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Introduction: Campylobacter jejuni gastroenteritis is the most commonly reported zoonosis within the EU, with poultry products regarded as the primary source of transmission to humans. Therefore, finding strategies to reduce Campylobacter colonization in broilers holds importance for public health. Recent studies suggest that supplementation of broiler feed with brown algal extracts, particularly laminarin, can provide beneficial effects on broiler gut health, growth performance, and gut microbiota. However, its effect on gut microbiota development and subsequent reduction of Campylobacter loads in broiler caeca during the later stages of the birds' lives remains unclear. Methods: Experimental colonization of Ross 308 broilers with two different strains of C. jejuni was conducted, with groups fed either a basal diet or the same basal diet supplemented with 725 ppm algal extract from Saccharina latissima to provide 290 ppm laminarin. Fecal samples were collected for bacterial enumeration, and caecal samples were obtained before and after the C. jejuni challenge for the determination of microbiota development. Results and discussion: No significant differences in fecal C. jejuni concentrations between the groups fed different diets or exposed to different C. jejuni strains were observed. This suggests that both strains colonized the birds equally well and that the laminarin rich algal extract did not have any inhibitory effect on C. jejuni colonization. Notably, 16S rRNA amplicon sequencing revealed detailed data on the caecal microbiota development, likely influenced by both bird age and C. jejuni colonization, which can be valuable for further development of broiler feed formulations aimed at promoting gut health. [ABSTRACT FROM AUTHOR]

The green seaweed Ulva is a model system to study seaweed–bacteria interactions, but the impact of environmental drivers on the dynamics of these interactions is little understood. In this study, we investigated the stability and variability of the seaweed‐associated bacteria across the Atlantic–Baltic Sea salinity gradient. We characterized the bacterial communities of 15 Ulva sensu lato species along 2,000 km of coastline in a total of 481 samples. Our results demonstrate that the Ulva‐associated bacterial composition was strongly structured by both salinity and host species (together explaining between 34% and 91% of the variation in the abundance of the different bacterial genera). The largest shift in the bacterial consortia coincided with the horohalinicum (5–8 PSU, known as the transition zone from freshwater to marine conditions). Low‐salinity communities especially contained high relative abundances of Luteolibacter, Cyanobium, Pirellula, Lacihabitans and an uncultured Spirosomaceae, whereas high‐salinity communities were predominantly enriched in Litorimonas, Leucothrix, Sulfurovum, Algibacter and Dokdonia. We identified a small taxonomic core community (consisting of Paracoccus, Sulfitobacter and an uncultured Rhodobacteraceae), which together contributed to 14% of the reads per sample, on average. Additional core taxa followed a gradient model, as more core taxa were shared between neighbouring salinity ranges than between ranges at opposite ends of the Atlantic–Baltic Sea gradient. Our results contradict earlier statements that Ulva‐associated bacterial communities are taxonomically highly variable across individuals and largely stochastically defined. Characteristic bacterial communities associated with distinct salinity regions may therefore facilitate the host's adaptation across the environmental gradient. [ABSTRACT FROM AUTHOR]

Supergenes, tightly linked sets of alleles, offer some of the most spectacular examples of polymorphism persisting under long-term balancing selection. However, we still do not understand their evolution and persistence, especially in the face of accumulation of deleterious elements. Here, we show that an overdominant supergene in seaweed flies, Coelopa frigida, modulates male traits, potentially facilitating disassortative mating and promoting intraspecific polymorphism. Across two continents, the Cf-Inv(1) supergene strongly affected the composition of male cuticular hydrocarbons (CHCs) but only weakly affected CHC composition in females. Using gas chromatography–electroantennographic detection, we show that females can sense male CHCs and that there may be differential perception between genotypes. Combining our phenotypic results with RNA-seq data, we show that candidate genes for CHC biosynthesis primarily show differential expression for Cf-Inv(1) in males but not females. Conversely, candidate genes for odorant detection were differentially expressed in both sexes but showed high levels of divergence between supergene haplotypes. We suggest that the reduced recombination between supergene haplotypes may have led to rapid divergence in mate preferences as well as increasing linkage between male traits, and overdominant loci. Together this probably helped to maintain the polymorphism despite deleterious effects in homozygotes. [ABSTRACT FROM AUTHOR]

