Limnetica 38

Macrophytes are key elements for biodiversity in Mediterranean ponds and coastal lagoons. To predict the long-term persistence of aquatic plant populations in a changing environment is essential to understand their phenology, i.e. the timing of ecological processes coupled with environmental factors. Utricularia australis and Stuckenia pectinata (=Potamogeton pectinatus) populations growing in a brackish interdunal pond within the Albufera de València Natural Park were monitored over three years. We describe their life-cycles under shallow conditions and relate them to accumulated heat and radiation. U. australis overwintered as turions; turion germination happened in February at 125-210 growing degree-days (GDD), at a daily mean temperature (DMT) of 10-11 °C, and with 150-220 hours of accumulated sunshine (h Sun). The flowering period started in June (2450 GDD, 26 °C DMT, 1365 h Sun), but only in 2014 and in the sunniest areas of the pond. The turion formation started in early August (3800-4000 GDD, 20-28 °C DMT, 1900-2180 h Sun). A reduction in U. australis biomass and coverage was observed throughout time. S. pectinata exhibited a perennial population restricted to the pond deeper basins. It initiated its life-cycle in late February-early March, mainly by re-sprouting from old stems and roots, vigorously producing new shoots with green leaves (400-440 GDD, 11-12 °C DMT, 300-380 h Sun). In early May, the production of the first spikes was detected (840-1045 GDD, 17-18 °C DMT, 820-900 h Sun). By mid-June, fertilization was complete and drupelet growth began (1430-1800 GDD, 20-23 °C DMT, 1190-1230 h Sun). Increased salinity and competition with charophytes developed in the pond, negatively affected the fertility and abundance dynamics of S. pectinata. U. australis performance declined with the reduction in free-water surface due to the expansion of helophytes, mainly cattails. The S. pectinata life-cycle in this pond fits in with the latitudinal pattern of a prolonged life-cycle with a delayed reproduction for southern populations. The restoration of degraded or destroyed aquatic ecosystems is a turning point for local populations to recover, but some management of the restored waterbodies is required to guarantee the preservation of peculiar and endangered species. In situ continuous monitoring of water temperature, and other relevant variables for submerged vegetation (such as light availability and salinity), is needed to have a more precise image of the environmental factor values required to pass from one phenological event to another, and for a better comparison among populations from different origins.