Numerical modelling of physical processes governing larval transport in the Southern North Sea

Abstract

A three-dimensional hydrodynamic model (GETM) was coupled with a particle tracking routine (GITM) to study the inter-annual variability in transport paths of particles in the North Sea and English Channel. For validation, a comparison with observed drifter trajectories was made. The aim was to investigate to what extent variability in the hydrodynamic conditions alone (reflecting passive particle transport) contributed to inter-annual variability in transport of eggs and larvae. In this idealized study, no a-priori selection of spawning grounds or periods was made and no active behaviour (vertical migration) or mortality were included. Egg and larval development towards coastal nursery areas was based solely on sea water temperature, while settlement areas were defined by a threshold water depth. Results showed strong inter-annual variability in drift direction and distance, caused by a combination of wind speed and direction. Strong inter-annual variability was observed both in absolute amount of settlement in coastal areas, as well as in the relative importance of the different areas. Settlement in the western Dutch Wadden Sea not only showed inter-annual variability, but patterns were also variable within each year and revealed seasonal changes in the origin of particles

Variation that can be expected when using particle tracking models in connectivity studies

“…Comparing modelled drift routes with observations is generally more difficult than comparing the OCM derived fluxes or temperatures as specific field measurement are lacking against which results can be compared. Sub surface Argo floats mainly represent the combined effect of wind and surface currents and also show high variability in observed trajectories (Hill et al, 2008;Tiessen et al, 2014). In model drift studies generally A C C E P T E D M A N U S C R I P T 5 several thousand particles are released while in reality experiments are restricted to much smaller numbers, although the observed diversity of routes taken by the buoys indicates that many more floats would be needed for a representative analysis.…”

“…year-to-year variability (Lacroix et al, 2016), modelled and observed distribution of plaice larvae (Hufnagl et al, 2013) or drift of buoys (Tiessen et al, 2014).…”

“…Single buoys have been released and followed in the field, which can be used as e.g. shown by König and Schrum (1997) or Tiessen et al (2014), but only to a certain extent. Other potential tracers such as larvae, zooplankton and chlorophyll as well as nutrients like nitrogen undergo natural production/degradation processes and are therefore of limited value.…”

Connectivity of larval stages of sedentary marine communities between hard substrates and offshore structures in the North Sea

“…More recently, the impact of pelagic dispersal on connectivity has been studied using particle tracking approaches that model both hydrodynamics and larval behaviour. These models have been used to assess recruitment of commercial fish species 15 – 20 and jellyfish 21 . Corridors between structures such as pipelines provide a mechanism for colonisation of reef species that do not have pelagic dispersal 6 .…”

“…This paper focusses on connectivity through planktonic life stages of several different sedentary species commonly found in association with man-made structures using an existing particle tracking model 20 , 21 . The General Individuals Transport Model (GITM) includes physical particle advection based on current fields from hydrodynamic models, diffusion, biological development, and behaviour 18 , 21 .…”