Modelling coastal connectivity in the Mediterranean Sea: Similar effects of changes in hydrodynamics and reduction in planktonic duration

Climate change can affect the dispersal of marine organisms and the
connectivity of their populations through changes in hydrodynamics and the
reduction of the planktonic duration of propagules. Few studies have
investigated these effects over regional to global scales across a variety
of release dates and sites. Here, we use hydrodynamic Lagrangian modelling
to investigate these effects, their seasonal variation, and how they are
modulated by the planktonic duration of dispersing propagules. Marine
coastal organisms with planktonic propagules dispersed passively by ocean
currents (e.g., seagrasses, mussels, sea urchins). Simulations of
propagule dispersal were carried out using particle tracking model
simulations driven by sea current velocity fields derived from the POLCOMS
hydrodynamic model, under the Representative Concentration Pathway 8.5. We
released propagules over three decades and followed their transport for
planktonic durations up to 60 days. We quantified connectivity using three
site-level variables (i.e., dispersal distance, coastal retention, and
netflow) and a clustering approach. Changes in hydrodynamics and reduction
in planktonic duration had similar effects on connectivity, leading to
changes of up to 60% of the values of the 2020s. While the largest effects
of changes in hydrodynamics were confined to a few areas, the effects of
the reduction in planktonic duration were less variable spatially and
seasonally. The effects of hydrodynamic changes were larger and more
variable in species with longer planktonic durations. Because they had
similar magnitudes, both the effects of changes in hydrodynamics and the
reduction in planktonic duration should be considered in future studies.
The expected changes in connectivity have potential consequences for
genetic structure, the effectiveness of protected areas, and biological
invasions. The dispersal dataset produced here is openly accessible and
will support further research in these critical areas.