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

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.

Global Systematic Review of Methodological Approaches to Analyze Coastal Shelf Food Webs

“…Coastal systems are energetically supported by a variety of sources, including local benthic or pelagic producers, as well as allochthonous organic matter which may originate either from land via freshwater run-off or from the open sea through tidal currents and upwellings (Nielsen and Navarrete, 2004;Carlier et al, 2015;Christianen et al, 2017;Meunier et al, 2017). Moreover, the proportional contribution of the different energy sources to coastal shelf food webs may also be affected by several human-induced drivers, such as coastal development, seabed disturbance, eutrophication, and changes in river flow (Tewfik et al, 2005;Al-Habsi et al, 2008;Christianen et al, 2017;Hemraj et al, 2017). Today, it is clear that long term anthropogenic activities can cause major shifts in coastal shelf food web structure, which lead to simplified communities (Tewfik et al, 2005).…”

“…A dynamic equilibrium takes place among trophic levels, severely affected by environmental drivers (Menge and Sutherland, 1987;Hunt and McKinnell, 2006). This is why holistic assessments of food webs are needed (Lindeman, 1942;Odum et al, 1971;Libralato et al, 2014) to investigate their dynamics and the potential for human-induced modifications, or even regime shifts through trophic cascades (Pace et al, 1999;Polis et al, 2000), due to e.g., fisheries (Pauly et al, 1998;Shannon et al, 2014), eutrophication (Armitage and Fourqurean, 2009), climate change (Ainsworth et al, 2011), pollution (Young et al, 1982), habitat alteration (Tallis, 2009;Bishop et al, 2010;Hemraj et al, 2017), and alien species (Corrales et al, 2017a).…”

Effects and prediction of nonpoint source pollution on the structure of aquatic food webs

“…Changes in the structure of the food web have important impacts on ecosystem functions and ecological value (Hemraj et al, 2017; Robson et al, 2017). In order to further quantitatively analyse the influence of important factors of nonpoint source pollution on the level of food web structure, the overall characteristics of the food web structure are comprehensively evaluated through the food web structure level index model (Zhao et al, 2019).…”

“…According to the First National Survey of Pollution Sources Bulletin of China, rural nonpoint source pollution includes approximately half of the total water pollution, accounting for 57% of the total N and 67% of the total P. Nonpoint source pollution has become the principal source for water pollution in China and severely damaged aquatic ecosystems. It resulted in changes in water quality factors that affect the hierarchy and structure of the ecosystem (Zhao et al, 2018) and the integrity of the food web (Carvalho, Williner, Ciri, Vaccari, & Collins, 2016), deeply influencing ecosystem functions and services (Hemraj, Hossain, Ye, Qin, & Leterme, 2017; Robson et al, 2017). However, there is currently a lack of quantitative research on the impact of nonpoint source pollution on the structure of aquatic food webs.…”

The dynamics of the plankton community on Lake Siombak, a tropical tidal lake in North Sumatra, Indonesia

“…This nutrient enrichment creates an environmental gradient changing the chemical and biological properties of the lagoon directly or indirectly (Mentzafou and Dimitriou 2019;Pérez-Ruzafa et al 2019). This will result in high biomass accumulation and drastic changes in the structure of the plankton food network and ecosystem function (Hemraj et al 2017;Bueno-Pardo et al 2018;Cutrim et al 2019;Pérez-Ruzafa et al 2019;Pérez-Ruzafa et al 2020).…”