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Estuarine consumers utilize marine, estuarine and terrestrial organic matter and provide connectivity among these food webs
Citation:
Dias, E., P. Morais, A. Cotter, C. Antunes, AND J. Hoffman. Estuarine consumers utilize marine, estuarine and terrestrial organic matter and provide connectivity among these food webs. MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 554:21-34, (2016).
Impact/Purpose:
The study demonstrates the ability of estuarine primary consumers to utilize the external subsidies from terrestrial and marine environments, thereby linking terrestrial and marine ecosystems. The study is relevant to assessments of coastal ecosystem condition because it demonstrates how flows of materials (nutrients, energy) across the land-sea interface influence fundamental characteristics of estuarine ecosystems.
Description:
The flux of organic matter (OM) across ecosystem boundaries can influence estuarine food web dynamics and productivity. However, this process is seldom investigated taking into account all the adjacent ecosystems (e.g. ocean, river, land) and different hydrological settings (i.e. river discharge). Therefore, we aimed to quantify the contribution of autochthonous and allochthonous OM to the lower food web of a temperate estuary under different river discharge conditions. We hypothesized that the contribution of terrestrial and riverine allochthonous OM would be greatest during periods of high river discharge, whereas the contribution of autochthonous and marine-derived OM would be greatest under low river discharge. The carbon (C) and nitrogen (N) stable isotope ratios of pelagic (zooplankton) and benthic (Corbicula fluminea) primary consumers indicate they relied on a mixture of autochthonous and allochthonous OM, including terrestrial-derived OM. Unexpectedly, the highest contribution of terrestrial-derived OM to the estuarine food web was observed during low river discharge periods (up to 70%), but in a summer period that succeeded a large winter flood. As hypothesized, the contribution of marine-derived OM was higher during low river discharge periods (up to 88%), and was restricted to the first kilometers of the estuary. Concomitantly, the contribution of phytoplankton to primary consumers was the highest observed (up to 91%). Further, both pelagic and benthic consumers also relied on benthic C (i.e., sediment OM and microphytobenthos). The study demonstrates that primary consumers enhance estuarine ecosystem connectivity by utilizing subsidies of terrestrial and marine origin, and also between estuarine habitats through reliance on pelagic and benthic OM.
