The Compositional and Functional Diversity of a Mediterranean Urban Lake's Fish Fauna over the Past 120 Years

This study examines the compositional (taxonomic) and functional diversity changes in the fish fauna of a Mediterranean urban lake (Lake Kastoria) over a period of 12 decades (1900-2020, as of 2022). Moreover, the current status (2010 and 2022) of the fish fauna is assessed along with the lake's ecological quality. Intentional or accidental species introductions resulted in significant compositional changes in the lake's fish fauna. The functional richness among the assemblages from 1900 and 2020 was increased due to species introductions, resulting in a peak of functional dissimilarity in 1990, when most introductions took place. However, the functional dissimilarity measures revealed that there have been moderate changes in groups of the functional traits which may be indicative of high species competition. The lake's open waters are dominated by Rutilus rutilus and the introduced species Perca fluviatilis and Lepomis gibbosus. The estimated ecological quality was higher in 2022 than in 2010, categorizing the lake as having "Moderate" quality and providing an upgrade from its earlier 'Poor" condition. This positive shift is attributed in part to the burgeoning population of Perca fluviatilis, as evidenced by increased catch rates. The species' resurgence may be linked to enhancements in the lake's physicochemical parameters, potentially facilitated by more effective treatment of urban wastes. The study underscores the complex interplay between species introductions, functional diversity, and ecological quality in the urban Lake Kastoria, highlighting the need for continued monitoring and management efforts to sustainably preserve and enhance the biodiversity and ecological integrity of urban aquatic ecosystems.