Marine stepping-stones: Connectivity of Mytilus edulis populations between offshore energy installations.

Joop W P Coolen,Richard Crooijmans,Jan Beermann,Leontine E Becking,Silvana N R Birchenough,Hilde Van Pelt,Frank Kleissen,Pieternella C Luttikhuizen,Arjen R Boon,Daan Gerla

doi:10.1111/mec.15364

Abstract

Recent papers have suggested that epifaunal organisms use artificial structures as stepping‐stones to spread to areas that are too distant to reach in a single generation. With thousands of artificial structures present in the North Sea, we test the hypothesis that these structures are connected by water currents and act as an interconnected reef. Population genetic structure of the blue mussel, Mytilus edulis, was expected to follow a pattern predicted by a particle tracking model (PTM). Correlation between population genetic differentiation, based on microsatellite markers, and particle exchange was tested. Specimens of M. edulis were found at each location, although the PTM indicated that locations >85 km offshore were isolated from coastal subpopulations. The fixation coefficient F ST correlated with the number of arrivals in the PTM. However, the number of effective migrants per generation as inferred from coalescent simulations did not show a strong correlation with the arriving particles. Isolation by distance analysis showed no increase in isolation with increasing distance and we did not find clear structure among the populations. The marine stepping‐stone effect is obviously important for the distribution of M. edulis in the North Sea and it may influence ecologically comparable species in a similar way. In the absence of artificial shallow hard substrates, M. edulis would be unlikely to survive in offshore North Sea waters.

Highlights

The past decades have witnessed a steady advance of artificial structures into the marine environment, commonly referred to as “ocean sprawl” (Bishop et al, 2017; Firth et al, 2016)
Results from the species diagnostic locus Me15/16 indicated the presence of nonpure Mytilus edulis genetic material between our samples; a single M. trossulus-type allele was observed as a heterozygote in a Scheveningen sample and a large number of the M. galloprovincialis-type allele were observed as homozygotes and heterozygotes
This study contributes with novel results to the understanding of the marine stepping-stone theory (Adams et al, 2014; Henry et al, 2018)

Summary

Introduction

The past decades have witnessed a steady advance of artificial structures into the marine environment, commonly referred to as “ocean sprawl” (Bishop et al, 2017; Firth et al, 2016). These artificial hard substrates include nearshore elements such as jetties, dikes and beach groins, as well as offshore structures such as oil and gas platforms, wind turbines and buoys. Artificial hard substrates can act as stepping-stones; that is, patches of natural habitat that are normally unconnected may be connected through migration in two or more generations (Fowler et al, 2019). The stepping-stone effect might contribute to a faster distribution of nonindigenous species (Adams et al, 2014; IPIECA, 2010; Macreadie, Fowler, & Booth, 2011)

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