In the current study we investigate the antifouling potential of three polyphenolic resveratrol multimers (–)-hopeaphenol, vaticanol B and vatalbinoside A, isolated from two species of Anisoptera found in the Papua New Guinean rainforest. The compounds were evaluated against the growth and settlement of eight marine microfoulers and against the settlement and metamorphosis of Amphibalanus improvisus barnacle cyprids. The two isomeric compounds (–)-hopeaphenol and vaticanol B displayed a high inhibitory potential against the cyprid larvae metamorphosis at 2.8 and 1.1 μM. (–)-Hopeaphenol was also shown to be a strong inhibitor of both microalgal and bacterial adhesion at submicromolar concentrations with low toxicity. Resveratrol displayed a lower antifouling activity compared to the multimers and had higher off target toxicity against MCR-5 fibroblasts. This study illustrates the potential of natural products as a valuable source for the discovery of novel antifouling leads with low toxicity. [ABSTRACT FROM AUTHOR]

The Centre for Marine Evolutionary Biology (CeMEB) at the University of Gothenburg, Sweden, was established in 2008 through a 10‐year research grant of 8.7 m€ to a team of senior researchers. Today, CeMEB members have contributed >500 scientific publications, 30 PhD theses and have organised 75 meetings and courses, including 18 three‐day meetings and four conferences. What are the footprints of CeMEB, and how will the centre continue to play a national and international role as an important node of marine evolutionary research? In this perspective article, we first look back over the 10 years of CeMEB activities and briefly survey some of the many achievements of CeMEB. We furthermore compare the initial goals, as formulated in the grant application, with what has been achieved, and discuss challenges and milestones along the way. Finally, we bring forward some general lessons that can be learnt from a research funding of this type, and we also look ahead, discussing how CeMEB's achievements and lessons can be used as a springboard to the future of marine evolutionary biology. [ABSTRACT FROM AUTHOR]

The sponge derived 2,5-diketopiperazine metabolite barettin is a potent antifouling compound effective against the settlement and metamorphosis of barnacles. Simplified derivatives of barettin have previously been shown to display similar inhibitory properties. The synthetic derivative benzo[g]dipodazine has been reported to display significantly improved antifouling properties in comparison with the native barettin with inhibitory activities as low a 0.034 µM reported against barnacle cyprid settlement. In the current study we report the antifouling activity of 29 synthetic analogs designed and inspired by the potent antifouling effect seen for benzo[g]dipodazine. The library contains mainly not only dipodazine derivatives but also disubstituted diketopiperazines and compounds incorporating alternative heterocyclic cores such as hydantoin, creatinine, and rhodanine. Several of the prepared compounds inhibit the settlement of Amphibalanus improvisus cyprids at low micromolar concentrations, in parity with the natural barettin. While several highly active compounds were prepared by incorporating the benzo[g]indole as hydrophobic substituent, the remarkable antifouling effect reported for benzo[g]dipodazine was not observed when evaluated in our study. [ABSTRACT FROM AUTHOR]

Inversions often underlie complex adaptive traits, but the genic targets inside them are largely unknown. Gene expression profiling provides a powerful way to link inversions with their phenotypic consequences. We examined the effects of the Cf‐Inv(1) inversion in the seaweed fly Coelopa frigida on gene expression variation across sexes and life stages. Our analyses revealed that Cf‐Inv(1) shapes global expression patterns, most likely via linked variation, but the extent of this effect is variable, with much stronger effects in adults than larvae. Furthermore, within adults, both common as well as sex‐specific patterns were found. The vast majority of these differentially expressed genes mapped to Cf‐Inv(1). However, genes that were differentially expressed in a single context (i.e., in males, females, or larvae) were more likely to be located outside of Cf‐Inv(1). By combining our findings with genomic scans for environmentally associated SNPs, we were able to pinpoint candidate variants in the inversion that may underlie mechanistic pathways that determine phenotypes. Together the results of this study, combined with previous findings, support the notion that the polymorphic Cf‐Inv(1) inversion in this species is a major factor shaping both coding and regulatory variation resulting in highly complex adaptive effects. [ABSTRACT FROM AUTHOR]

