Aim Foundation species sustain biodiversity by providing habitat, resources, and protection from environmental stress. However, their influence on environmental severity and variability and their role in shaping diversity across spatial scales remain poorly understood. We conducted a large-scale study to assess how environmental conditions and community diversity vary between areas with and without canopy-forming macroalgae across local to regional spatial scales.Location Latitudinal range from 28 degrees 34 ' N to 54 degrees 11 ' N, encompassing both the Northeast Atlantic and Western Mediterranean regions.Time Period 2019-2020.Major Taxa Studied Marine macroalgae and benthic invertebrates.Methods Using a standardised nested sampling design across 13 sites in two marine regions (the Northeast Atlantic and Western Mediterranean) we compared the intensity and variability of temperature and light intensity, as well as community alpha- and beta-diversity, between intertidal rocky areas with and without canopy-forming macroalgae. Data were analysed by means of linear mixed-effects models.Results There were regional differences in variations of environmental conditions between habitats: NE Atlantic macroalgal canopies were characterised by lower environmental extremes and variability-especially in summer-than open rock areas, whereas differences between habitats were small in the W Mediterranean. Likewise, differences in alpha- and beta-diversity between habitats were region-specific and scale-dependent: in the NE Atlantic, alpha-diversity was higher in the presence of canopies than in open rock areas from local to regional scales, while beta-diversity decreased in canopy stands with increasing spatial scale. In the W Mediterranean, alpha-diversity was higher under canopies than on open rock at the regional scale, whereas beta-diversity was higher under canopies at small to intermediate scales.Main Conclusions Our results support the view that key environmental conditions and biodiversity on intertidal rocky shores differ between areas characterised by the presence or absence of canopy-forming macroalgae acting as foundation species, across a hierarchy of spatial scales.

Global warming is driving contraction of species’ ranges through migration and mortality at their warm edge. However, for most species more subtle, sub-lethal changes in performance will be a more ubiquitous response to the Anthropocene. It has been suggested that reduction in body size will be a universal response to warming for cold-water species. Here we tested this hypothesis for two dominant kelp species in the northern and southern hemispheres, respectively. We tested if populations from cool and warm environments would be morphologically distinct, with warm-water populations displaying structural features indicative of sub-optimal conditions (smaller sizes). We found empirical evidence consistent with size reduction of kelp stipes, blades, and biomass of associated epiphytes from cool to warm water in both hemispheres. These changes are ecologically significant because they affect how kelps engineer their local environment, the three-dimensional habitat they create, and the associated communities they support. Reduced size of cold-water habitat forming species such as kelps may be a sublethal effect of warming that could have widespread but previously overlooked effects on the structure of ecosystems and the services that they provide.

Climate change is predicted to increase the prevalence of marine heatwaves with an increase in heatwave frequency and intensity. While some studies have shown the effect of marine heatwaves in warm temperate climates and the effect of overall higher temperature in warm and cold temperate climates, it is yet not entirely understood how heatwaves impact marine urban communities in cold temperate climates. As thermal resistance might be related to selective pressures and acclimation, it seems reasonable to assume that they may have a strong impact on local fauna and flora. In the present study, we simulated an in situ high amplitude heatwave and observed the community structure and the metabolism of Bugula neritina at two time-steps after the heatwave and compared them to control communities and individuals. Contrary to our expectations, the community structure remained vastly unaffected, as did the total metabolome of B. neritina. This shows that the community was able to resist the disturbance of the heatwave. Bugula neritina additionally showed a certain metabolic resilience as the already minor differences in the metabolome between control and the heatwave treatment diminished even further between the tested time steps.

Ecological succession involves the transition from opportunistic ephemeral species, which display a minimal variation in functional traits, to slow growing, more functionally diverse, perennial species. The present study aimed in measuring the functional effect of changes in the community structure through succession and to compare the timing of successional sequences in communities dominated by canopy-forming algae established at two levels of the emersion gradient in a rocky shore. Granite slabs were set at two tidal levels, in the Fucus vesiculosus and F. serratus areas, in February 2013. Communities settled on the slabs during the first year exhibited low Fucus density (approximate to 6 ind m-2), low taxa richness (approximate to 17 taxa) and low metabolic activity (gross primary production, GPP, about 100 mg C m-2 h-1) at both levels. Communities established on the slabs were similar to the surrounding communities for the 5 and 3 following years in the F. vesiculosus and F. serratus area respectively. Communities were then characterized by high Fucus density (approximate to 35 and 67 ind m-2), high taxa richness (approximate to 26 and 39 taxa) and high metabolic activity (GPP approximate to 350 and 550 mg C m-2 h-1). However, Fucus populations did not persist on slabs on which communities turned into limpet dominated, with low Fucus density, low taxa richness and low metabolic activity. 10 years after the slabs setting, limpet densities averaged 34 and 92 ind m-2. Given the long life-span of Fucus and Patella, the survey needs to be pursued to test for cyclical changes of dominance.

