S. Bennett and T. Wernberg, Canopy facilitates seaweed recruitment on 540 subtidal temperate reefs, Journal of Ecology, vol.102, pp.1462-1470, 2014.

D. Borcard, F. Gillet, and P. Legendre, Numerical ecology with R. Springer, vol.542, 2011.

, Science & Business Media

E. Boudière, C. Maisondieu, F. Ardhuin, M. Accensi, and L. Pineau-guillou, , vol.544

J. Lepesqueur, A suitable metocean hindcast database for the design 545 of Marine energy converters, International Journal of Marine Energy, pp.40-546, 2013.

F. Gohin, Annual cycles of chlorophyll-a, non-algal suspended particulate 602 matter, and turbidity observed from space and in-situ in coastal waters, Science, vol.603, pp.705-732, 2011.

M. H. Graham, Effects of local deforestation on the diversity and structure of 605 southern California giant kelp forest food webs, Ecosystems, vol.7, pp.341-357, 2004.

J. P. Grime, Competitive exclusion in herbaceous vegetation, Nature, vol.242, pp.607-344, 1973.

S. Hawkins and E. Harkin, Preliminary canopy removal experiments in algal 609 dominated communities low on the shore and in the shallow subtidal on the 610 Isle of Man, Botanica Marina, vol.28, pp.223-230, 1985.

S. P. Hubbell, The unified neutral theory of biodiversity and biogeography, 2001.

G. E. Hutchinson, Concluding remarks. Cold Spring Harbor Symposia on 614, 1957.

, Quantitative Biology, pp.415-427

L. M. Irvine, Seaweeds of the British Isles, vol.1, p.616, 1983.

. Cryptonemiales, Palmariales, Rhodymeniales. British Museum 617 (Natural History)

L. M. Irvine, Y. M. Chamberlain, and C. A. Maggs, Seaweeds of the British Isles, p.619, 1994.

, Rhodophyta, pt. 2B., Corallinales, Hildenbrandiales. The Natural History 620 Museum, vol.1

J. M. Kain, A view of the genus Laminaria. Oceanography and marine biology: 622 an annual review, vol.17, pp.101-161, 1979.

S. A. Keith, A. P. Kerswell, and S. R. Connolly, Global diversity of marine 624 macroalgae: environmental conditions explain less variation in the tropics, 2014.

, Global Ecology and Biogeography, vol.23, pp.517-529

R. P. Kelly and S. R. Palumbi, Genetic structure among 50 species of the 627 northeastern Pacific rocky intertidal community, PLoS ONE, vol.5, p.8594, 2010.

A. P. Kerswell, Global biodiversity patterns of benthic marine algae, Ecology, vol.629, pp.2479-2488, 2006.

R. Kindt and R. Coe, Tree diversity analysis: a manual and software for 631 common statistical methods for ecological and biodiversity studies, World, vol.632, 2005.

A. Centre,

B. P. Kinlan and S. D. Gaines, Propagule dispersal in marine and terrestrial 634 environments: a community perspective, Ecology, vol.84, 2003.

M. Kuhn, J. Contributions, S. W. Wing, and A. Williams, , p.636

T. Engelhardt, Z. Cooper, and . Mayer, Brenton Kenkel, the R Core Team, p.637

M. Benesty, R. Lescarbeau, A. Ziem, and L. Scrucca, Yuan 638 Tang and Can Candan. (2015) caret: Classification and Regression Training

J. Le-fèvre, Aspects of the biology of frontal systems, Advances in Marine, vol.640, pp.163-299, 1987.

J. Leclerc, P. Riera, M. Laurans, C. Leroux, L. Lévêque et al., , p.642, 2015.

, Community, trophic structure and functioning in two contrasting Laminaria 643 hyperborea forests, Estuarine, Coastal and Shelf Science, vol.152, pp.11-22

M. A. Leibold, M. Holyoak, N. Mouquet, P. Amarasekare, J. M. Chase et al., , p.645

M. F. Holt, R. D. Shurin, J. B. Law, R. Tilman, D. Loreau et al., The metacommunity concept: a framework for multi-scale community 647 ecology, Ecology Letters, vol.646, pp.601-613, 2004.

M. A. Leibold and M. A. Mcpeek, Coexistence of the niche and neutral 649 perspectives in community ecology, Ecology, vol.87, pp.1399-1410, 2006.

