Search

Through a field experiment, we show that a predator has negative nonconsumptive effects (NCEs) on different life-history stages of the same prey species. Shortly before the recruitment season of the barnacle Semibalanus balanoides (spring), we established experimental cages in rocky intertidal habitats in Nova Scotia, Canada. The cages were used to manipulate the presence and absence of dogwhelks, Nucella lapillus, the main predators of barnacles. At the centre of each cage, we installed a tile where barnacle pelagic larvae could settle and the resulting recruits grow. Mesh prevented caged dogwhelks from accessing the tiles, but allowed waterborne dogwhelk cues to reach the tiles. During the recruitment season, barnacle larvae settled preferentially on tiles from cages without dogwhelks. In the fall, at the end of the dogwhelk activity period and once the barnacle recruits had grown to adult size, barnacle body mass was lower in the presence of dogwhelks. This limitation may have resulted from a lower barnacle feeding activity with nearby dogwhelks, as found in a previous study. The observed larval and adult responses in barnacles are consistent with attempts to decrease predation risk. In the fall, dogwhelk cues also limited barnacle reproductive output, a possible consequence of the limited growth of barnacles. Overall, the results of this study suggest that a predator might influence trait evolution in a prey mediated by NCEs on different life-history stages.

Multiple predators can additively or synergistically affect populations of shared prey. During the last 15 y, the Helgoland breeding population of the avian mussel predator S. molissima increased 10-fold, while blue mussel (Mytilus edulis) abundance decreased accordingly on the rocky intertidal shores of Helgoland. In a 16-month field experiment, we tested whether the combined predation impact of benthic and avian predators (= control) resulted in lower blue mussel survivorship than through the exclusion of avian predators alone and compared this to the overall predation effect (= complete exclusion cage). Predation effects were assessed for initially small (22 – 39 mm) and large M. edulis (40 – 60 mm), matching preferred and dismissed size ranges, respectively, of S. mollissima and the most abundant benthic predator, the green crab Carcinus maenas. Blue mussel survivorship was quantified in September 2014 and May 2015, i.e. just before crabs and common eiders generally disappear from and after they return to the intertidal, respectively, and, finally, again in September 2015. Survivorship of both, small and large M. edulis was not significantly different between control plots and plots where avian predators were excluded, but was in both treatments significantly lower than in plots where all predators were excluded with complete cages. This pattern was consistently apparent at each of the three sampling events. Our results suggest that the recent decline of the intertidal blue mussel population may have happened independently of the concomitant arrival of an avian mussel predator.

Recent studies have shown that predator chemical cues can limit prey demographic rates such as recruitment. For instance, barnacle pelagic larvae reduce settlement where predatory dogwhelk cues are detected, thereby limiting benthic recruitment. However, adult barnacles attract conspecific larvae through chemical and visual cues, aiding larvae to find suitable habitat for development. Thus, we tested the hypothesis that the presence of adult barnacles (Semibalanus balanoides) can neutralize dogwhelk (Nucella lapillus) nonconsumptive effects on barnacle recruitment. We did a field experiment in Atlantic Canada during the 2012 and 2013 barnacle recruitment seasons (May–June). We manipulated the presence of dogwhelks (without allowing them to physically contact barnacles) and adult barnacles in cages established in rocky intertidal habitats. At the end of both recruitment seasons, we measured barnacle recruit density on tiles kept inside the cages. Without adult barnacles, the nearby presence of dogwhelks limited barnacle recruitment by 51%. However, the presence of adult barnacles increased barnacle recruitment by 44% and neutralized dogwhelk nonconsumptive effects on barnacle recruitment, as recruit density was unaffected by dogwhelk presence. For species from several invertebrate phyla, benthic adult organisms attract conspecific pelagic larvae. Thus, adult prey might commonly constitute a key factor preventing negative predator nonconsumptive effects on prey recruitment.

Predators may have nonconsumptive effects (NCEs) on prey populations mediated by chemical cues detected by prey. We experimentally investigated dogwhelk (Nucella lapillus) NCEs on intertidal barnacle (Semibalanus balanoides) recruit density in Nova Scotia, Canada. Under a moderate abundance of coastal phytoplankton (food for barnacle larvae and recruits), barnacle recruitment was moderate and the nearby presence of dogwhelks limited barnacle recruit density at the end of the recruitment season. Under a high phytoplankton abundance, barnacle recruitment was high and neutralized dogwhelk NCEs on barnacle recruit density, likely through the chemical attraction that recruits exert on larvae seeking settlement.

