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Marine macroalgae are key components of rocky shores and provide habitat, food, and shelter for numerous organisms while marine herbivores play an important role in regulating the biomass of seaweeds. To persist in benthic communities, traits evolved in seaweeds to avoid, tolerate, or deter herbivory. An increasing amount of literature confirms that seaweeds often respond to grazers with the induction of chemical defenses. In contrast to terrestrial systems, little is known about temporal dynamics and underlying molecular processes of inducible defenses in seaweeds. A 33 day long induction experiment assessed patterns in temporal variation of anti-herbivory defenses in the brown alga Fucus vesiculosus (bladder wrack) in response to grazing by the isopod Idotea baltica. Every 3 days, two-choice feeding assays with naïve grazers tested whether defenses were induced. Selected samples were used for RNA extraction and microarray hybridizations to determine changes in gene expression patterns. We showed that Fucus palatability varied over time with controls being significantly more consumed than grazed seaweed pieces after 18 and 27 days of previous grazing in the induction period. We observed a significant change in the gene expression of grazed Fucus compared to controls. Isopod grazing up-regulated 536 genes, 340 genes were found to be down-regulated. 21% of all regulated genes were annotated using different databases (e.g. NCBI sequence database, Swiss-Prot protein knowledgebase) and allocated to KOG (Clusters of eukaryotic Orthologous Groups) categories. Isopod grazing and consequential induction of anti-herbivory defenses yielded in up-regulation of the categories ‘intracellular trafficking, secretion, and vesicular transport’ and ‘defense mechanisms’, whereas transcripts involved in photosynthesis were strongly down-regulated. Our data revealed modified gene expression patterns that occurred simultaneously to a reduced palatability in consequence of isopod grazing.

Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting the temporal stability of natural communities. Using the model of European intertidal rocky shore assemblages and collating 17 datasets, we investigated how the strength of these stability-enhancing mechanisms varies with latitude and how it can be altered by the loss of habitat-formers (e.g. canopy-forming macroalgae). Community stability decreased with increasing latitude, mostly as a consequence of a greater synchronization of species fluctuations. Statistical averaging and overyielding (i.e. richness effects) promoted stability, but their strength did not vary with latitude. The experimental removal of macroalgal canopies caused a strengthening of the statistical averaging effect that was consistent across the latitudinal gradient investigated. Nonetheless, the loss of canopies depressed stability by enhancing the synchronization of species fluctuations on southernmost shores, while it had weak effects on shores at higher latitudes. Variation in life-history traits among canopy-forming species and/or in prevailing environmental conditions across a gradient of latitude could underlie variable effects of habitat-formers on species fluctuations. Our study shows i) that the stability of intertidal assemblages and strength of compensatory dynamics varies with latitude, ii) that canopy-forming macroalgae, exerting a strong control on understorey species, can influence the strength of compensatory dynamics and iii) that biological forcing (i.e. facilitation) can be as important as environmental forcing in enhancing the synchronization of species fluctuations.

Future levels in ultraviolet-B (UVB) radiation are expected to increase directly due to stratospheric ozone depletion and under water indirectly by, for example, global warming effects on DOC concentrations, altered trophic interactions in the plankton, or reduced eutrophication. While detrimental UV effects have been reported at the cellular level, little to nothing is known about community-wide effects of ambient and future UVB radiation. In a 4-month field experiment, the ambient UV regime was (i) reduced by cut-off filters which removed either UVB or total UV from the solar spectrum or (ii) increased to predicted future levels by UVB lamps. To allow relating the effects of present and future UV regimes to another important ecological control of community structure and diversity in subtidal marine habitats, consumer effects were quantified by an exclusion treatment under ambient light regimes. Ambient UV regimes did not affect community structure, biomass accrual, and diversity. In contrast, under enhanced UVB levels, the dominance of the competitively superior blue mussels increased and species richness and biomass accrual decreased. Species composition of the assemblages differed between the two UV regimes. Effects of enhanced UVB radiation and of consumption on biomass accrual, diversity, and structure of the community were comparable in magnitude and timing, but of opposite direction. In contrast, the effects of enhanced UVB radiation on growth and abundance of mussels were in the same direction, but shorter and weaker than consumer effects. Most UV effects were transitory and vanished within the first 2 months of succession. Our results indicate that present and future UVB levels may be of limited importance and not stronger in effect size than other ecological controls in structuring the shallow-water low-diversity macrobenthic communities in temperate regions.