F. Leliaert, R. J. Anderson, J. J. Bolton, and E. Coppejans, Subtidal understorey 651 algal community structure in kelp beds around the Cape Peninsula, p.652, 2000.

S. Cape and . Africa, Botanica Marina, vol.43, pp.359-366

J. B. Logue, N. Mouquet, H. Peter, and H. Hillebrand, Empirical approaches to 654 metacommunities: a review and comparison with theory, Trends in Ecology & 655 Evolution, vol.26, pp.482-491, 2011.

C. A. Maggs and M. H. Hommersand, Seaweeds of the British Isles, vol.1, p.657, 1993.

P. 3. Rhodophyta and . Ceramiales, The Natural History Museum

K. H. Mann, Seaweeds: their productivity and strategy for growth Science, vol.182, pp.659-975, 1973.

E. J. Mcintire and A. Fajardo, Beyond description: the active and effective way 661 to infer processes from spatial patterns, Ecology, vol.90, pp.46-56, 2009.

R. J. Miller and R. J. Etter, Shading facilitates sessile invertebrate dominance in 663 the rocky subtidal Gulf of Maine, Ecology, vol.89, pp.452-462, 2008.

F. Munoz, Distance-based eigenvector maps (DBEM) to analyse 665 metapopulation structure with irregular sampling, Ecological Modelling, vol.220, pp.666-2683, 2009.

T. A. Norton, Dispersal by macroalgae, British Phycological Journal, vol.27, pp.293-668, 1992.

J. Oksanen, G. F. Blanchet, R. Kindt, P. Legendre, P. R. Minchin et al., , p.670

G. L. Simpson, P. Solymos, M. Henry, H. Stevens, and H. Wagner, vegan: Community Ecology Package, p.671, 2015.

S. Ollier, P. Couteron, and D. Chessel, Orthonormal transform to decompose 673 the variance of a life-history trait across a phylogenetic tree, Biometrics, vol.62, pp.471-477, 2006.

L. V. Oppliger, P. Von-dassow, S. Bouchemousse, M. Robuchon, and M. Valero, , p.676

J. A. Correa, S. Mauger, and C. Destombe, Alteration of sexual 677 reproduction and genetic diversity in the kelp species Laminaria digitata at the 678 southern limit of its range, PLoS ONE, vol.9, 2014.

C. Pehlke and I. Bartsch, Changes in depth distribution and biomass of 680 sublittoral seaweeds at Helgoland (North Sea) between, 1970.

, Climate Research, vol.37, pp.135-147

T. Platt and K. L. Denman, Spectral analysis in ecology, Annual Review of 683 Ecology and Systematics, vol.6, pp.189-210, 1975.

. R-core-team, R: a language and environment for statistical computing. R 685 Foundation for Statistical Computing, 2015.

D. Raffaelli and S. Hawkins, Intertidal Ecology, p.687, 1996.

U. K. London,

C. R. Rao, A review of canonical coordinates and an alternative to 689 correspondence analysis using Hellinger distance, Questiió: Quaderns 690 d'Estadística, Sistemes, Informatica i Investigació Operativa, vol.19, pp.23-63, 1995.

M. Robuchon, L. Le-gall, S. Mauger, and M. Valero, Contrasting genetic 692 diversity patterns in two sister kelp species co-distributed along the coast of 693, 2014.

F. Brittany, Molecular Ecology, vol.23, pp.2669-2685

M. Robuchon, M. Valero, D. Gey, and L. Le-gall, How does molecular-assisted 695 identification affect our estimation of ?, ? and ? biodiversity? An example from 696 understory red seaweeds (Rhodophyta) of Laminaria kelp forests in Brittany, p.697, 2015.

. France and . Genetica, , vol.143, pp.207-223

M. Robuchon, M. Valero, E. Thiébaut, and L. Le-gall, Data from: Multi-scale 699 drivers of community diversity and composition across tidal heights: an 700 example on temperate seaweed communities, Journal of Ecology, 2017.

J. Salomon and M. Breton, An atlas of long-term currents in the Channel, 1993.

, Oceanologica Acta, vol.16, pp.439-448

E. J. Sbrocco and P. H. Barber, MARSPEC: ocean climate layers for marine 705 spatial ecology: Ecological Archives E094-086, Ecology, vol.94, pp.979-979, 2013.