Grazing-induced plant defences that reduce palatability to herbivores are widespread in terrestrial plants and seaweeds, but they have not yet been reported in seagrasses. We investigated the ability of two seagrass species to induce defences in response to direct grazing by three associated mesograzers. Specifically, we conducted feeding-assayed induction experiments to examine how mesograzer-specific grazing impact affects seagrass induction of defences within the context of the optimal defence theory. We found that the amphipod Gammarus insensibilis and the isopod Idotea chelipes exerted a low-intensity grazing on older blades of the seagrass Cymodocea nodosa, which reflects a weak grazing impact that may explain the lack of inducible defences. The isopod Synischia hectica exerted the strongest grazing impact on C. nodosa via high-intensity feeding on young blades with a higher fitness value. This isopod grazing induced defences in C. nodosa as indicated by a consistently lower consumption of blades previously grazed for 5, 12 and 16 days. The lower consumption was maintained when offered tissues with no plant structure (agarreconstituted food), but showing a reduced size of the previous grazing effect. This indicates that structural traits act in combination with chemical traits to reduce seagrass palatability to the isopod. Increase in total phenolics but not in C:N ratio and total nitrogen of grazed C. nodosa suggests chemical defences rather than a modified nutritional quality as primarily induced chemical traits. We detected no induction of defences in Zostera noltei, which showed the ability to replace moderate losses of young biomass to mesograzers via compensatory growth. Our study provides the first experimental evidence of induction of defences against meso-herbivory that reduce further consumption in seagrasses. It also emphasizes the relevance of grazer identity in determining the level of grazing impact triggering resistance and compensatory response

Arctic fjords host a diverse seaweed community forming the base of the benthic foodweb and providing habitat and shelter for a vast diversity of associated fauna. Seaweed model species as well as seaweed communities are intensively studied with reference to their general adaptive and functional traits, as well as their responses to global environmental change. Our long-term project ats Svalbard aims at a holistic understanding of seaweed ecosystem function spanning from the environmental control of gene expression to energy flow through trophic levels. Research is currently focusing on the sugar kelp Saccharina latissima and the wing kelp Alaria esculenta as abundant model species under a set of combined stressors such asthe combined stressors elevated UV-B radiation and temperature or increased sedimentation and grazing. In addition the responses of seaweeds to increased CO2 are addressed. In the frame of this global change scenario species-specific acclimation patterns are studied aton the physiological levelbase and species competition at the community level. Both approaches intendin order to predict shifts in the competitive strength of habitat engineeringa respective species, potentially resulting in a changing seaweed community. Comparative community analyses conducted in 1996-98 and 2012-2014 indicate a considerable change in seaweed biomass, a change in kelp depth limits and a change in species richness at low depth at the study site off Hansneset/Kongsfjord, Spitsbergen, but no obvious biodiversity change all possibly correlated to the recent warming of winters. The seaweed biomass maximum was shifted from 5 to 2.5m depth and overall biomass increased. Future surveys are needed to separate climate related signals against a background of high interannual variability.

We investigated the non-consumptive effects (NCEs) of predatory dogwhelks (Nucella lapillus) on intertidal barnacle (Semibalanus balanoides) recruitment through field experiments on the Gulf of St. Lawrence coast and the Atlantic coast of Nova Scotia, Canada. We studied the recruitment seasons (May–June) of 2011 and 2013. In 2011, the Gulf coast had five times more nearshore phytoplankton (food for barnacle larvae and recruits) during the recruitment season and yielded a 58 % higher barnacle recruit density than the Atlantic coast at the end of the recruitment season. In 2013, phytoplankton levels and barnacle recruit density were similar on both coasts and also lower than for the Gulf coast in 2011. Using the comparative–experimental method, the manipulation of dogwhelk presence (without allowing physical contact with prey) revealed that dogwhelk cues limited barnacle recruitment under moderate recruit densities (Atlantic 2011/2013 and Gulf 2013) but had no effect under a high recruit density (Gulf 2011). Barnacle recruits attract settling larvae through chemical cues. Thus, the highest recruit density appears to have neutralized dogwhelk effects. This study suggests that the predation risk perceived by settling larvae may decrease with increasing recruit density and that prey food supply may indirectly influence predator NCEs on prey recruitment.

