Seasonal dynamics of zooplankton communities in a recent lava delta on an oceanic island in the Central East Atlantic Ocean

Abstract We examined the structure of the zooplankton community in a Special Area of Conservation affected by the recent formation of lava deltas caused by a volcanic eruption on the island of La Palma (Canary Islands) in the Central East Atlantic Ocean. Seasonal variability in biomass, abundance, and composition of the zooplankton community was analyzed, both in total and within different size ranges. The results showed higher biomass values in winter at 30 m and in spring–summer at 10 m depth, possibly related to seasonal changes in food availability and seawater temperature. Significant differences were observed in the biomass of the smaller size range compared to larger sizes. Similarly, organisms in the smaller size range were the most abundant, primarily due to the community being dominated by copepods, which represented 80.43% of the total abundance in winter, decreasing to 47.14% in spring–summer. At the same time, a significant increase was observed in decapod larvae, gastropods, invertebrate eggs, and cladocerans during the warmer season. An increase in gelatinous organisms, especially siphonophores, was also observed in spring–summer for the largest size range, suggesting potential seasonal changes in the zooplankton trophic structure. This study indicates a limited direct impact of volcanic activity on zooplankton biomass but highlights the importance of understanding seasonal variability in community structure for managing marine conservation. Continuous monitoring of zooplankton dynamics is crucial for detecting potential future impacts on the food web and developing targeted conservation management strategies.