Fine-scale seascape genomics of an exploited marine species, the common cockle Cerastoderma edule, using a multi-modelling approach

Population dynamics of marine species that are sessile as adults are
driven by oceanographic dispersal of larvae from spawning to nursery
grounds. This is mediated by life-history traits such as the timing and
frequency of spawning, larval behaviour and duration, and settlement
success. Here, we use 1725 single nucleotide polymorphisms (SNPs) to study
the fine scale spatial genetic structure in the commercially important
cockle species Cerastoderma edule and compare it to environmental
variables and current-mediated larval dispersal within a modelling
framework. Hydrodynamic modelling employing the NEMO Atlantic Margin Model
(AMM15) was used to simulate larval transport and estimate connectivity
between populations during spawning months (April - September), factoring
in larval duration and inter-annual variability of ocean currents. Results
at neutral loci reveal the existence of three separate genetic clusters
(mean FST=0.021) within a relatively fine spatial scale in the northwest
Atlantic. Environmental Association analysis indicates that oceanographic
currents and geographical proximity explain over 20% of the variance
observed at neutral loci, while genetic variance (71%) at outlier loci was
explained by sea surface temperatures extremes. These results fill an
important knowledge gap in the management of a commercially important and
overexploited species, bringing us closer to understanding the role of
larval dispersal in connecting populations at a fine geographical scale.