The relationship between biodiversity and stability of marine benthic assemblages was investigated through meta-analyses using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006; ranging from 5 to >250 months) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) over different European marine systems (North Atlantic and western Mediterranean). Stability was measured by a lower variability in time, and variability was estimated as temporal variance of species richness, total abundance (density or % cover) and community structure (using Bray-Curtis dissimilarities on species composition and abundance). Stability generally decreased with species richness. Temporal variability in species richness increased with the number of species at both quadrat (<1 m2) and site (100 m2) scales, while no relationship was observed by multivariate analyses. Positive relationships were also observed at the scale of site between temporal variability in species richness and variability in community structure with evenness estimates. This implies that the relationship between species richness or evenness and species richness variability is slightly positive and depends on the scale of observation. Thus, species richness does not stabilize temporal fluctuations in species number, rather species rich assemblages are those most likely to undergo the largest fluctuations in species numbers and abundance from time to time. Changes within community assemblages in terms of structure are, however, generally independent of biodiversity. Except for sedimentary and rock pool habitats, no relationship was observed between temporal variation of total abundances and diversity at either scale. Overall, our results emphasise that the relation between species richness and species-level measures of temporal variability depend on scale of measurements, type of habitats and the marine system (North Atlantic and Mediterranean) considered.

In many temperate regions, brown macroalgae fulfil essential ecosystem services such as the provision of structure, the fixation of nutrients and carbon, and the production of biomass and oxygen. Their populations in many regions around the globe have declined and/or spatially shifted in recent decades. In this review we highlight the potential global and regional drives of these changes, describe the status of regionally particularly important brown macroalgal species, and describe the capacity of interactions among abiotic and biotic factors to amplify or buffer environmental pressure on brown macroalgae. We conclude with a consideration of possible management and restoration measures.

This study aimed to reveal the dynamics of inducible anti-herbivory traits in the brown seaweed Fucus vesiculosus, in response to grazing by the isopod Idotea baltica. As the molecular basis of defence induction in seaweeds is poorly understood, a transcriptomic approach was used to gain insight into cellular processes underlying defence induction and thus promote the mechanistic understanding of anti-herbivory responses in seaweeds. In a 27 day feeding-assayed induction experiment, temporal patterns of the induced anti-herbivory resistance of F. vesiculosus were assessed under laboratory conditions. Feeding assays were performed at three day intervals, using fresh and reconstituted food. Microarray hybridizations investigating the expression of genes 3 days before, as well as at the same time as, feeding assays revealed a decreased palatability of previously grazed F. vesiculosus pieces compared with non-grazed control pieces. Despite permanent exposure to grazers, F. vesiculosus palatability varied over time. Non-grazed F. vesiculosus pieces were significantly preferred to grazed pieces after 18 and again after 27 days of previous grazing, while their relative palatability for isopods was comparable at all other times during the experiment. Relative to controls, 562/402 genes were ≥ 1.5-fold up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when induction of defences was detected in feeding assays. Massive reprogramming of the regulatory expression orchestra (translation, transcription) as well as up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defence and stress response was found. At the same time, down-regulation of photosynthesis was observed in grazed seaweed pieces. This study suggests a high level of temporal variability in induced anti-herbivory traits of F. vesiculosus and reveals increased expression of genes with putative defensive functions in conjunction with the reallocation of re

