A multidisciplinary approach to physical-biological interactions in early life history of marine populations

Traditionally, the quantitative analysis of ecological processes considered separately the temporal population dynamics, under the assumption of homogenous mixing over space, and the spatial distributions of individuals, as a “snapshot” of the species displacement. However, when dealing with populations distributed along a heterogeneous space with fluxes of individuals among separated groups, it is necessary to couple both the spatial and temporal dimensions. A new paradigm for Movement Ecology has been recently proposed renewing the challenge to investigate the driving forces and the ultimate result of movement integrating biological information about interacting species with the mathematical modelling of the organism’s movement. Many models are devoted to the Movement Ecology approach, but the study of species’ early life history in marine ecology has found in the individual-based coupled physical-biological models the specific tool to investigate the dispersal and movement of juveniles. In this thesis some new individual-based coupled physical-biological models for larval dispersal are proposed and analysed. These models are built reproducing the most important biological features of the species considering also the interactions with the external environment. In particular, this work tries to integrate experimental observations and laboratory data to build reliable models through validation and tuning, a not much common practice in this field of modelling. The first part of the thesis presents two dispersal models coupled with a genetic analysis for two species (the European green crab and the white sea bream) in the Adriatic Sea. These models are used with an explanatory approach generating patterns of larval distribution. Larval retention, spill-over and level of connectivity among different places are evaluated. The model results are compared with the results of the genetic analysis. The consistency between the two approaches points out the role of the ocean currents and temperatures in determining the separation or the homogeneity among the analysed groups. The second part of the thesis is devoted to the study of the larval migration of the European eel in the North Atlantic Ocean. An individual- based coupled physical-biological model is developed using alternative scenarios to quantitatively compare the outputs with observed field data. This inferential approach allows to characterise the species biological features, namely body growth, mortality and active locomotion, and to investigate, with the most likely scenario, the inter-annual variation (1960- 2000) of juveniles arriving on the European shelf. This application is used to generate hypothesis that could explain the recruitment collapse observed during the 1980s.