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Marine Ecology: Temperate Systems

Connectivity and gene flow in temperate Alcyonacea (Octocorals): Implications for Marine Protected Area (MPA) designation

Connectivity between marine populations via larval dispersal is a key factor in determining genetic diversity. A high level of genetic diversity is typically regarded as being crucial for ecosystem function and resilience, and for recovery from anthropogenic and climatic disturbance. Connectivity is therefore a key consideration in the design of marine reserve networks, as reserves must be appropriately sized and spaced to facilitate propagule dispersal between source and sink populations of taxa of conservation interest. However, the extent of connectivity between and within most marine ecosystems is poorly understood and larval dispersal is frequently inferred (rather than being measured direclty); moreover, such data are rarely available for temperate or invertebrate taxa, many of which are threatened by human activity (e.g. destructive fishing practices) and climate change. In addition, some evidence suggests that colder temperatures characteristic of higher latitudes may prolong pelagic larval duration and, therefore, connectivity may depend upon temporal and spatial variation in life history traits in addition to physical processes, suggesting that existing guidelines established to design MPAs in tropical areas may be inapplicable in temperate regions.

To address this shortfall, this study assessed connectivity and gene flow of two octocorals: Eunicella verrucosa (pink sea fan) and Alcyonium digitatum (dead man's fingers) using molecular markers (microsatellites) over a range of geographical scales. These data are vital to validate the effectiveness of the boundaries of the current UK MPA network, as proposed in the UK Marine and Coastal Access Bill (2012), and will identify other areas in European waters where these octocorals may by exhibt reduced genetic diversity. We determined the extent to which variation in dispersal potential of the two species affected connectivity, and assessed the extent of inbreeding across the range of each species. Eunicella verrucosa is red listed by the IUCN and has a ‘vulnerable’ status; in some areas, UK populations have been decimated by trawling and scallop-dredging, and are also subject to disease. Baseline data concerning levels of connectivity between populations of both species are currently non-existent and are fundamental to the development of conservation strategies for these and other species with similar life history traits and ranges.

We have analysed a wide-ranging collection of octocoral specimens from England, Wales, Ireland, France, Spain and Portugal, enabling us to assess connectivity between populations around the British Isles and those elsewhere in the seas of western Europe. This work was funded by Natural England (project no. RP0286), the NERC GW4+ initiative and the European Union Assemble Programme (agreement no. 227799).

A short video providing an overview of the project is available here.

A blog presented by the journal PeerJ on predicted range expansions in octocorals is available here.

Molecular markers useful in assessing genetic connectivity within populations of these octocorals are published in the journal Conservation Genetics Resources, and studies of genetic connectivity in these species are available in the journal Heredity, Marine Policy and PeerJ (see below).

  • Holland, L.P., Dawson, D.A., Horsburgh, G.J. and Stevens, J.R. (2013) Isolation and characterization of eleven microsatellite loci from the ubiquitous temperate octocoral Alcyonium digitatum (Linnaeus, 1758). Conservation Genetics Resources 5: 767–770.
  • Holland, L.P., Dawson, D.A., Horsburgh, G.J., Krupa, A.P. and Stevens, J.R. (2013) Isolation and characterization of fourteen microsatellite loci from the endangered octocoral Eunicella verrucosa (Pallas, 1766). Conservation Genetics Resources 5: 825–829. 
  • Holland, L.P. and Stevens J.R. (2014) Assessing the genetic connectivity of two octocoral species in the Northeast Atlantic (NECR152). Natural England, ISBN 978-1-78354-111-9    
  • Holland, L.P., Jenkins, T.L. and Stevens, J.R. (2017) Contrasting patterns of population structure and gene flow facilitate exploration of connectivity in two widely distributed temperate octocorals. Heredity (online 15/3/2017), DOI 10.1038/hdy.2017.14.
  • Jenkins, T.L. and Stevens, J.R. (2018) Assessing connectivity between MPAs: Selecting taxa and translating genetic data to inform policy. Marine Policy, 94: 165–173
Other recent papers from the group exploring genetic diversity, gene flow and connectivity in temperate marine invertebrates include the following:
  • Jenkins, T.L. and Stevens, J.R. (2022). Predicting habitat suitability and range shifts under projected climate change for two octocorals in the north-east Atlantic. PeerJ, 10: e13509.
  • Jenkins, T.L., Guillemin, ML, SimonNutbrown, C, Burdett, HL, Stevens, J.R. and Peña, V (2021). Whole genome genotyping reveals discrete genetic diversity in northeast Atlantic maerl beds.  Evolutionary Applications, 14: 1558–1571.
  • Ellis, C.D., Jenkins, T.L., Svanberg, L., Eriksson, S.P. and Stevens J.R. (2020) Crossing the pond: genetic assignment detects lobster hybridisation. Scientific Reports, 10: 7781.
  • Jenkins, T.L., Ellis, C. and Stevens, J.R. (2019) SNP discovery in European lobster (Homarus gammarus) using RAD sequencing.  Conservation Genetics Resources, 11: 253–257. 
  • Jenkins, T.L., Ellis, C., Triantafyllidis, A. and Stevens, J.R. (2019) Single nucleotide polymorphisms reveal a genetic cline across the north-east Atlantic and enable powerful population assignment in the European lobster.  Evolutionary Applications, accepted 11/7/2019. 
  • Jenkins, T.L., Castilho, R. and Stevens, J.R. (2018) Meta-analysis of northeast Atlantic marine taxa shows contrasting phylogeographic patterns following post-LGM expansions. PeerJ, 6: e5684.

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