Redistribution of biodiversity represents a key challenge for understanding scales of spatial variation in natural marine communities. With increasing coastal urbanization, artificial structures are proliferating, with impacts on natural habitats, yet we have limited knowledge on the spatial scales of processes operating over their associated species assembly. This is exemplified by novel communities establishing along and around floating infrastructures, such as pontoons in marinas. In this study, we explored multi-scale patterns in the diversity and community structure of fouling seaweeds, invertebrates and fish communities associated with pontoons in 18 marinas, distributed along similar to 1000 km of coastline in NW France. With respect to the distribution of marinas across 3 distinct ecoregions, we predicted that their seaweed communities would follow spatial patterns reported in native communities from rocky shores. This hypothesis was poorly supported, and the variation among ecoregions (8%) was largely explained by the abundance of nonindigenous kelps. However, as anticipated, we observed important variability among and within marinas in all response variables (e.g. richness of sessile invertebrates and fish). These variations were related to contrasting sea surface temperature regimes among marinas, along with a number of explanatory variables (e.g. distance to marina entry). As also hypothesized, fouling and fish communities covaried with kelp biomass, although covariations were strengthened at the scale of the region and at the scale of the marina and pontoon when nonindigenous and native kelp were considered, respectively. Specificities in distributions and influences of foundation species in urban environments could be worth scrutinizing to inform their management.

We have followed the recovery of gaps produced either by harvesters or by scientists in stands of stalked barnacle (Pollicipes pollicipes) during two years in four regions of Europe (SW Portugal, Galicia and Asturias in Spain and Brittany in France; n = 423 gaps), which was extended to four years in Asturias (n = 252 gaps). The presence of adult conspecifics in the margins of the gaps increased by at least four times the probability of initiation of their recovery. After two years of follow-up in the four regions, 90

In order to address lack of data regarding coastal carbon budgets, we estimated the annual metabolic carbon budget of an intertidal rocky reef macroalgal community during emersion. This budget is based on direct in situ measurements during emersion and establishes the seasonal variations of the photosynthetic parameters of such a community. CO 2 fluxes were measured hourly to study the response of community gross primary productivity (GPP) to irradiance and the variation of GPP and community respiration (CR) over the emersion period at different times of the year. These were combined together with existing monthly measures of GPP and CR hourly rates to model the variations of these fluxes as a function of irradiance and the tidal cycle throughout an entire calendar year. Daily, monthly and annual values of GPP, CR and net primary productivity (NPP) were calculated with a relatively low sensitivity to any of the parameters used. While GPP fluxes show comparable orders of magnitude to those measured in other systems, higher CR fluxes lead to a heterotrophic system during emersion, both under measured (NPP = −299 gC m −2 year −1 ) and theoretical irradiances (NPP = −119 gC m −2 year −1 ). This heterotrophy is directly linked to the light availability, varying according to combined daily, tidal and seasonal cycles, and to temperature at the seasonal scale. Measurements performed in situ at the community scale integrated interactions that are otherwise absent at the individual scale. This gives access to aspects of the functioning that cannot be otherwise identified.

Urbanization of coastal habitats, often exemplified by harbors and marinas, has led to various ecological para-digms, questioning the functioning of these new ecosystems. In the present study we investigated, in a large Mediterranean harbor, whether spatial variation of pollution is present and if this variability drives the structure of the sessile community. We hypothesized locations to have significantly different communities, based on the assumption on the occurrence of environmental gradients of pollution that would constitute selective filters. Three distinct community types were identified in June, coinciding with spatially variable contaminants in sediments. We observed then an unexpected shift of the community between June and August associated to a sharp decrease in biodiversity and a decline of most species, masking the effects of local variation and thus leading to the homogenization of the biodiversity within the harbor. This shift coincided with successive heat -waves (the longest lasting 13 days over 25 degrees C, with a thermal peak at 28 degrees C) which might potentially be asso-ciated with a die-off in the harbor communities, regardless of location.