Biofouling by opportunistic epiphytes is a major concern in seaweed aquaculture. Colonisation of fouling organisms contributes to a reduction in algal performance as well as a lower quality crop. Further, epiphyte removal techniques often increase maintenance costs of cultivation systems. There have been a variety of methods to mitigate fouling in tank cultivations of seaweed, including the use of biological controls. Here, we present the use of filter feeding bivalves, the blue mussel (Mytilus edulis) and Pacific oyster (Magallana gigas), as a novel biofilter that also serves as a source of dissolved inorganic nitrogen in tank cultivations of the sugar kelp, Saccharina latissima. We observed significant reductions of fouling epiphytes on seaweed blades of around 50% by bivalve filtration, significant elevations of ammonium (NH4+) and phosphate (PO43−) by bivalves and alterations to kelp tissue quality when co-cultivated with bivalves rather than supplied with ambient seawater. Stable isotope ratios and seawater chlorophyll a concentrations provided evidence for bivalve biofiltration and the incorporation of their by-products into kelp tissue. [ABSTRACT FROM AUTHOR]

Ocean acidification driven by anthropogenic climate change is causing a global decrease in pH, which is projected to be 0.4 units lower in coastal shallow waters by the year 2100. Previous studies have shown that seaweeds grown under such conditions may alter their growth and photosynthetic capacity. It is not clear how such alterations might impact interactions between seaweed and herbivores, e.g. through changes in feeding rates, nutritional value, or defense levels. Changes in seaweeds are particularly important for coastal food webs, as they are key primary producers and often habitat-forming species. We cultured the habitat-forming brown seaweed Fucus vesiculosus for 30 days in projected future pCO2 (1100 μatm) with genetically identical controls in ambient pCO2 (400 μatm). Thereafter the macroalgae were exposed to grazing by Littorina littorea, acclimated to the relevant pCO2-treatment. We found increased growth (measured as surface area increase), decreased tissue strength in a tensile strength test, and decreased chemical defense (phlorotannins) levels in seaweeds exposed to high pCO2-levels. The herbivores exposed to elevated pCO2-levels showed improved condition index, decreased consumption, but no significant change in feeding preference. Fucoid seaweeds such as F. vesiculosus play important ecological roles in coastal habitats and are often foundation species, with a key role for ecosystem structure and function. The change in surface area and associated decrease in breaking force, as demonstrated by our results, indicate that F. vesiculosus grown under elevated levels of pCO2 may acquire an altered morphology and reduced tissue strength. This, together with increased wave energy in coastal ecosystems due to climate change, could have detrimental effects by reducing both habitat and food availability for herbivores. [ABSTRACT FROM AUTHOR]

Seaweed aquaculture is receiving increasing attention for food and non-food applications in Europe, where it is still an emerging industry. The cultivation of seaweeds in the sea is attractive as it does not compete with agricultural crops for land and freshwater, whilst generating high yearly biomass yield. The selection of suitable cultivation sites in coastal waters is essential for the sustainable establishment and further development of seaweed aquaculture in Europe. Here, we investigate the effects of wave exposure and geographic location on growth and biofouling of kelp (Saccharina latissima), using a transplantation experiment along the Swedish west coast. Biofouling of kelp decreased with increased wave exposure, from 10 and 6% coverage at sheltered and moderately exposed locations, respectively, to 3% at exposed locations. Growth, measured as blade surface area, generally increased with decreased wave exposure, with approximately 40% less growth at exposed locations compared to sheltered or moderately exposed location. We identified that there is large spatial variation in growth and fouling of the seaweed biomass at the selected farm sites, with significant differences from the km-scale to the m-scale. In addition, exposure level affected the tissue composition, with a high carbon, but low nitrogen and water content at exposed locations compared to moderate and sheltered sites. Isotope signatures (i.e. δ13C and δ15N) also differed between exposure levels. Together, these results indicate that wave exposure is an important factor to consider in site selection for both yield as well as quality of the seaweed biomass for future kelp farms. [ABSTRACT FROM AUTHOR]

Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition). [ABSTRACT FROM AUTHOR]

