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The role of dragonflies as the peak predators and indicators of the health of the Mediterranean ponds

Mediterranean freshwater ponds are specific, sometimes man-made freshwater habitats on islands and coast. Since they are mainly isolated freshwater habitats in the arid and marine environment, they represent precious habitats with high freshwater species diversity. They are sensitive to weather and detrimental human effects due to their properties (e.g. small volume, low depth, karst base, proximity to the sea). These ponds undergo washing of nutrients, toxins and soil from surrounding areas, salinization, and water level fluctuations and are often semi-permanent or temporary. Benthic macroinvertebrates are sentinel indicators of water ecological state as well as changes therein. Thus, across the Dugi otok island macroinvertebrates in 10 ponds were sampled. Benthic community was comprised of 41 taxa of which the top predators, dragonflies, were dominant, in biomass and in abundance. Therefore, further research was focused on dragonflies, specifically genera Sympetrum and Anax. Their presence differed among ponds, depending on the macrophyte coverage, salinity and the dragonfly prey size in the pond. Sympetrum fonscolombei was the most abundant species, with the highest biomass and thus it was the best choice for life cycle study. Head capsule width was measured with a digital micrometer and thirteen instars were distinguished and separated. Taking into account the broad taxonomic structure of the benthic community, its trophic composition, and standing stock biomass of the top predator these habitats (although in a rather high trophic state) indicated healthy and stabile ecosystems. Hence, we encourage further protection and research of these curious and precious habitats.

macroinvertebrates, trophic composition, Mediterranean ponds

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