The effect of two extreme climate events on coastal meiofaunal communities and ecosystem health

Two consecutive extreme storms, "Daniel" (4-8 September 2023) and "Elias" (25-28 September 2023), struck the region of Thessaly resulting in flash floods, with Pagasitikos gulf being the main recipient. Eight sites were selected based on the degree of intensity of disturbance, with sample collection taking place immediately, 6 months and a year following the events. The first 2 cm of sediment were analyzed in terms of meiofauna, nematodes and sediment characteristics. Physical (temperature, salinity) and chemical (pH, dissolved oxygen, redox potential, nutrients) water quality parameters were, also, measured. Indicator species analysis (ISA) and nematode functional traits were used to assess the ecosystemic quality. The environmental parameters varied with time but not with disturbance intensity. The results indicated differences in meiofaunal diversity and abundance patterns between high and low intensities. Sediment redox was the most significant environmental factor affecting the meiofaunal and nematode communities. Nematode diversity and c-p scores were characteristic of recolonization, with higher diversities observed immediately after the events. Persisting genera in high intensity sites were initially absent. ISA indicated that almost all sites were associated with tolerant genera, however single groups of sites were also associated with sensitive ones, while the use of functional traits determined that after one year almost all sites attained moderate levels of ecosystemic quality. Ecosystemic restoration was delayed for high intensity sites. The rate of recolonization was related to intensity of disturbance, while the required time for meiofaunal community to reach stability was longer than expected, suggesting less tolerance than previously thought.