Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle-tracking model coupled to a 3D-hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish The results suggest that 33% of the year-to-year recruitment variability is explained at a regional scale and that a 9-year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (À9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (À58%) and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention À4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.climate change, common sole, connectivity, eastern English Channel, individual-based model, larval dispersal, North Sea, prospective scenarios, recruitment, Solea solea, transport model --

Connectivity and dispersal are important factors for ecosystem dynamics, conservation, and resource management. Dispersal and recruitment success are determined in early life for many marine species. For those larvae that are pelagic, transport from spawning to nursery grounds is driven by hydrodynamic processes. Other environmental factors such as temperature and biological factors such as ecophysiology, behavior, and reproductive strategy (spawning period and spawning grounds) influence the final dispersal pattern and larval survival. We utilized a Lagrangian particle tracking model coupled with a three-dimensional hydrodynamic model (Larvae&Co) to assess the connectivity patterns between spawning and nursery grounds of six commercially exploited flatfish species in the North Sea over a 10-yr period (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006). Standardized analyses have highlighted how spawning and nursery grounds are connected under the combined pressure of environment and life-history traits. Results showed that the six flatfishes can be divided in two groups, each with their specific connectivity patterns. Turbot, common sole, and brill live in two subpopulations in the North Sea; common dab, European flounder, and European plaice represent a single mixed population. In general, the modeled and genetic patterns match, hence showing the strong impact of larval connectivity. The large overlap in connectivity for species that spawn during the same period and the seasonal change in hydrodynamics highlight the strong impact of a summer front in larval dispersal. Our results prove that individual-based modeling is a powerful tool to guide resource management, even in cases of limited biological information.

Understanding the influence of man-made infrastructures on fish population dynamics is an important issue for fisheries management. This is particularly the case because of the steady proliferation of offshore wind farms (OWFs). Several flatfish species are likely to be affected because areas with OWFs in place or planned for show a spatial overlap with their spawning grounds. This study focuses on six commercially important flatfish species in the North Sea: common sole (Solea solea), European plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), brill (Scophtalmus rhombus), European flounder (Platichthys flesus), and common dab (Limanda limanda). We used a particle-tracking model (Larvae&Co) coupled to a 3D hydrodynamic model to assess the effects of spatial overlap of OWFs with the species’ spawning grounds on the larval fluxes to known nursery grounds. An important overlap between planned areas of OWFs and flatfish spawning grounds was detected, with a resulting proportion of settlers originating from those areas varying from 2% to 16%. Our study suggests that European plaice, common dab, and brill could be the most affected flatfish species, yet with some important local disparities across the North Sea. Consequently, the study represents a first step to quantify the potential impact of OWFs on flatfish settlement, and hence on their population dynamics.