C. E. Shannon, A mathematical theory of communication, Bell System 707 Technical Journal, vol.27, pp.379-423, 1948.

D. A. Smale, M. T. Burrows, P. Moore, N. O'connor, and S. J. Hawkins, Threats 709 and knowledge gaps for ecosystem services provided by kelp forests: a 710 northeast Atlantic perspective, Ecology and Evolution, vol.3, pp.4016-4038, 2013.

D. A. Smale, G. A. Kendrick, and T. Wernberg, Subtidal macroalgal richness, 712 diversity and turnover, at multiple spatial scales, along the southwestern 713 Australian coastline, Estuarine, Coastal and Shelf Science, vol.91, pp.224-231, 2011.

M. D. Spalding, H. E. Fox, G. R. Allen, N. Davidson, Z. A. Ferdaña et al., , p.715

B. S. Halpern, M. A. Jorge, A. L. Lombana, and S. A. Lourie, Marine 716 ecoregions of the world: a bioregionalization of coastal and shelf areas, 2007.

, Bioscience, vol.57, pp.573-583

R. S. Steneck, M. H. Graham, B. J. Bourque, D. Corbett, J. M. Erlandson et al.,

M. J. Tegner, Kelp forest ecosystems: biodiversity, stability, resilience 720 and future, Environmental Conservation, vol.29, pp.436-459, 2002.

D. Tilman, Resource competition and community structure, 1982.

M. Valero, C. Destombe, S. Mauger, C. Ribout, and C. R. Engel,

F. Tellier, Using genetic tools for sustainable management of kelps: a 725 literature review and the example of Laminaria digitata, Cahiers de Biologie, vol.726, 2011.

M. , , vol.52, pp.467-483

M. A. Vanderklift, P. S. Lavery, and K. I. Waddington, Intensity of herbivory on 728 kelp by fish and sea urchins differs between inshore and offshore reefs, 2009.

, Marine Ecology Progress Series, vol.376, pp.203-211

T. Wernberg, S. Bennett, R. C. Babcock, T. De-bettignies, K. Cure et al., , p.731

M. Dufois, F. Fromont, J. Fulton, C. J. Hovey, and R. K. , Climate-driven 732 regime shift of a temperate marine ecosystem, Science, vol.353, pp.169-172, 2016.

T. Wernberg and S. D. Connell, Physical disturbance and subtidal habitat 734 structure on open rocky coasts: effects of wave exposure, extent and intensity, Journal of Sea Research, vol.735, pp.237-248, 2008.

T. Wernberg, G. A. Kendrick, and J. C. Phillips, Regional differences in kelp-737 associated algal assemblages on temperate limestone reefs in south, p.738, 2003.

, Australia. Diversity and Distributions, vol.9, pp.427-441

T. Wernberg, G. A. Kendrick, and B. D. Toohey, Modification of the physical 740 environment by an Ecklonia radiata (Laminariales) canopy and implications for 741 associated foliose algae, Aquatic Ecology, vol.39, pp.419-430, 2005.

. Fig, Map showing the 19 sampling sites distributed in the four sectors along the 768

F. Brittany-coastline, Sites are: Guimereux (1), p.769

. Moulin, Primel (6), Les Amas du Cap (5), vol.770, p.771

S. Mathieu, Houat 772 2 (18) and Houat 1 (19). For site coordinates, see Appendix S1, Pointe du Grand Gouin (17)

, Comparison of species diversity estimates between infralittoral fringe 775 communities and subtidal communities across space. (a) Species richness (SR) by 776 sector, (b) Shannon diversity (H') by sector, (c) SR by site and (d) H' by site. For site 777 names

, Plots of site scores on the first two axes of the principal components analyses 780 of site-by-species abundance matrices (a) for infralittoral fringe communities and (b) 781 for subtidal communities. For each score, a smoothed scalogram (the 18 Moran's 782 eigenvector maps [MEMs] are assembled in 6 groups) indicates the portion of 783 variance

, For each scalogram, the scale corresponding to the highest R 2 (in dark gray) is 785 tested using 999 permutations of the observed values (P values are given). The 95% 786 confidence limit is also represented by the line of plus signs

, Plots of site scores on the first two axes of the redundancy analyses using the 789 site-by-environment matrices as predictors (a) for infralittoral fringe communities and 790 (b) for subtidal communities. For each score, a smoothed scalogram (the 18 Moran's 791 eigenvector maps [MEMs] are assembled in 6 groups) indicates the portion of 792 variance

, For each scalogram, the scale corresponding to the highest R 2 (in dark gray) is