Jellyfish biodiversity and abundance patterns in northern Patagonia (Valdés Biosphere Reserve, UNESCO 2014)

Understanding how key components of plankton food webs, such as jellyfish communities, are structured by local hydrography has important management implications for fisheries and higher trophic predators within the ecosystem. Here, we report for the first time on the jellyfish abundance, richness, and diversity distribution across the Nuevo Gulf (42° 42′S, 64° 30′W), a World Heritage Site in Argentine Patagonia and part of the Valdés Biosphere Reserve, during spring (2019 and 2020) and summer (2020 and 2021) at two depths. We found that the most abundant species was the hydromedusae Eucheilota ventricularis, followed by other Leptothecata species, representing more than 50% of the total community's abundance. Abundance and diversity were significantly higher in spring than in summer, with seasonality playing a crucial role in modulating the jellyfish community dynamics and also being related to environmental variables and other mesozooplankton groups. Variability in the abundances across the Gulf and between depths was significantly and positively associated with chlorophyll a and ammonium, but negatively correlated with temperature, agreeing with previous results for the region. Jellyfish were more abundant near the mouth of the Gulf and during spring, possibly due to the connection and exchange of colder and nutrient-enriched water masses with those coming from the continental shelf. Significant correlations were found between jellyfish species and other mesozooplankton groups in spring. Our results highlight the importance of intensifying sampling in the vertical and horizontal dimensions along an annual cycle to begin to elucidate and increase the current scarce knowledge about the jellyfish's distribution and abundance patterns in northern Patagonian gulfs. •Jellyfish abundance and diversity from Nuevo Gulf (Argentina) obtained for the first time.•Abundance was higher during spring, associated to chlorophyll a and ammonium, but negatively related to temperature.•Seasonality is an important factor in modulating the jellyfish community dynamic.