Estuary hydrogeomorphology affects carbon sources supporting aquatic consumers within and among ecological guilds

Abstract

The relative importance of carbon sources supporting aquatic food webs within and among estuaries may be influenced by factors that affect relative availability of autotrophic carbon sources, as well as movement of individuals among marine, estuarine and freshwater zones. We used stable isotopes of carbon and nitrogen to examine (1) the relative importance of carbon sources supporting estuarine consumers among estuaries with different hydrogeomorphic characteristics, (2) stable isotope signatures of consumer ecological guilds defined by dependence on estuarine habitats and residence time, and (3) if patterns in stable isotope signatures of ecological guilds repeat across estuaries with distinct hydrogeomorphological features. At the assemblage level, consumer carbon isotope signatures reflected the consumption of locally abundant primary production sources and differed across estuary types (choked lagoon, coastal river). Consumer ecological guilds differed in d 13 C within sites, and the same trend repeated across sites but with differing magnitudes. This variation is attributed to movement and residence patterns in addition to differences in the relative abundances of autotrophic sources across sites. Although within-estuary variation in consumer resource use is to be expected, estuarine food webs may be broadly classified according to landscapescale hydrogeomorphic factors that allow an initial prediction of the relative importance of carbon sources to secondary production. Predictions may be refined at the species level using knowledge of habitat use and residence time. Such predictions are useful as a starting point for poorly studied regions such as ours in southern Brazil, as well as for globalscale analyses of patterns in estuarine food webs.

Trophic segregation of a fish assemblage along lateral depth gradients in a subtropical coastal lagoon revealed by stable isotope analyses

“…Food webs are constructed in such a way that energy channels based on different basal food resources are coupled by higher trophic categories (Rooney et al ., ). Although consumers in aquatic food webs typically rely on multiple resource pathways and functional groups may differ in their resource use (Alfaro et al ., ), predictions may be made regarding dominant energy sources supporting consumers at the level of the entire assemblage (Hoeinghaus et al ., ). The present lateral gradient conceptual diagrams for fish basal food source use in different salinity regions confirmed that consumer reliance on multiple resource pathways is more marked in shallow areas.…”

“…In the deep areas of the coastal lagoon, SOM was an important carbon source for fishes, especially the zoobenthivores, whereas in shallow locations its importance as a primary food source for fishes was mainly shared with or even substituted by macrophytes. The high proportion of lower elevation littoral and larger mixohaline zones in Patos Lagoon estuary, when compared with adjacent subtropical estuaries, favours the presence of typical salt marsh vegetation, such as the genus Spartina (Costa, ; Hoeinghaus et al ., ). Besides playing an ecological role as a refuge from predators, emergent and submerged macrophytes also represent a richer feeding habitat (Halpin, ; Teixeira‐de‐Mello et al ., ; Whitley & Bollens, ).…”

Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

“…The relative importance of these sources depends partially on the availability of terrestrial and aquatic material (Polis et al 1997, Bouillon et al 2004. While the availability of autochthonous material is regulated by physical and biological factors such as light (e.g., Boston and Hill 1991) and nutrient availability (Flindt et al 1999), turbidity, water depth (e.g., Krause-Jensen and Sand-Jensen 1998) and substrate type (Rizzo and Wetze 1985), the availability of terrestrial material depends on a different set of factors such as hydrodynamics and geomorphology and landscape characteristics of the catchment (Polis et al 1997, Hoeinghaus et al 2011.…”

Stable isotopes reveal temporal and between-habitat changes in trophic pathways in a southwestern Atlantic estuary

“…Fish and decapod macrocrustaceans were collected with beach seine hauls, and infaunal organisms were collected with plastic cores (10 cm diameter, 20 cm depth, 0.0078 m 2 area) and retained on 500 µm mesh nets. All samples were stored in sealed plastic bags on ice and transported to the laboratory, where they were kept frozen and later processed (Garcia et al 2007, Hoeinghaus et al 2011.…”

“…Rather, most studies constitute 'snapshots' of patterns associated with between-site differences (e.g. Connolly et al 2005, Pasquaud et al 2008, Hoeinghaus et al 2011 or changes along salinity gradients (e.g. Garcia et al 2007, França et al 2011.…”