Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation

A Hossain,Qifeng Ye,Sophie C Leterme,Jian G Qin,Deevesh A Hemraj

doi:10.1038/srep44441

A Hossain, Qifeng Ye + Show 3 more

Open Access

https://doi.org/10.1038/srep44441

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Abstract

Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong.

Highlights

Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states
Our results show that the high peak and low trough in freshwater flow through the barrages is highly influential on the changes in water quality
High flow contributes to nitrogen loading, especially in the North lagoon

Summary

Introduction

Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. Some of the most important modifications have involved bottom-up or top-down regulated trophic cascades, significantly influencing trophic interactions in food webs[2,3] Such alterations are often followed by non-equilibrium and degradation (i.e., system recovery is slower than the frequency of disturbance) in ecosystems, creating instability in ecosystem state[4,5]. The Coorong is a shallow saline coastal lagoon of approximately 110 km long which provides a range of commercial and recreational ecosystem services[17] It is situated at the end of Australia’s largest river basin, the Murray-Darling basin, and is part of a Ramsar listed wetland area (Ramsar Convention on Wetlands, an intergovernmental treaty for the conservation and adequate use of wetlands; www.ramsar.org) called the Coorong, Lower Lakes and Murray Mouth region. Of the Murray River and the main source of freshwater is through barrages built to prevent seawater intrusion into the lakes and to regulate freshwater input into the Coorong[18,19]

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