Marine functional connectivity (MFC) refers to the flows of organic matter, genes, and energy that are caused by the active and passive movements of marine organisms. Occurring at various temporal and spatial scales, MFC is a dynamic, constantly evolving global ecological process, part of overall ecological connectivity, but with its own distinct and specific patterns. Geological and historical archives of changes in the distributions, life histories, and migration of species can provide baselines for deciphering the long-term trends (decadal to millions of years) and variability of MFC. In this food-for-thought paper, we identify the different types of geohistorical data that can be used to study past MFC. We propose resources that are available for such work. Finally, we offer a roadmap outlining the most appropriate approaches for analysing and interpreting these data, the biases and limitations involved, and what we consider to be the primary themes for future research in this field. Overall, we demonstrate how, despite differences in norms and limitations between disciplines, valuable data on ecological and societal change can be extracted from geological and historical archives, and be used to understand changes of MFC through time.

The meagre Argyrosomus regius, one of the largest sciaenidae in the world, is a valuable resource for fisheries and aquaculture. Despite its socioeconomic relevance, knowledge about population dynamics and wild stocks is still scarce, and conservation risks are associated with overexploitation. Two genetic distinct groups, one in the North Atlantic Ocean and one in the eastern Mediterranean Sea, were identified by previous studies. However, little is known about the genetic structure of the Atlantic group, where four important spawning areas have been identified. To assess if each spawning area is an independent breeding unit, the genetic diversity, populational structure, and demographic history of A. regius along the North–East and Eastern Central Atlantic coast were analyzed, using 15 microsatellite loci. Results corroborate the hypothesis tested, suggesting four genetic groups: a first group encompassing individuals from the Gironde spawning area, a second group encompassing individuals from the Tagus spawning area, a third group corresponding to individuals captured in the Algarve region, and a forth group gathering individuals from Morocco and Mauritania. This study reveals the need for specific fisheries management plans considering genetic structure information, and highlights the need for international cooperation.

Plasticity in fish movement patterns is frequently observed in euryhaline species. Otolith shape and chemical composition are natural recorders of the environmental conditions experienced by individual fish, providing valuable tools to reconstruct habitat use and movement patterns. The European sea bass (Dicentrarchus labrax) is a euryhaline species for which partial migration has been suggested, whereby some individuals remain resident while others migrate in coastal and marine environments, but the use of freshwater habitats by adults has only been reported recently. To assess the existence of distinct contingents, this study analysed the otolith shape and chemical composition of sea bass collected in freshwater, adjacent coastal areas and distant coastal areas using Wavelet reconstructions and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Both approaches identified a divergent life-history strategy within the sea bass population, characterized by a consistent use of freshwater habitat. Otolith chemistry further suggested that life histories differentiate with age, becoming especially evident from age two onward, when freshwater-associated signatures start to become more noticeable. These findings reveal the ecological plasticity of European sea bass and highlight the importance of sea-land connectivity for the conservation of euryhaline species.