Disturbance and productivity are often cited as the main factors determining temporal and spatial patterns in species distribution and the diversity of communities. A field experiment was conducted to test the role of these factors in the structuring of early successional fouling communities in a nutrient limited system at the south coast of Madeira Island. Macro-benthic sessile communities, established on artificial settlement substrata, were manipulated and surveyed over a 9-week period. We applied mechanical disturbances of four different frequencies crossed with three levels of inorganic nutrient enrichment. Fertilization enhanced community diversity by favouring the establishment and growth of macroalgae. Disturbance reduced diversity by eliminating species – but only at the highest nutrient level. This is explained by a multiple-stressor model; species most sensitive to nutrient deficiency (only present in the highest enrichment treatment) were simultaneously the most sensitive to disturbance

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a 'sensu lato' concept, introduced here. This includes all species which have been considered to be 'Laminaria' before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general.

Assessing patterns of species distribution and abundance is important to understand the driving processes of, and predict future changes in, biodiversity. To this date, ecological studies have been mainly designed to investigate the effects of the mean magnitude of predictor variables, although ecological factors naturally vary in space and time. In a nine month long field experiment, we tested the effects of different temporal patterns (regular, lowly and highly irregular) in biomass removal (=disturbance event) on the diversity, species composition, and biomass accrual of macrobenthic assemblages grown on 15 × 15 cm2 PVC-panels. For each pattern of disturbance, disturbance events were timed at three sequences to control for possible confounding effects with recruitment patterns. Disturbance intensity was kept identical among treatments. Assemblages developed in the absence of disturbance for 3 months prior to a 150-day manipulation period, during which the biomass from 20% of the panel area was removed at each of ten disturbance events. Additional undisturbed settlement panels were deployed in the field to assess monthly recruitment rates and species succession over a one year period. Disturbance (i) reduced biomass and total species cover, (ii) changed species composition during the first half of the manipulation period significantly, and (iii) was without effect on species richness and evenness. Irregular disturbance regimes enhanced the abundance of the ascidian Ciona intestinalis, biomass accrual, and total species cover of assemblages relative to the regular disturbance regime, but had either no or only transient effects on diversity and species composition, respectively. Neither the degree of irregularity in disturbance nor the sequence of disturbance events affected any of the response variables significantly. Recruitment of species was strongly seasonal with almost only diatoms recruiting during winter, while recruitment was most intense during summer. Our

1 Several theoretical models predict under what conditions maximum species diversity can be maintained, and they are often used to develop effective ecosystem management plans. 2 Two models that are currently used to predict patterns of species diversity were empirically tested in marine subtidal benthic communities of different successional stages. 3 The two models were: the interactive effects of nutrient availability and disturbance frequency proposed by Kondoh (2001; Proceedings of the Royal Society London B, 268, 269–271), and the intermediate disturbance hypothesis (IDH) proposed by Connell (1978; Science, 199, 1302–1310). 4 Interactive effects were found to be transient and only occurred in the older communities, while the unimodal pattern suggested by the IDH was not supported in either successional stage. 5 It is concluded that these models are very general and thus lack sufficient explanatory power. Both models require a number of specific prerequisites for maximum diversity to be found, and though applicable in many different ecosystems they need to be refined as tools in order that they can be effectively used in habitat management plans.

Local dynamics such as resource enhancement (e.g. nutrient supply) and stochastic events of destruction (disturbances that provide new space) are hypothesized to counteractively affect species diversity and composition.We tested the independent and interactive effects of nutrients and disturbance on the development of assemblages of epibiota attached to vertical surfaces in an oligotrophic system. Nutrient concentrations were manipulated at three levels (ambient, medium and high) while disturbance was manipulated by removing biomass at seven frequencies (0x, 2x, 3x, 4x, 5x, 7x, 12x). Nutrient and disturbance regimes had opposing effects on diversity such that species richness increased with resource enhancement (nutrients) and declined with disturbance. These results support the model that increased heterogeneity of distribution of limiting resources allows the coexistence of species with low and high resource requirements.

