Seasonal variations in the structure and function of zooplankton and micronekton communities: implications for the carbon cycle in the context of climate change

Abstract

Increasing atmospheric CO 2 levels and rising global temperatures have intensified research on the ocean’s role in carbon store. Biological processes play a crucial role in the ocean carbon cycle, transferring carbon from the surface to deeper waters as organic matter through the biological carbon pump. However, the exact contribution of these processes to the carbon export remains poorly understood across much of the ocean. Marine zooplankton, a diverse group of protistan and metazoan consumers, are key components of pelagic food webs, linking primary producers to higher trophic levels and recycling nutrients. Their sensitivity to environmental changes makes them valuable sentinels for long-term monitoring and for understanding climate change impacts on marine ecosystems. Here, we compiled and analyzed five decades (1971–2021) of mesozooplankton biomass data to assess temporal variability in three productive areas of the Canary Current System: North, South and around the islands, and close to the Northwest African coastal upwelling system. Using a Generalized Additive Mixed Model, we examined biomass trends over time, accounting for spatial differences, seasonal cycles, and diel variations. Our analysis revealed a significant long-term decline in mesozooplankton biomass north of the Canary Islands over the 50-year time-series, in contrast to more stable trends in the South and island-associated regions. Additionally, we observed significant differences in biomass between daytime and nighttime periods and across the annual cycle. [...]