MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12356

Winter river discharge may affect summer estuarine jellyfish blooms

Katherine Amorim, Ramona M. Mattmüller, María Algueró-Muñiz, Cédric L. Meunier, Santiago Alvarez-Fernandez, Maarten Boersma, Pedro Morais, Maria A. Teodósio*

*Email: mchichar@ualg.pt

ABSTRACT: Dams alter the natural dynamics of river inflow which disrupt biological processes in downstream ecosystems, as observed in the Guadiana estuary (SW Iberian Peninsula, Europe). Here, significant inter-annual fluctuations in the densities of jellyfish occur during summer, likely due to changes in winter river discharge. So, this study aims to quantify the relationship of winter river inflow with the abundance of jellyfish in the Guadiana estuary. Also, the budding and growth of Aurelia aurita polyps of one of the bloom forming species present in the estuary, were determined at different combinations of constant temperature and salinity. The response of polyps and ephyrae to short-term low salinity pulses was also quantified. Maximum winter river discharge and maximum abundance of estuarine medusa (bloom indicator) showed a significant negative correlation. In the constant conditions, polyps increased mortality when water temperature was higher than 23°C and salinity lower than 23, and died when exposed to a short-term low salinity pulse (≤3). Polyp budding and feeding rates, submitted to those freshets decreased 69% and 32% when salinity reached values as low as 10. Ephyrae died when salinity was lower than 10, but feeding rates reduced by 88% when salinity was 17 in comparison to full marine conditions. In conclusion, winter freshwater discharge may regulate the strength of estuarine jellyfish blooms, impairing the survival or condition of polyps and ephyrae during late winter or early spring. River basin managers must consider the prescription of freshets to prevent jellyfish blooms from disrupting ecosystem services (e.g., fisheries, tourism).