Seaweeds are known to change their phenotype in response to wave-exposure. Shifts in shape or texture due to phenotypic plasticity may affect subsequent interactions between seaweeds and other species. In two transplantation experiments, we tested the ability of the brown seaweed Fucus vesiculosus to acclimate to different levels of wave-exposure and whether this acclimation affected its consumption by different grazer species. In different years, a transplantation of F. vesiculosus between exposed and sheltered sites provoked a rapid shift of apical thallus toughness, measured as puncture strength, towards values found in conspecifics that remained throughout the experiment at the respective recipient site (= replants). The time needed to significantly change thallus toughness was 9 times shorter in F. vesiculosus that were transplanted from the sheltered to the exposed site (8 days) than in the opposite direction (i.e. 72 days). Prior to transplantation, both the North Sea isopod Idotea baltica and the amphipod Echinogammarus marinus consumed significantly more sheltered-site than exposed-site apical pieces of F. vesiculosus. This pattern was confirmed with F. vesiculosus and I. baltica from the Baltic Sea population. In contrast, no discrimination was apparent when the North Sea grazers could chose between reconstituted food made of either sheltered-site or exposed-site F. vesiculosus. At the end of the transplantation experiment, grazers consumed equal amounts of transplanted and replanted F. vesiculosus. Results indicate that (i) wave exposure altered morphological rather than non-morphological properties (ii), a toughening of tissue with an increase of exposure is faster than the relaxation of toughness with decreasing exposure and (iii) trait plasticity modified the suitability of F. vesiculosus as food for mandible-bearing grazer species. Thus, grazing impact was reduced when wave exposure increased; possibly offering seaweeds an opportunity to trade-off cos

The effects of omnivory on population ecology are rarely studied, although scavenging can be expected in species that are obligated herbivorous to supplement dietary needs for improving their fitness and/or performance. In one field and two laboratory experiments scavenging effects on growth and reproductive success (mating frequency, daily number of eggs per female, hatching rate) of and the attraction to carrion were investigated for the intertidal herbivorous periwinkle Littorina littorea. In the field, M. edulis with cut adductor muscles (= opened; representing carrion) were significantly more frequently contacted by L. littorea than either intact M. edulis or Ulva lactuca, with no significant differences in contact frequency between the latter two. In the laboratory, L. littorea that were exclusively offered opened M. edulis grew significantly less than conspecifics that were either offered U. lactuca alone or that were kept on a mixed diet (= opened mussel and U. lactuca). Regarding reproductive output, L. littorea produced fewer eggs when offered opened M. edulis than conspecifics that were either kept on a mixed diet or exclusively on an U. lactuca diet. Mating frequency and hatching success of eggs was not significantly different between L. littorea kept on the three diets. Our results confirm a NW Atlantic study showing that L. littorea was attracted to carrion. Yet, missing significant differences in growth and reproductive output of periwinkles that were or were not allowed to scavenge (= mixed diet vs. exclusively U. lactuca fed) suggests neutral scavenging effects on periwinkle fitness and performance. Perhaps, scavenging by periwinkles could be important at higher levels of ecological organization, due to an increase in the frequency of interspecific interactions and/or a facilitated flow of energy and matter, all of which should add on stabilizing food web structure.

Some seaweed species have been shown to release water-borne cues after herbivore attack, for example, to attract natural enemies of the herbivore. These cues may also be sensed by neighboring seaweeds and used to adjust their defenses in anticipation of a possible herbivore attack. Several studies indicated information transfer between seaweed individuals in the past, including the brown seaweed Fucus vesiculosus. Previous work showed induction of defenses in F. vesiculosus in response to water-borne cues released by isopod-grazed conspecifics. In contrast, another study on induced responses after exposure to cues from isopod-grazed neighbors using the same seaweed species yielded contradictory results. This study reassessed the ability of F. vesiculosus individuals to sense water-borne cues released by isopod-grazed neighbors in a series of experiments that monitored F. vesiculosus palatability in response to direct grazing by Idotea baltica and water-borne cues from isopod-grazed neighbors relative to unmanipulated seaweed pieces. Two-choice feeding assays were conducted with both fresh and reconstituted seaweed pieces. Direct grazing by I. baltica induced a chemical defense in F. vesiculosus, confirming results of previous studies. In contrast, evidence for increased herbivore resistance in seaweed pieces that were located downstream of isopod-grazed F. vesiculosus could not be provided. The lack of defense induction in response to grazing of conspecific neighbors may be explained by the environmental conditions and the scattered distribution of F. vesiculosus individuals in the intertidal zone of Helgoland, which may render resource investment in the emission and/or response to water-borne cues at this site unprofitable.

