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Recent changes in seaweed communities due to rapid shifts of their environment have been largely documented in temperate waters; however, long-term studies are much scarcer. In this study, we investigated the potential of Dinard Herbarium to inform us on temporal changes in seaweed communities of Brittany since the second half of the 19th century. From nearly 3000 specimens collected in France, we identified and, when possible, corrected taxonomic and localisation errors usually encountered in unchecked natural history collections therefore minimising data inaccuracies. This original study aimed to describe the temporal dynamics of this collection and discuss the relevance of Dinard Herbarium in assessing temporal changes in seaweed communities of Brittany. The use of herbaria to assess spatio-temporal changes of seaweed biodiversity is limited, and to our knowledge, this is the first study trying to investigate this potential in the European Atlantic. This work presents new perspectives for inferring temporal changes of seaweed biodiversity. [ABSTRACT FROM AUTHOR]

Aim To assess environmental changes within a marine biogeographical transition zone and how they have affected seaweed assemblages and distributions over the past two decades. Location Brittany (western France, Europe) - a biogeographical transition zone between cold-temperate and warm-temperate regions. Methods We assessed spatio-temporal variation for three environmental parameters [sea-surface temperature ( SST), suspended inorganic matter and chlorophyll a] between 1992 and 2012 in five adjoining regions using generalized linear models. To investigate changes in assemblages and distributional patterns of red seaweeds based on sampling surveys conducted during two separate periods (1992-1998 and 2010-2012), we used two complementary approaches, multivariate data analysis and species distribution models ( SDMs) with a set of modelling procedures. Results Coastal water temperature in Brittany has increased by 0.7 °C on average over the past two decades (0.35 °C per decade). At a finer scale, changes in SST showed that Brittany constitutes a mosaic of contrasting conditions, with the western and north-western regions being colder and less affected by climate change than the other three regions. Our results suggest that increasing SST caused significant changes in subtidal red seaweed assemblages over the 20-year period. Between the two periods, SDMs predicted significant species shifts for seven out of ten representative species, and reductions in the distribution ranges of most species. Main conclusions Our study confirmed important differences across the different regions of the studied biogeographical transition zone. Changes in abiotic parameters and red seaweed assemblages are expected to occur at varying extremes across these regions, with western and north-western Brittany representing the most stable zones that might constitute a potential refuge for certain species when responding to global changes. [ABSTRACT FROM AUTHOR]

We investigated patterns of genetic structure in two sister kelp species to explore how distribution width along the shore, zonation, latitudinal distribution and historical factors contribute to contrasting patterns of genetic diversity. We implemented a hierarchical sampling scheme to compare patterns of genetic diversity and structure in these two kelp species co-distributed along the coasts of Brittany ( France) using a total of 12 microsatellites, nine for Laminaria hyperborea and 11 for Laminaria digitata, of which eight amplified in both species. The genetic diversity and connectivity of L. hyperborea populations were greater than those of L. digitata populations in accordance with the larger cross-shore distribution width along the coast and the greater depth occupied by L. hyperborea populations in contrast to L. digitata populations. In addition, marginal populations showed reduced genetic diversity and connectivity, which erased isolation-by-distance patterns in both species. As L. digitata encounters its southern range limit in southern Brittany ( SBr) while L. hyperborea extends down to mid- Portugal, it was possible to distinguish the effect of habitat continuity from range edge effects. We found that L. digitata did not harbour high regional diversity at its southern edge, as expected in a typical rear edge, suggesting that refuges from the last glacial maximum for L. digitata were probably not located in SBr, but most likely further north. For both species, the highest levels of genetic diversity were found in the Iroise Sea and Morlaix Bay, the two regions in which they are being currently harvested. Preserving genetic diversity of these two foundation species in these areas should, thus, be a priority for the management of this resource in Brittany. [ABSTRACT FROM AUTHOR]