Estimation of latitudinal shift of Calanus from 1959 to 2004 using generalized additive models

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This study aims to verify the poleward shift of zooplankton species (Calanus finmarchicus, C. glacialis, C. helgolandicus, C. hyperboreus) in the North Atlantic Ocean, and to assess how much of this shift may be due to sea warming, using Generalized Additive Models. To this end, the population gravity centre of observed data from the Continuous Plankton Recorder survey was compared with that predicted from simulation experiments: 1) a model using only climate factors (i.e. niche-based model) to simulate species habitat suitability, 2) a model using temporal and spatial terms to reconstruct the population distribution, and 3) a model using both factors combined, cross-validated. Our findings show that only C. finmarchicus had a consistent poleward shift estimated as 8.1 km per decade in North Atlantic (16.5 km per decade for the Northeast Atlantic) associated with sea warming. This value is lower than that reported by previous studies for zooplankton assemblages in the Northeast Atlantic. C. helgolandicus population has expanded in all directions. C. glacialis and C. hyperboreus, shifted southward, probably responding to cool water penetrating southward in the Labrador Current.