Herbivory is a key factor for controlling seaweed biomass and community structure. To cope with grazers, constitutive and inducible defenses have evolved in macroalgae. Inducible chemical defenses show grazer-specificity and, at the same time, have the potential to mediate interactions among different herbivores. Furthermore, temporal variations in defense patterns, which may adjust antiherbivory responses to grazing pressure, were reported in two brown seaweeds. However, underlying cellular processes are only rudimentarily characterized. To investigate the response of Fucus vesiculosus (L.) to periwinkle (Littorina obtusata) grazing, feeding assays were conducted at several times during a 33 d induction experiment. Underlying cellular processes were analyzed through gene expression profiling. Furthermore, direct processes driving the antiherbivory response to periwinkle grazing and indirect effects on another herbivore, the isopod Idotea baltica, were elucidated. F. vesiculosus showed multiple defense pulses in response to periwinkle grazing, suggesting a high level of temporal variability in antiherbivory traits. Defense induction was accompanied by extensive transcriptome changes. Approximately 400 genes were significantly up-/down-regulated relative to controls, including genes relevant for translation and the cytoskeleton. Genes involved in photosynthesis were mostly downregulated, while genes related to the respiratory chain were up-regulated, indicating alterations in resource allocation. The comparison of genes regulated in response to isopod (previous study) and periwinkle grazing suggests specific induction of several genes by each herbivore. However, grazing by both herbivores induced similar metabolic processes in F. vesiculosus. These common defense-related processes reflected in strong indirect effects as isopods were also repelled after previous grazing by L. obtusata.

The trophic interactions between herbivores and seaweeds have been scarcely studied for the Kongsfjorden ecosystem, despite the dominance of seaweeds in abundance and biomass in hard-bottom habitats. Knowledge on trophic seaweed-grazer interactions is necessary to comprehensively understand and ultimately model the structure of an Arctic food web. In recent years, data on seaweed consumption and indirectly on food preferences of herbivores were gathered. Moreover, observational and manipulative experiments were conducted in the field and laboratory, addressing the indirect effects between sea urchins and two seaweed species and how these affect behavioural urchin responses as well as community structure of hard-bottom habitats. This data could enter, for instance, a review on “marine food webs” listed on the tentative topic list for the workshop.

Ecosystems are under pressure from multiple human disturbances whose impact may vary depending on environmental context. We experimentally evaluated variation in the separate and combined effects of the loss of a key functional group (canopy algae) and physical disturbance on rocky shore ecosystems at nine locations across Europe. Multivariate community structure was initially affected (during the first three to six months) at six locations but after 18 months, effects were apparent at only three. Loss of canopy caused increases in cover of non-canopy algae in the three locations in southern Europe and decreases in some northern locations. Measures of ecosystem functioning (community respiration, gross primary productivity, net primary productivity) were affected by loss of canopy at five of the six locations for which data were available. Short-term effects on community respiration were widespread, but effects were rare after 18 months. Functional changes corresponded with changes in community structure and/or species richness at most locations and times sampled, but no single aspect of biodiversity was an effective predictor of longer-term functional changes. Most ecosystems studied were able to compensate in functional terms for impacts caused by indiscriminate physical disturbance. The only consistent effect of disturbance was to increase cover of non-canopy species. Loss of a canopy algae temporarily reduced community resistance to disturbance at only two locations and at two locations actually increased resistance. Resistance to disturbance-induced changes in gross primary productivity was reduced by loss of canopy algae at four locations. Location-specific variation in the effects of the same stressors argues for flexible frameworks for the management of marine environments. These results also highlight the need to analyse how species loss and other stressors combine and interact in different environmental contexts.

Barnacles are dominant sessile invertebrates on many rocky shores worldwide. Hence, investigating the factors that affect their recruitment is important. Through field experiments done on the Atlantic coast of Canada, we investigated interspecific and intraspecific relationships affecting intertidal barnacle recruitment. Specifically, we evaluated the effects of seaweed canopies (Ascophyllum nodosum) and adult barnacles (Semibalanus balanoides) on the density of barnacle recruits at the end of the recruitment season. The effects of three canopy treatments on barnacle recruitment and understory environmental conditions allowed us to identify positive and negative effects of canopies. At mid-intertidal elevations subjected to a moderate wave action, we found that, during high tides, the flexible algal fronds damage wire sensors established on the substrate (whiplash effect) and limit barnacle recruitment. However, at low tide, algal canopies limit water loss and temperature extremes and enhance barnacle recruitment in understory habitats. The net effects of algal canopies on barnacle recruitment, however, were neutral, as the positive and negative influences balanced out. By manipulating the abundance of adult barnacles under the seaweed canopies, we found that adult barnacles enhance barnacle recruitment, likely due to the known attraction that adults exert on larvae seeking settlement and to the absence of post-settlement events that could otherwise have blurred such effects by the adults. The presence of adult barnacles, however, did not protect developing recruits from canopy whiplash effects. By understanding the contrasting influences that intertidal algal canopies have on understory abiotic conditions and barnacle recruitment, our ability to predict net canopy effects depending on the relative degree of physiological (e.g., high vs. low intertidal zone) and physical (e.g., sheltered vs. exposed shores) stresses should increase. This study also suggests that rec

