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We examined the phylogeography of the cold-temperate macroalgal species Fucus distichus L., a key foundation species in rocky intertidal shores and the only Fucus species to occur naturally in both the North Pacific and the North Atlantic. North Pacific and North Atlantic oceans (42° to 77° N). We genotyped individuals from 23 populations for a mitochondrial DNA (mtDNA) intergenic spacer (IGS) ( n = 608) and the cytochrome c oxidase subunit I (COI) region ( n = 276), as well as for six nuclear microsatellite loci ( n = 592). Phylogeographic structure and connectivity were assessed using population genetic and phylogenetic network analyses. IGS mtDNA haplotype diversity was highest in the North Pacific, and divergence between Pacific haplotypes was much older than that of the single cluster of Atlantic haplotypes. Two ancestral Pacific IGS/COI clusters led to a widespread Atlantic cluster. High mtDNA and microsatellite diversities were observed in Prince William Sound, Alaska, 11 years after severe disturbance by the 1989 Exxon Valdez oil spill. At least two colonizations occurred from the older North Pacific populations to the North Atlantic between the opening of the Bering Strait and the onset of the Last Glacial Maximum. One colonization event was from the Japanese Archipelago/eastern Aleutians, and a second was from the Alaskan mainland around the Gulf of Alaska. Japanese populations probably arose from a single recolonization event from the eastern Aleutian Islands before the North Pacific-North Atlantic colonization. In the North Atlantic, the Last Glacial Maximum forced the species into at least two known glacial refugia: the Nova Scotia/Newfoundland (Canada) region and Andøya (northern Norway). The presence of two private haplotypes in the central Atlantic suggests the possibility of colonization from other refugia that are now too warm to support F. distichus. With the continuing decline in Arctic ice cover as a result of global climate change, renewed contact between North Pacific and North Atlantic populations of Fucus species is expected. [ABSTRACT FROM AUTHOR]

Aim Ascophyllum nodosum (L.) Le Jolis is a dominant fucoid seaweed occurring along sheltered, rocky shores throughout the North Atlantic (but not in the Pacific), where it is a foundational species of the intertidal community. Its large size and vulnerability to ice-scour have led to the hypothesis that contemporary populations in the north-west Atlantic may be the result of de novo recolonization from the north-east Atlantic since the Last Glacial Maximum (LGM) ( c. 20 ka). We tested this hypothesis. Location Temperate North Atlantic rocky intertidal between c. 42 and 65° N latitude. Methods More than 1300 individuals from 28 populations were sampled from across the entire range of A. nodosum and genotyped for six microsatellite loci, and > 500 individuals were genotyped for two mitochondrial loci, an intergenic spacer (IGS) and the tRNA (W) gene ( trnW). Population structure and historical demography were analysed in a standard population genetics and coalescence framework. Results Based on the presence of private alleles and haplotypes, we found that A. nodosum has survived on both sides of the Atlantic (since before the LGM, dating back to at least the penultimate Eemian interglacial) with similar effective population sizes and divergence times (1.2 and 0.8 Ma). Dispersal has been predominantly from Europe to North America, and there is very weak present-day population differentiation across the North Atlantic. Diversity measures provided additional support for determining the location of refugia. Main conclusions Ascophyllum nodosum was apparently little affected by the LGM, although contemporary climate change is likely to have major effects on its latitudinal distribution on both sides of the North Atlantic. It is a very long-lived species, analogous in virtually all demographic aspects to a tree – resistant to extinction but vulnerable to catastrophic events. The Brittany peninsula is a hotspot of genetic diversity worthy of conservation. [ABSTRACT FROM AUTHOR]

Abstract: Prior to the 1950s, thornback ray (Raja clavata L.) was common and widely distributed in the seas of Northwest Europe. Since then, it has decreased in abundance and geographic range due to over-fishing. The sustainability of ray populations is of concern to fisheries management because their slow growth rate, late maturity and low fecundity make them susceptible to exploitation as victims of by-catch. We investigated the population genetic structure of thornback rays from 14 locations in the southern North Sea, English Channel and Irish Sea. Adults comprised <4% of the total sampling despite heavy sampling effort over 47 hauls; thus our results apply mainly to sexually immature individuals. Using five microsatellite loci, weak but significant population differentiation was detected with a global F ST = 0.013 (P < 0.001). Pairwise F st was significant for 75 out of 171 comparisons. Although earlier tagging studies suggest restricted foraging distances from home areas, the absence of genetic differentiation between some distant populations suggests that a substantial fraction of individuals migrate over wide areas. Autumn/winter locations appear to have a lower level of differentiation than spring/summer, which could be due to seasonal migration. Management and conservation of thornback ray populations will be challenging as population structure appears to be dynamic in space and time. [Copyright &y& Elsevier]