and population mortality (Cusson and Bourget, 2005;Dolbeth et al, 2005). Therefore, production studies have been used to assess the impacts of natural and anthropogenic stressors Dolbeth et al, 2005Dolbeth et al, , 2007b, in ecosystem modelling studies (energy budgets and flows, Gamito and Erzini, 2005;Patrício and Marques, 2006), and for fish assemblages have been used more frequently to assess the potential yields for fishery species (Houde and Rutherford, 1993;Wilson, 2002;Pombo et al, 2007).…”

Opportunistic macroalgae metrics for transitional waters. Testing tools to assess ecological quality status in Portugal

“…Through time such modifications induced the emergence of a new selected trophic structure, which has been profusely analysed in abundant literature (e.g. Marques et al, 2003;Cardoso et al, 2004;Patrício and Marques, 2006). Nevertheless, at least until a certain extent, this trend apparently reversed from 1998 after the implementation in late 1997, of experimental mitigation measures consisting of a decrease in the freshwater discharge proceeding from the Pranto River sluice as a consequence of a limited re-establishment of the communication between the two arms.…”