Dynamic factor analysis of mesozooplankton variability in the Gulf of Cádiz

Abstract

Mesozooplankton plays a key role in pelagic ecosystems, acting as an intermediate trophic link and a modulator of biogeochemical cycles. However, its dynamics remain poorly understood on the northeastern shelf of the Gulf of Cádiz, a highly productive region supporting important coastal fisheries. This study investigates the spatiotemporal variability of mesozooplankton in this region using a six-year dataset of monthly observations from a spatially dense monitoring network. The objective is to assess how oceanographic and trophic forcing controls the spatiotemporal variability of mesozooplankton biovolume along the northeastern shelf of the Gulf of Cádiz. To this aim, Dynamic Factor Analysis (DFA) was applied to the mesozooplankton biovolume time series to extract shared latent temporal signals. The analysis identified four optimal latent temporal signals reflecting distinct components of mesozooplankton variability across the shelf. Seasonality emerged as the dominant mode of variability, although its expression varied spatially in response to local and regional forcings. Mesozooplankton dynamics exhibit a clear latitudinal organization, coherent with the contrasting wind regimes that characterize the northern and southern sectors of the shelf. This regional structure is further modulated by coastal–offshore gradients and by the influence of the Strait of Gibraltar in the Trafalgar area, where enhanced hydrodynamic activity leads to locally distinct responses. Along the coastal band, river influence plays a dual role, enhancing productivity at intermediate distances from the estuary while constraining trophic transfer under persistent estuarine conditions at the Guadalquivir mouth. Overall, these results highlight the complexity of the mechanisms shaping mesozooplankton spatiotemporal dynamics in the Gulf of Cádiz and contribute to a better understanding of the role of this key trophic component in a highly productive ecosystem that remains poorly studied in this region.