Urbanization of coastal habitats, of which harbors and marinas are the paragon, has led to various ecological paradigms about their functioning. Harbor infrastructures offer new hard substrata that are colonized by a wide variety of organisms (biofouling) including many introduced species. These structures also modify hydrodynamism and contaminant dispersal, leading to strong disturbance gradients within them. Differences in sessile community structure have previously been correlated to these gradients at small spatial scale (<100 m). Local adaptation might be involved to explain such results, but as correlation is not causation, the present study aims to understand the causal link between the environmental gradients and community structure through a reciprocal transplant experiment among three sites of a marina (inner, middle, entrance). Our results highlighted strong small-scale spatial variations of contaminants (trace metals, PCB, pesticides, and PAH) in sediments and animal samples which have been causally linked to changes in community composition after transplant. But historical contingency and colonization succession also play an important role. Our results provided strong evidence for local adaptation since community structure, respiration, and pollutant uptake in Bugula neritina, as well as the metabolomes of B. neritina and Ciona intestinalis were impacted by the transplant with a disadvantage for individuals transplanted from the entrance to the inner location. The here observed results may thus indicate that the disturbance gradient in marinas might constitute a staple for selecting pollutant-resistant species and populations, causing local adaptation. This highlights the importance of conducting further studies into small scale local adaptation.

Abstract Originating from Japan, the red macroalga Agarophyton vermiculophyllum colonizes saltmarshes from Europe and is invasive in mudflats from Brittany (France) where it creates a novel habitat with a high associated animal diversity. In Brittany, its particularity to bury in the mud, led us to wonder whether the buried fragments were still alive or just detritus. The seasonal phenology of buried fragments was monitored, together with the physiological state of fragments using Imaging-PAM fluorometry and respiration measurements. In parallel, metabolomic analyses allowed the analyses of the major intracellular metabolites. At depth in the mud, siltation is responsible for a fragmentation of the thallus and biochemical variations. A strong increase of antheraxanthin and zeaxanthin, chlorophyll-a and β-carotene was noticed while the R-Phycorythrine decreased. For osmolytes, we noted an alanine increase with siltation while floridoside decreased. No variation was noticed for isethionic acid and taurine. The C/N ratio was higher at the silt surface and decreased with siltation. Finally, The fragments are physiologically active; they present functional photosystems II and therefore do not consist of detrital material. Our study shows the ability of thalli to live in the mud to a depth of 12 cm. Fragmentation of the thallus is probably due to grazing intensity and bioturbation activity. Finally, the existence of small viable fragments deep in the mud, may represent a reserve biomass and considerably favors the propagation of Agarophyton vermiculophyllum, on the same site but may also allow a migration of the species through sediment transport.

Climate change constitutes a major challenge for marine urban ecosystems and ocean warming will likely strongly affect local communities. Non-Indigenous Species (NIS) have been shown to often have higher heat resistance than natives, but studies investigating how forthcoming global warming might affect them in marine urban environments remain scarce, especially in Situ studies. Here we used an in Situ warming experiment in a NW Mediterranean (warm temperate) and a NE Atlantic (cold temperate) marina to see how global warming might affect recruited communities in the near future. In both marinas, warming resulted in significantly different community structure, lower biomass, and more empty space compared to control. However, while in the warm temperate marina, NIS showed an increased surface cover, it was reduced in the cold temperate one. Metabolomic analyses on Bugula neritina in the Atlantic marina revealed potential heat stress experienced by this introduced bryozoan and a potential link between heat stress and the expression of a halogenated alkaloid, Caelestine A. The present results might indicate that the effects of global warming on the prevalence of NIS may differ between geographical provinces, which could be investigated by larger scale studies.

Understanding large-scale spatial and temporal patterns of marine populations is a central goal in ecology, which has received renewed attention under climate change. However, few studies explore the large-scale dynamics of populations using standardized protocols and during the same time frames. We studied the phenology and intensity of reproduction and recruitment for the intertidal stalked barnacle Pollicipes pollicipes over an European scale and described their potential linkages with environmental variables. This species supports profitable fisheries in the Iberian Peninsula (Spain and Portugal). In Brittany (France), we had observed a significant lower reproductive effort (long non-breeding season, short breeding period in summer) and low values of recruitment intensity. This pattern may be related to the fact that Brittany corresponds to the northern limit of the distribution of this species in continental Europe. On the Iberian Peninsula, the most different region was Galicia (Spain), with Asturias (Spain) and SW Portugal being more similar. In Galicia, we have observed a contradictory pattern characterized by the absence of a non-breeding period and by a shorter recruitment season than observed in other Iberian regions. Our results suggest that air temperature, SST and chlorophyll-a might be related to the variability in reproduction and recruitment patterns of P. pollicipes . Moreover, spring and early summer upwelling in SW Portugal and Galicia might be inhibiting recruitment in this period. At the northern limit, the expected increase in performance under climate change might facilitate the recovery of populations after exploitation, increasing the resilience of the resource to fishing pressure.