Anti-herbivory defenses support persistence of seaweeds. Little is known, however, about temporal dynamics in the induction of grazer-deterrent seaweed traits. In two induction experiments consumption rates of the periwinkle Littorina obtusata (L.) on the brown seaweed Ascophyllum nodosum (L.) Le Jol. were measured in 3 day intervals. Moreover, changes in palatability of directly grazed A. nodosum were tested every 3 days with feeding assays using fresh and reconstituted seaweed pieces. Likewise, assays with fresh A. nodosum assessed changes in seaweed palatability in response to water-borne cues from nearby grazed conspecifics. Consumption rates of L. obtusata varied significantly during the 27 day induction phase of each experiment. Also, direct grazing by L. obtusata lowered palatability of fresh and reconstituted A. nodosum pieces to conspecific grazers after 15 days as well as after 6 and 12 days, respectively. Furthermore, after 12, 18, and 24 days fresh A. nodosum located downstream of L. obtusata-grazed conspecifics was significantly less palatable than A. nodosum located downstream of ungrazed conspecifics. Changes in L. obtusata consumption rates and A. nodosum palatability during both induction experiments suggest temporal variation of grazer-deterrent responses, which may complicate experimental detection of inducible anti-herbivory defenses.

Grazing by the isopod Idotea baltica induces chemical defenses in the brown seaweed Fucus vesiculosus. A combination of a 33 day induction experiment, feeding choice assays and functional genomic analyses was used to investigate temporal defense patterns and to correlate changes in palatability to changes in gene expression. Despite permanent grazing, seaweed palatability varied over time. Controls were significantly more consumed than grazed pieces only after 18 and 27 days of grazing. Relative to controls, 562/402 genes were up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when defense induction was detected. Reprogramming of the regulative expression orchestra (translation, transcription), up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defense and stress response, as well as downregulation of photosynthesis was found in grazed seaweed. These findings indicate short-term temporal variation in defenses and that modified gene expression patterns arise at the same time when grazed seaweed pieces show reduced palatability. Several genes with putative defensive functions and cellular processes potentially involved in defence, such as reallocation of resources from primary to secondary metabolism, were revealed

Ecosystems are under pressure from multiple human disturbances whose impact may vary depending on environmental context. We experimentally evaluated variation in the separate and combined effects of the loss of a key functional group (canopy algae) and physical disturbance on rocky shore ecosystems at nine locations across Europe. Multivariate community structure was initially affected (during the first three to six months) at six locations but after 18 months, effects were apparent at only three. Loss of canopy caused increases in cover of non-canopy algae in the three locations in southern Europe and decreases in some northern locations. Measures of ecosystem functioning (community respiration, gross primary productivity, net primary productivity) were affected by loss of canopy at five of the six locations for which data were available. Short-term effects on community respiration were widespread, but effects were rare after 18 months. Functional changes corresponded with changes in community structure and/or species richness at most locations and times sampled, but no single aspect of biodiversity was an effective predictor of longer-term functional changes. Most ecosystems studied were able to compensate in functional terms for impacts caused by indiscriminate physical disturbance. The only consistent effect of disturbance was to increase cover of non-canopy species. Loss of canopy algae temporarily reduced community resistance to disturbance at only two locations and at two locations actually increased resistance. Resistance to disturbance-induced changes in gross primary productivity was reduced by loss of canopy algae at four locations. Location-specific variation in the effects of the same stressors argues for flexible frameworks for the management of marine environments. These results also highlight the need to analyse how species loss and other stressors combine and interact in different environmental contexts.