Larval dispersal dynamics of Maja squinado in the Northwestern Mediterranean: a biophysical modeling approach

The Mediterranean spinous spider crab, Maja squinado (Herbst, 1788), is a prized crustacean exploited by Mediterranean coastal fisheries, contributing to local economies and culinary traditions. While stock declines have been reported in some regions, other areas continue to sustain fishing activities, albeit under pressure. Understanding the species' demography is therefore essential for effective future management. To investigate the larval dispersal dynamics of M. squinado in the Mediterranean, a biophysical model was developed, incorporating biological and ecological data such as larval duration and spawning habitats. The tool Ichthyop, designed to study ichthyoplankton dynamics, was employed to perform simulations spanning the period from 2010 to 2020. These simulations were analyzed in the context of global surface water warming trends, yielding maps that illustrated trajectory density, system connectivity, and variations in larval density and dispersal distance over time. The comparative analysis of various scenarios revealed the significant impact of environmental variations on larval connectivity. Specifically, the Tunisia-Sardinia-Corsica complex exhibited strong connectivity, while the Balearic Islands appeared isolated due to the species’ short pelagic larval duration (PLD). The findings highlight the utility of biophysical models in hypothesizing population declines in isolated areas and underscore the necessity of employing diverse modeling approaches at multiple spatial and temporal resolutions. Kernel density estimation (KDE) maps were selected to analyze and visualize the observed simulation scenarios. The results emphasize the importance of considering these changes, particularly the synergies between environmental and biological parameters that influence larval dispersal and connectivity in this species. Such approaches could enhance future conservation and management strategies by accounting for the complex interactions driving population dynamics within the context of a changing Mediterranean ecosystem. • Ichthyop is used to study Maja squinado dispersal and connectivity. • Strong connectivity links Tunisia, Sardinia, and Corsica for this crustacean. • The Balearic Islands are isolated due to a short pelagic larval duration. • Conservation must consider global warming impacts on larval dispersal.