Drivers of interannual abundance changes in gelatinous carnivore zooplankton in the Iberian Peninsula, (Portugal)

• ¹ Center for Marine and Environmental Sciences (MARE), Portugal
• ² Center for Functional Ecology, University of Coimbra, Portugal
• ³ Portuguese Institute of Ocean and Atmosphere (IPMA), Portugal
• ⁴ SeaTox Lab, Faculty of Sciences and Technology, New University of Lisbon, Portugal
• ⁵ UMR9190 Centre pour la biodiversité marine, l'exploitation et la conservation (MARBEC), France

The persistent massive blooms of gelatinous zooplankton recorded during recent decades may be indicative of marine ecosystem changes. In this study, we investigated the potential influence of the North Atlantic climate (NAO) variability on decadal abundance changes of gelatinous carnivore zooplankton in the Mondego estuary, Portugal, over the period 2003-2013. During study period, the community of gelatinous carnivores comprise a larger diversity of hydromedusae than siphonophores; the former dominated by Obelia spp., Lizzia blondina, Clythia hemisphaerica, Liriope tetraphylla and Solmaris corona, while the latter dominated by Muggiaea atlantica. Gelatinous carnivore zooplankton displayed marked interannual variability and mounting species richness over the period examined. Their pattern of abundance shifted towards larger abundances ca. 2007 and significant phenological changes. The latter included a shift in the mean annual pattern (from unimodal to bimodal peak, prior and after 2007 respectively) and an earlier timing of the first annual peak concurrent with enhanced temperatures. These changes were concurrent with the climate-driven environmental variability mainly controlled by the NAO, which displayed larger variance after 2007 along with an enhanced upwelling activity. Structural equation modelling allowed depicting cascading effects derived from the NAO influence on regional climate and upwelling variability further shaping water temperature. Such cascading effect percolated the structure and dynamics of the community of gelatinous carnivore zooplankton in the estuarine system (Fig. 1).