In recent years, the interest in using seaweed for the sustainable production of commodities has been increasing as seaweeds contain many potentially worthwhile compounds. Thus, the extraction and refining processes of interesting compounds from seaweeds is a hot research topic but has been found to have problems with profitability for novel applications. To increase the economic potential of refining seaweed biomass, the content of the compounds of interest should be maximized, which can potentially be achieved through optimization of cultivation conditions. In this study, we studied how the monosaccharide composition of the green seaweed species Ulva fenestrata is influenced by the abiotic factors; irradiance, temperature, nitrate, phosphate, and pCO2. It was evident that lower nitrate concentration and cultivation at elevated temperature increased monosaccharide contents. A 70% increase in iduronic acid and a 26% increase in rhamnose content were seen under elevated irradiance and temperature conditions, though the absolute differences in monosaccharide concentration were small. Irradiance and nitrate impacted the ratio between iduronic and rhamnose, which is an indicator of the ulvan structure. These results could potentially be utilized to coax the ulvan towards specific bioactivities, and thus have a considerable impact on a potential biorefinery centered around Ulva. [ABSTRACT FROM AUTHOR]

We report (1) successful extraction and characterization of cellulose from northern hemisphere green macroalgae Ulva lactuca (Ulva fenestrata) collected along the Swedish west coast and cultivated indoors under controlled conditions, followed by (2) its utilization in the production of lignin-free cellulose nanofibrils (CNF). Cellulose was extracted by sequential treatment with ethanol, hydrogen peroxide, sodium hydroxide, and hydrochloric acid, yielding a cellulose-rich insoluble fraction. The extracted cellulose was disintegrated into CNF using a mechanical homogenization process without any further enzymatic pre-treatments. In addition, regenerated cellulose was prepared. XRD characterization of the CNF showed characteristic peaks for the cellulose I allomorph and confirmed that the nanofibrils were semicrystalline with a crystallinity index of 48%. Regenerated cellulose was mostly amorphous with an XRD pattern indicating the presence of the cellulose II allomorph. The cellulose fractions were essentially free from inorganic substances and thermally stable up to around 260 °C. Structural mapping with CP-MAS 13C-NMR sustains the cellulose content of CNF and regenerated cellulose, respectively, yet ion chromatography identified the presence of 10–15% xylose in the fractions. Optotracing was used as a novel and non-disruptive tool to selectively assess the polysaccharide composition of the cellulose fractions and produced CNF aiming to shed light on this hitherto non-resolved origin of xylose in Ulva cell wall matter. Fluorescence excitation and emission spectra of a panel of 4 oligothiophenes identified and verified the presence of cellulose and sustain the conclusion that the isolated fractions consist of cellulose intertwined with a small amount of a xylose-containing glucan copolymer. [ABSTRACT FROM AUTHOR]

Seaweed cultivation is a large industry worldwide, but production in Europe is small compared to production in Asian countries. In the EU, the motivations for seaweed farming may be seen from two perspectives; one being economic growth through biomass production and the other being the provisioning of ecosystem services such as mitigating eutrophication. In this paper, we assess the economic potential of large-scale cultivation of kelp, Saccharina latissima, along the Swedish west coast, including the value of externalities. The findings suggest that seaweed farming has the potential of becoming a profitable industry in Sweden. Furthermore, large-scale seaweed farming can sequester a significant share of annual anthropogenic nitrogen and phosphorus inflows to the basins of the Swedish west coast (8% of N and 60% of P). Concerning the valuation of externalities, positive values generated from sequestration of nitrogen and phosphorus are potentially counteracted by negative values from interference with recreational values. Despite the large N and P uptake, the socioeconomic value of this sequestration is only a minor share of the potential financial value from biomass production. This suggests that e.g. payment schemes for nutrient uptake based on the socioeconomic values generated is not likely to be a tipping point for the industry. Additionally, seaweed cultivation is not a cost-efficient measure in itself to remove nutrients. Policy should thus be oriented towards industry development, as the market potential of the biomass will be the driver that may unlock these bioremediation opportunities. [ABSTRACT FROM AUTHOR]

