Chapter 12 - Structurally Dynamic Model and Ecological Indicators to detect the crayfish invasion in a lake ecosystem

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We developed a structurally dynamic model of Lake Chozas, a small shallow water body in Leon (northwest Spain). The model simulated seasonal dynamics of phosphorus concentrations in major components of the lake’s ecological network before and after 1997, the year when an invasive the allochthonous crustascean, the Louisiana red swamp crayfish (Procambarus clarkii), was introduced into the lake. The shift from clean to turbid phase, due to grazing by crayfish on submerged vegetation, caused a gradual decrease in eco-exergy, reflecting an increase in entropy. Moreover, we tested the hypotheses about the recovery of the indigenous community and water quality, when all the crayfish were removed. The recovery of Lake Chozas after the biological invasion was observed when phytoplankton dominated at total phosphorus about ≥ 200–250 mg TP/m3, and submerged vegetation returned at total phosphorus <100 mg TP/m3. To conclude the analysis, we studied health status of Lake Chozas before and after the biological invasion, compared to Lake Sentiz (a similar water body in the same district), by the joint use of different but correlated ecological indicators, supplementing the values obtained by monitoring campaigns. The joint application of different ecological indicators gives a more effective and comprehensive description of the ecosystem health status than any one considered alone.