Changes in food web structure of fish assemblages along a river-to-ocean transect of a coastal subtropical system

Abstract

There is an urgent need to understand how food web structure changes along environmental gradients. In this study we investigated changes in trophic organisation and the relative importance of autotrophic sources sustaining fish assemblages along a transect from river to ocean. In order to address these topics, we analysed fish stomach contents and isotopic composition of consumers and food sources. The findings revealed a greater number of autotrophic sources sustaining fish assemblages in the continental systems (especially in the river) than in the adjacent marine system. Bipartite networks depicting trophic relationships between fish and prey also changed along the transect, showing comparatively higher complexity in the estuary. These findings could be explained by the greater number of food web components (autotrophic sources, fish trophic guilds and prey) associated with pelagic and benthic food chains within the estuary compared with the adjacent systems studied. The findings of this study highlight the need to take into account river-to-ocean changes in food web structure of fish assemblages in management plans to mitigate human impacts in coastal systems.

Long-Term Spatiotemporal Variation in the Juvenile Fish Assemblage of the Tramandaí River Estuary (29°S) and Adjacent Coast in Southern Brazil

“…Habitat heterogeneity should contribute to the greater richness of species in TRE, and also to other environments, especially coastal lagoons and other estuaries (Petry et al, 2016). These findings could be explained by the greater number of food web components (autotrophic sources, fishes trophic guilds and prey) associated with pelagic and benthic food chains within the estuary in comparison to the adjacent systems studied (Garcia et al, 2018b).…”

“…The estuarine regions in southern Brazil present a greater variety of habitats compared to adjacent coastal zones (Ramos and Vieira, 2001;Odebrecht et al, 2017). With regard to the TRE and AC complex, Garcia et al (2018b) shows that fish assemblages in continental systems are sustained by a greater number of autotrophic sources than in the adjacent marine systems. Habitat heterogeneity should contribute to the greater richness of species in TRE, and also to other environments, especially coastal lagoons and other estuaries (Petry et al, 2016).…”

“…Juvenile M. liza showed higher abundance in the estuarine environment (54%) and M. curema in the marine environment (50%). Although salinity preference seems to be the main factor that segregate the juveniles of these two species, temperature is the variable that best separates them (Vieira, 1991;Garcia et al, 2018b;Mai et al, 2018). Adults of both species spawn in the marine environment and juveniles use the coastal region and estuaries as nurseries (Vieira, 1991;Mai et al, 2018).…”

“…Currently, limited information has been compiled about the TRE and the adjacent coast (AC- Ramos and Vieira, 2001;Malabarba et al, 2013;Garcia et al, 2018b;Santos et al, 2018). However, the Laboratory of Ichthyology at the Federal University of Rio Grande (FURG) has a series of unpublished long-term data on the TRE.…”

Trophic structure of frog assemblages in coastal habitats in southern Brazil

“…Community trophic structure often changes in response to spatial and temporal variation in environmental conditions (Winemiller 1990;Polis et al 1996;Correa & Winemiller 2014;Garcia et al 2017). Spatial changes in trophic structure across ecosystems may occur due to variation in factors such as composition and diversity of primary producers and consumers, primary productivity, inter-and intraspecific interactions and various abiotic environmental drivers (Polis et al 1996;Catry et al 2016;Garcia et al 2019). Greater diversity of primary producers generally yields higher net primary production, even in oligotrophic systems (Tilman 1988;Tilman et al 2014).…”