Cuticular hydrocarbons (CHCs) form the boundary between insects and their environments and often act as essential cues for species, mate, and kin recognition. This complex polygenic trait can be highly variable both among and within species, but the causes of this variation, especially the genetic basis, are largely unknown. In this study, we investigated phenotypic and genetic variation of CHCs in the seaweed fly, Coelopa frigida, and found that composition was affected by both genetic (sex and population) and environmental (larval diet) factors. We subsequently conducted behavioral trials that show CHCs are likely used as a sexual signal. We identified general shifts in CHC chemistry as well as individual compounds and found that the methylated compounds, mean chain length, proportion of alkenes, and normalized total CHCs differed between sexes and populations. We combined these data with whole genome resequencing data to examine the genetic underpinnings of these differences. We identified 11 genes related to CHC synthesis and found population‐level outlier SNPs in 5 that are concordant with phenotypic differences. Together these results reveal that the CHC composition of C. frigida is dynamic, strongly affected by the larval environment, and likely under natural and sexual selection. [ABSTRACT FROM AUTHOR]

In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co‐occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard‐bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply. [ABSTRACT FROM AUTHOR]

A range of natural products from marine invertebrates, bacteria and fungi have been assessed as leads for nature-inspired antifouling (AF) biocides, but little attention has been paid to microalgal-derived compounds. This study assessed the AF activity of the spirocyclic imine portimine (1), which is produced by the benthic mat-forming dinoflagellate Vulcanodinium rugosum. Portimine displayed potent AF activity in a panel of four macrofouling bioassays (EC50 0.06-62.5 ng ml−1), and this activity was distinct from that of the related compounds gymnodimine-A (2), 13-desmethyl spirolide C (3), and pinnatoxin-F (4). The proposed mechanism of action for portimine is induction of apoptosis, based on the observation that portimine inhibited macrofouling organisms at developmental stages known to involve apoptotic processes. Semisynthetic modification of select portions of the portimine molecule was subsequently undertaken. Observed changes in bioactivity of the resulting semisynthetic analogues of portimine were consistent with portimine's unprecedented 5-membered imine ring structure playing a central role in its AF activity. [ABSTRACT FROM AUTHOR]

By combining the recently reported repelling natural dihydrostilbene scaffold with an oxime moiety found in many marine antifoulants, a library of nine antifouling hybrid compounds was developed and biologically evaluated. The prepared compounds were shown to display a low antifouling effect against marine bacteria but a high potency against the attachment and growth of microalgae down to MIC values of 0.01 μg/mL for the most potent hybrid. The mode of action can be characterized as repelling via a reversible non-toxic biostatic mechanism. Barnacle cyprid larval settlement was also inhibited at low μg/mL concentrations with low levels or no toxicity observed. Several of the prepared compounds performed better than many reported antifouling marine natural products. While several of the prepared compounds are highly active as antifoulants, no apparent synergy is observed by incorporating the oxime functionality into the dihydrostilbene scaffold. This observation is discussed in light of recently reported literature data on related marine natural antifoulants and antifouling hybrids as a potentially general strategy for generation of improved antifoulants. [ABSTRACT FROM AUTHOR]

Non-native seaweeds constitute a conspicuous component of many benthic coastal communities. Seaweed invaders are known to significantly affect invaded communities, but relatively little is known about the mechanisms underlying their success. In this study, we explored the feeding preferences of three generalist herbivores for the successful non-native red alga Heterosiphonia japonica and native seaweed competitors. The experiments were conducted on the Swedish Skagerrak coast (58°52′N, 11°08′E) from July to August. Additionally, chemical and physical traits of the seaweeds were assessed to mechanistically explain herbivore preferences. The results showed that H. japonica was of low preference to native herbivores and that this was most likely explained by chemical properties of the invader. We were, however, not able to determine whether the low preference was caused by deterrent metabolites or low nutritional quality. We conclude that herbivore avoidance may be important for the survival and success of H. japonica in the introduced range and that efficient means of escaping herbivory may be a common feature of invaders in seaweed communities. [ABSTRACT FROM AUTHOR]

