A warming decade unveils changes in the chaetognath Parasagitta friderici and appendicularian Oikopleura dioica abundance in a coastal system of the Iberian Peninsula

Abstract The influence of multiscale processes such as climate, hydrodynamic and biological alterations on two coastal and estuarine gelatinous zooplankton groups were assessed under a warming decade from 2003 to 2012. At three sampling stations on the Mondego estuary, zooplankton and water samples were collected, evaluating the abundance of chaetognaths and appendicularians. P. friderici and O. dioica were the most prominent species from each gelatinous zooplankton group, occurring in 87% and 86% from all the samples analysed, respectively. Both species displayed higher abundances during summer-autumn months and presented similar seasonal peaks whose densities increased after the first half of the study period. Statistical analysis showed that water temperature, salinity and copepods abundance explained most of the variance in the interannual abundance of both species. This study emphasizes the importance of these less spoken species, which play crucial roles in the ecosystem and points out their resilience to extreme weather events, thriving under future climate change situations.