Regime shift in a coastal marine ecosystem
Jens Kjerulf Petersen1, Jens Würgler Hansen, Martha Brogaard Laursen
1Department of Marine Ecology, National Environmental Research Institute, University of Aarhus, P.O. Box 358, Frederiksborgvej 399, DK-4000 Roskilde, Denmark. jkp@dmu.dk
Summary
A coastal lagoon experienced a regime shift from a turbid, nutrient-stressed state to a clear-water ecosystem due to a small salinity change. This shift, driven by invasive clams, altered food webs and has implications for coastal water management.
Area of Science:
- Ecology
- Environmental Science
- Marine Biology
Background:
- Coastal lagoons are susceptible to regime shifts, altering ecosystem states.
- Nutrient-stressed environments can be particularly vulnerable to small environmental changes.
- Understanding ecosystem dynamics is crucial for effective coastal water management.
Purpose of the Study:
- To demonstrate ecosystem regime shifts in a coastal lagoon.
- To investigate the impact of salinity changes on ecosystem stability.
- To analyze the cascading effects of biological structure changes on food webs.
Main Methods:
- Observational study of Ringkøbing Fjord, Denmark.
- Analysis of salinity changes facilitated by sluice management.
- Assessment of changes in phytoplankton, zooplankton, and benthic vegetation.
- Evaluation of the role of suspension-feeding clams (Mya arenaria) in ecosystem shifts.
Main Results:
- A small increase in salinity triggered a regime shift from a turbid, bottom-up controlled state to a clear-water, top-down controlled state.
- The shift was facilitated by the recruitment and growth of Mya arenaria, leading to increased benthic grazing.
- Changes in dominant organic matter production pathways (pelagic to benthic-pelagic coupling) were observed.
- Phytoplankton composition, zooplankton abundance, benthic vegetation, and waterbird populations were significantly affected.
Conclusions:
- Ecosystem regime shifts can be triggered by small environmental changes in coastal lagoons.
- The invasion and proliferation of suspension-feeding clams can fundamentally alter lagoon ecosystems.
- These shifts have significant implications for coastal water management and environmental legislation.
- Increased water transparency is leading to a recovery of plant coverage in the lagoon.
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