Drivers of successful introduction of exotic species remain a major headline in marine invasion biology. We ran two experiments aiming to disentangle the effects of abiotic factors like contaminants and the effect of predation on recruits' survival of one native and one alien ascidian species. A feeding experiment allowed us to monitor microscale variation of generalist fish predation, which varied significantly within a marina. We also monitored the in situ survival of lab-grown ascidians at three locations within the marina, half with predator cage exclusion. The survival of the native Ciona intestinalis was conjointly highly influenced by location and caging. We were able to identify a link between predation intensity exerted by mobile generalist macropredators and C. intestinalis survival, whereas none of the measured contaminants accounted for site variability of survival. The non-indigenous Styela clava had significant higher survival and biomass when uncaged, suggesting a positive effect of predation for this species. The natural in situ recruits of C. intestinalis showed higher biomass when caged and may have competed with lab-grown S. clava. Our results suggest that generalist fish predation may play a crucial role in the success of non-indigenous species due to facilitation through competitive release.

As a result of urbanization, coastal environments are being disturbed by various anthropogenic pressures. These are concentrated in harbor areas where the addition of artificial structures and the presence of pollutants seems to favor the settlement of non-indigenous species. Most studies on these organisms are often carried out in a single time window without integrating temporal variability. Here, we analyzed multi-year photographic data of marina communities taken from 3 experiments conducted between 2016 and 2019 in the same marina. These photographs were of recruitment plates placed at the inner, middle and entrance locations of the marina, permitting us to discern the community differences and the distribution of non-indigenous taxa between these 3 locations. Over the entire study period, the communities that grew at the entrance and the inner locations of the marina were always different. Non-indigenous taxa also appeared to be more prevalent in the inner location of the marina. Our results suggest that the presence of different environmental filters between the entrance and the inner location could explain these observations. We suggest this could be due to a pollution gradient, with high pollution at the inner location of the marina, and to competitive pressure exerted by the tunicate Ciona intestinalis at the marina entrance.

In January 2020, a stakeholder workshop was organized as a knowledge sharing strategy among European stalked barnacle fisheries. Management of this fishery differs greatly among regions and ranges from less organized and governed at large scales (>100 km, coasts of SW Portugal and Brittany in France) to highly participatory systems which are co-managed at small spatial scales (10's km and less, Galicia and Asturias). Discussions revealed that poaching is ubiquitous, hard to eradicate, and adapts to all types of management. The stakeholders identified some key management initiatives in the fight against poaching: granting professional harvesters with exclusive access to the resource, increasing social capital among harvesters through tenure systems (e.g. Territorial Use Rights in Fisheries) that empower them as stewards of their resource and intensification of surveillance with the active participation of the harvesters. Furthermore, increased cooperation between fishers associations and regional fisheries authorities, improved legal frameworks, adoption of new technologies and the implementation of market-based solutions can also help coping with this systemic problem.

Cycling of organic carbon in the ocean has the potential to mitigate or exacerbate global climate change, but major questions remain about the environmental controls on organic carbon flux in the coastal zone. Here, we used a field experiment distributed across 28° of latitude, and the entire range of 2 dominant kelp species in the northern hemisphere, to measure decomposition rates of kelp detritus on the seafloor in relation to local environmental factors. Detritus decomposition in both species were strongly related to ocean temperature and initial carbon content, with higher rates of biomass loss at lower latitudes with warmer temperatures. Our experiment showed slow overall decomposition and turnover of kelp detritus and modeling of coastal residence times at our study sites revealed that a significant portion of this production can remain intact long enough to reach deep marine sinks. The results suggest that decomposition of these kelp species could accelerate with ocean warming and that low-latitude kelp forests could experience the greatest increase in remineralization with a 9% to 42% reduced potential for transport to long-term ocean sinks under short-term (RCP4.5) and long-term (RCP8.5) warming scenarios. However, slow decomposition at high latitudes, where kelp abundance is predicted to expand, indicates potential for increasing kelp-carbon sinks in cooler (northern) regions. Our findings reveal an important latitudinal gradient in coastal ecosystem function that provides an improved capacity to predict the implications of ocean warming on carbon cycling. Broad-scale patterns in organic carbon decomposition revealed here can be used to identify hotspots of carbon sequestration potential and resolve relationships between carbon cycling processes and ocean climate at a global scale.