Herbivory is a key factor in regulating plant biomass, thereby driving ecosystem performance. Algae have developed multiple adaptations to cope with grazers, including morphological and chemical defences. In a series of experiments we investigated whether several species of macroalgae possess anti-herbivore defences and whether these could be regulated to demand, i.e. grazing events. The potential of direct grazing on defence induction was assessed for two brown (Dictyopteris membranacea, Fucus vesiculosus) and two red seaweeds (Gelidium sesquipedale, Sphaerococcus coronopifolius) from São Rafael and Ria Formosa, Portugal. Bioassays conducted with live algal pieces and agar-based food containing lipophilic algal extracts were used to detect changes in palatability after exposure to amphipod attacks (=treatment phase). Fucus vesiculosus was the only species significantly reducing palatability in response to direct amphipod-attacks. This pattern was observed in live F. vesiculosus pieces and agar-based food containing a lipophilic extract, suggesting that lipophilic compounds produced during the treatment phase were responsible for the repulsion of grazers. Water-borne cues of grazed F. vesiculosus as well as non-grazing amphipods also reduced palatability of neighbouring conspecifics. However, this effect was only observed in live tissues of F. vesiculosus. This study is the first to show that amphipods, like isopods, are capable to induce anti-herbivory defences in F. vesiculosus and that a seasonally variable effectiveness of chemical defences might serve as a dynamic control in alga–herbivore interactions.

Development of a mechanistic understanding and predictions of patterns of biodiversity is a central theme in ecology. One of the most influential theories, the intermediate disturbance hypothesis (IDH), predicts maximum diversity at intermediate levels of disturbance frequency. The dynamic equilibrium model (DEM), an extension of the IDH, predicts that the level of productivity determines at what frequency of disturbance maximum diversity occurs. To test, and contrast, the predictions of these two models, a field experiment on marine hard-substratum assemblages was conducted with seven levels of disturbance frequency and three levels of nutrient availability. Consistent with the IDH, maximum diversity, measured as species richness, was observed at an intermediate frequency of disturbance. Despite documented effects on productivity, the relationship between disturbance and diversity was not altered by the nutrient treatments. Thus, in this system the DEM did not improve the understanding of patterns of diversity compared to the IDH. Furthermore, it is suggested that careful consideration of measurements and practical definitions of productivity in natural assemblages is necessary for a rigorous test of the DEM.

1 Plants must either tolerate consumption or defend themselves against grazer attacks. Selection for phenotypically plastic antiherbivory responses has been suggested for many plants, including a few species of seaweed, but little is known about its specificity or seasonality. 2 Multi-factorial experiments tested the effects of consumer identity (Littorina brevicula vs. Haliotis discus) and season (summer vs. autumn) on the induction of antiherbivory defences in the brown seaweed Ecklonia cava. Following a grazer-free acclimation phase, algae were incubated with grazers (treatment phase) and, subsequently, without grazers (recovery phase). Feeding preference assays, were used to assess differences in consumption rates between grazer-exposed and control plants. 3 In summer, Littorina, but not Haliotis, induced defence in Ecklonia. This defence vanished by the end of the recovery phase. In autumn, neither exposure to direct attack nor to waterborne cues induced defensive responses. 4 Both consumer identity and season of consumption can influence the ability of a given macroalgal species to induce antiherbivory defences. Tailoring such responses to spatial and temporal variation in grazer pressure could have profound ecological implications, for example changing food webs and community structure.

Macroalgae can defend themselves against generalist and specialist herbivores via morphological and/or chemical traits. Herein we examined the defensive responses (via relative palatability) of two brown (Lessonia nigrescens, Glossophora kunthii) and two red algae (Grateloupia doryphora, Chondracanthus chamissoi) from the northern-central coast of Chile against selected generalist meso-herbivores. Two laboratory experiments were conducted to investigate whether (i) algae can respond generally to grazing pressure of meso-herbivores (amphipods, isopods and juvenile sea urchins) and whether (ii) these algal responses were inducible. In order to examine palatability and thus effectiveness of responses, feeding assays were run after each experiment using fresh algal pieces and artificial agar-based food. Lessonia nigrescens responded to amphipods but not to sea urchins, and G. kunthii showed inducible response against one species of amphipods. Grateloupia doryphora did not respond against any of the tested grazers, whereas C. chamissoi responded against one species of amphipods and the tested isopod. Our results indicate variable responses of macroalgae against selected generalist meso-herbivores and evidence of an inducible defense in the brown alga G. kunthii.

Ambient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard-bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2-3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hard-bottom communities.

Ambient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard-bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2–3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hard-bottom communities.