Hydrologic pulsing promotes spatial connectivity and food web subsidies in a subtropical coastal ecosystem

Abstract

Resource pulsing is a widespread phenomenon, but its effects on ecosystem dynamics are often difficult to predict. Hydrological pulsing, in particular, is known to influence the structure and dynamics of fluvial and coastal ecosystems, but little information is available about its effects on trophic connectivity between wetlands and estuaries. We investigated the hypothesis that hydrologic pulsing drives 1-way trophic subsidies (e.g. suspended organic matter and freshwater fish) from wetland to estuary. Our study system is a coastal lagoon with an ephemeral mouth that, when closed, stores freshwater as a sustained flood pulse that is subsequently released when a connection with the sea is reestablished. We monitored isotopic composition of consumers and food sources over the course of an entire flood pulse to infer trophic linkages and spatial subsidies. Before the flood peak (April and May), freshwater and estuarine zones were largely dependent on local primary production sources (seston and C 3 plants vs. C 4 plants and microphytobenthos, respectively), essentially functioning as disconnected compartments. A sustained pulse of freshwater inflow (June to August) induced greater habitat connectivity and a net flow of biomass and energy from the freshwater zone into the estuarine zone. The opening of the lagoon outlet channel abruptly terminated the flood pulse and reduced freshwater subsidies to estuarine consumers, and both zones returned to dependence on autochthonous production. Our findings contribute to current concerns that artificial opening of sandbars in coastal lagoons alters natural ecological dynamics with significant effects on biodiversity and ecosystem processes.

Trophic structure of frog assemblages in coastal habitats in southern Brazil

“…Other studies have revealed multiple primary producers supporting food webs of coastal ecosystems, including other wetlands in southern Brazil (e.g. Garcia et al 2017). For example, Catry et al (2016) found that productive coastal ecosystems with diverse basal production sources were associated with relatively low trophic redundancy among consumers.…”

“…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).…”

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

“…However, the beach seine is a good sampling device for regular low-cost projects (Vieira, 2006;Ceni and Vieira, 2013) and we strongly recommend this gear to be used in the future so comparisons can be made with past data that have been gathered using this seine. This is illustrated in the long term studies of the Patos Lagoon estuary and adjacent area where this seine have been employed monthly since 1996 (Vieira et al, 2010;Garcia et al, 2017).…”

“…Ecological studies of the Patos Lagoon estuary show that increased precipitation during El Niño events change the salinity regime due to increased runoff of continental water. As a consequence there is an increase in the number of freshwater fish species in the estuary (Garcia and Vieira, 2001;Garcia et al, 2004Garcia et al, , 2017Possamai et al, 2018). Freshwater species are much less frequent in the coastal region adjacent to estuaries (Ramos and Vieira, 2001;Monteiro-Neto et al, 2003;Lima and Vieira, 2009;Rodrigues et al, 2014), but the general abundance and diversity of the fish fauna in the marine coastal region are also affected by freshwater runoff coming from the estuary (Martins et al, 2015).…”

Trophic Ecology of Two Sympatric Frogs with Contrasting Morphology and Habitat Use in a Subtropical Wetland

“…Isotopic spaces occupied by P. minuta and S. squalirostris overlapped broadly during the cold/wet period when higher rainfall produced a hydrologic pulse that connected aquatic habitats in the wetland (Garcia et al 2017). Hydrologic connectivity promotes entry of terrestrial invertebrates, vegetation, and riparian detritus into aquatic habitats (Rezende and Mazzoni 2005).…”