Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Abstract

Populations along the northern boundary of a marine species' distributional range in the NE Atlantic are expected to harbor lower standing genetic variation as a consequence of postglacial expansion following the last glacial maximum. Founder events and marginal habitat availability may render the edge populations more vulnerable to anthropogenic stress and less capable of rapid adaptation to global climate change, a concern for conservation and management. We analyzed meadow architecture, persistence and connectivity within and among 15 locations (600 samples genotyped with 8 microsatellite loci) in 3 fjords in Troms County, Norway (69°N). Whereas global mean allelic diversity (standardized for sample size) was in accordance with previous studies using the same markers, more extensive sampling revealed a broader range of allelic richness (mean = 2.85; range = 1.84 to 4.21) in the regional pool. Genotypic diversity was typically high, whereas large genets were rare (2 out of 15 locations). Population differentiation (F ST ) was 2 to 6 times higher between fjords than within fjords. A Bayesian (STRUCTURE) analysis also strongly supported the genetic distinctness of each fjord. Although 9 locations within the 60 km long Balsfjord were connected by gene flow, demographic connectivity may actually be low, as fixed differences were observed at 6 of the 9 locations, along with significantly positive inbreeding coefficients and strong substructure. Overall, our results suggest that these northern, leading-edge meadows are healthy, but vigilance is required to avoid further losses. Fjord-level management, especially of the larger fjords, will be sufficient to capture the range of variation.

The genome of the seagrass Zostera marina reveals angiosperm adaptation to the sea

“…Tissues were immediately frozen in LN 2 and stored at −80 °C for later DNA and RNA extraction. Monoclonality was verified by genotyping 40 ramets of the mega-clone with six highly polymorphic, microsatellite loci 30 . There was no evidence for polyploidy 25,31,32 (Z. marina is 2n = 12) or somatic mutations 33 as assessed by multiple peaks in the microsatellite chromatograms.…”

Eelgrass Zostera marina in subarctic Greenland: dense meadows with slow biomass turnover in cold waters

“…The current warming of the globe is occurring twice as fast in the Arctic as for the globe on average (IPCC 2007), rendering the Arctic particularly susceptible to the effects of climate change. While several studies have documented the negative effects of high temper a tures on seagrass growth and survival at lower latitudes (Thayer et al 1984, Santamaría-Gallegos et al 2000, Nejrup & Pedersen 2008, Bergmann et al 2010, knowledge on productivity, growth and reproduction of eelgrass and probable responses to warming are lacking in the typically colder climates at the northern distribution limit (McRoy 1974, Duarte et al 2002, Berger 2011, Jørgensen & Bkkby 2013, Olsen et al 2013.…”

Phylogeography of the temperate marine bivalveCerastoderma edule(Linnaeus, 1758) (Bivalvia: Cardiidae) in the Subarctic: Unique diversity and strong population structuring at different spatial scales

“…The Lofoten circulation which formed in early Holocene as a part of the North Atlantic Drift presumably could be involved in filtering of genotypes penetrated the north during postglacial recolonization of the Scandinavian Peninsula coastline. Similarly to C. edule , the eelgrass Zostera marina shows high genetic diversity in Northern Norway, in combination with low demographic connectivity between the populations from adjacent fjords (Olsen et al., ). Z. marina meadows in these fjords are located on the northeastern edge of the uninterrupted part of eelgrass distribution range in Europe, eelgrass has very scattered distribution in the Barents Sea and again become abundant in the White Sea (Green & Short, ).…”

“…At the same time, shores of the Norwegian and Barents Seas constitute about one quarter of the length of the geographical range of temperate intertidal communities in Europe. Recent studies of brown algae and seagrasses (Coyer, Hoarau, Van Schaik, Luijckx, & Olsen, ; Coyer, Hoarau, Costa et al., ; Olsen et al., ) show that subarctic populations can be genetically diverse and isolated from other parts of their distribution ranges.…”