Accurate estimates of productivity of marine macrophytes are crucial to predict the consequences of invasive species expansions and climate-related range shifts on coastal ecosystem functioning and carbon cycling. We examined the potential impacts of climate-driven shifts in the relative abundances of foundation species within a temperate reef system on net primary productivity. Specifically, we estimated productivity rates of 3 co-occurring kelp species (Laminaria hyperborea , L. ochroleuca and Undaria pinnatifida) in contrasting regions of their ranges (centre, leading-edge and invasive, respectively) via in situ photorespirometry methods in Brittany, France. Lamina tissues of cold-temperate L. hyperborea and warm-temperate L. ochroleuca had similar rates of net productivity. The stipes of L. hyperborea , however, displayed much higher rates of productivity and respiration than L. ochroleuca , likely due to the dense macroalgal epiphytes colonising their surface. Our results suggest that replacement of L. hyperborea by L. ochroleuca in the NE Atlantic due to increased dominance or further range expansion of this warm-temperate species might lead to reduced net rates of productivity as a result of increased lamina respiration and reduced photosynthetic capacity of stipes. The invasive kelp U. pinnatifida had high rates of net productivity at saturating light levels (294 µmol O 2 g -1 dry weight h -1 ), 3 times higher than any kelp species ever incubated in situ , helping to explain its high success as an invader. We show that shifts in the distributions and relative abundances of seemingly similar foundation species may lead to subsequent changes in net metabolic balance.

Maerl beds are composed of unattached red calcareous coralline algae. When located in shallow ecosystems, these calcareous macroalgae provide substrates for the development of fleshy epiphytic macroalgae, which contribute to the productivity of the maerl beds. To assess the importance of their contribution, we estimated the primary production of the main taxa of fleshy epiphytic macroalgae (Solieria chordalis or Rhodomelaceae), growing in 2 distinct Lithothamnion corallioides maerl beds in the Bay of Brest (Brittany, France), characterized by different depths and incident irradiances. We estimated epiphytic algal photosynthetic parameters derived from photosynthesis-irradiance curves calculated from incubations in photo-respirometry chambers at different irradiances and in the dark. A comparison with results previously obtained in L. corallioides showed that in the 2 studied maerl beds there were no differences between maerl and its fleshy epiphytic macroalgae in terms of photo-acclimation to low irradiances. However, fleshy epiphytic macroalgae had higher photosynthetic efficiencies and photosynthetic rates per unit of biomass or chlorophyll a than the maerl species. Estimations of net primary production per surface area of maerl bed indicated that fleshy epiphytic macroalgae account for 25% of maerl bed productivity. Interactions between L. corallioides and its fleshy epiphytic macroalgae may affect their respective contributions. In the deepest maerl beds, shading by fleshy epiphytic macroalgae may have a detrimental impact on L. corallioides net primary production, whereas in the shallowest maerl beds, fleshy epiphytic macroalgae may protect maerl from photoinhibition under high irradiances.

Kelps are dominant primary producers in temperate coastal ecosystems. Large amounts of kelp biomass can be exported to the seafloor during the algal growth cycle or following storms, creating new ecological niches for the associated microbiota. Here, we investigated the bacterial community associated with the kelp Laminaria hyperborea during its accumulation and degradation on the seafloor. Kelp tissue, seawater and sediment were sampled during a 6-month in situ experiment simulating kelp detritus accumulation. Evaluation of the epiphytic bacterial community abundance, structure, taxonomic composition and predicted functional profiles evidenced a biphasic succession. Initially, dominant genera (Hellea, Litorimonas, Granulosicoccus) showed a rapid and drastic decrease in sequence abundance, probably outcompeted by algal polysaccharide-degraders such as Bacteroidia members which responded within 4 weeks. Acidimicrobiia, especially members of the Sva0996 marine group, colonized the degrading kelp biomass after 11 weeks. These secondary colonizers could act as opportunistic scavenger bacteria assimilating substrates exposed by early degraders. In parallel, kelp accumulation modified bacterial communities in the underlying sediment, notably favouring anaerobic taxa potentially involved in the sulfur and nitrogen cycles. Overall, this study provides insights into the bacterial degradation of algal biomass in situ, an important link in coastal trophic chains.