This study monitored the biomass composition of Saccharina latissima during a potential harvesting season on the West coast of Sweden, in order to find suitable harvest times for biorefinery purposes. Specimens of S. latissima were sampled at three locations in June, August and October and the biomass was analysed for its macromolecular composition, as well as for the content of several specific compounds, e.g. sugars and fatty acids. PERMANOVA analyses showed that there was a significant difference in the biomass composition among time points. The total carbohydrate concentration was lowest in June and peaked at 360 mg g-1 dry weight in August, while the mannitol content was highest, 90 mg g-1, in June and decreased throughout the sampling period. Total protein and fatty acid concentrations were found to be approximately 80 and 3 mg g-1, respectively, with relatively little variation over time. Overall, there was little spatial variation in the macromolecular composition, although the concentration of some specific monosaccharides and fatty acids, as well as the total phenolic content, differed among localities. We discuss the implications of the observed variation in biomass composition of S. latissima for future biorefinery purposes. [ABSTRACT FROM AUTHOR]

The allocation of resources to different life-history traits should represent the best compromise in fitness investment for organisms in their local environment. When resources are limiting, the investment in a specific trait must carry a cost that is expressed in trade-offs with other traits. In this study, the relative investment in the fitness-related traits, growth, reproduction and defence were compared at central and range-edge locations, using the seaweed Ascophyllum nodosum as a model system. Individual growth rates were similar at both sites, whereas edge populations showed a higher relative investment in reproduction (demonstrated by a higher reproductive allocation and extended reproductive periods) when compared to central populations that invested more in defence. These results show the capability of A. nodosum to differentially allocate resources for different traits under different habitat conditions, suggesting that reproduction and defence have different fitness values under the specific living conditions experienced at edge and central locations. However, ongoing climate change may threaten edge populations by increasing the selective pressure on specific traits, forcing these populations to lower the investment in other traits that are also potentially important for population fitness. [ABSTRACT FROM AUTHOR]

Interactions among microscopic planktonic organisms underpin the functioning of open ocean ecosystems. With few exceptions, these organisms lack advanced eyes and thus rely largely on chemical sensing to perceive their surroundings. However, few of the signaling molecules involved in interactions among marine plankton have been identified. We report a group of eight small molecules released by copepods, the most abundant zooplankton in the sea, which play a central role in food webs and biogeochemical cycles. The compounds, named copepodamides, are polar lipids connecting taurine via an amide to isoprenoid fatty acid conjugate of varying composition. The bloom-forming dinoflagellate Alexandrium minutum responds to pico- to nanomolar concentrations of copepodamides with up to a 20-fold increase in production of paralytic shellfish toxins. Different copepod species exude distinct copepodamide blends that contribute to the species- specific defensive responses observed in phytoplankton. The signaling system described here has far reaching implications for marine ecosystems by redirecting grazing pressure and facilitating the formation of large scale harmful algal blooms. [ABSTRACT FROM AUTHOR]

A series of 13 short synthetic amphiphilic cationic micropeptides, derived from the antimicrobial iron-binding innate defence protein lactoferrin, have been evaluated for their capacity to inhibit the marine fouling process. The whole biofouling process was studied and microfouling organisms such as marine bacteria and microalgae were included as well as the macrofouling barnacleBalanus improvisus. In total 19 different marine fouling organisms (18 microfoulers and one macrofouler) were included and both the adhesion and growth of the microfoulers were investigated. It was shown that the majority of the peptides inhibited barnacle cyprid settlementviaa reversible nontoxic mechanism, with IC50values as low as 0.5 μg ml−1. Six peptides inhibited adhesion and growth of microorganisms. Two of these were particularly active against the microfoulers with MIC-values ranging between 0.01 and 1 μg ml−1, which is comparable with the commercial reference antifoulant SeaNine. [ABSTRACT FROM AUTHOR]

Photosynthesis is a fundamental process sustaining heterotrophic organisms at all trophic levels. Some mixotrophs can retain functional chloroplasts from food (kleptoplasty), and it is hypothesized that carbon acquired through kleptoplasty may enhance trophic energy transfer through increased host growth efficiency. Sacoglossan sea slugs are the only known metazoans capable of kleptoplasty, but the relative fitness contributions of heterotrophy through grazing, and phototrophy via kleptoplasts, are not well understood. Fitness benefits (i.e. increased survival or growth) of kleptoplasty in sacoglossans are commonly studied in ecologically unrealistic conditions under extended periods of complete darkness and/or starvation. We compared the growth efficiency of the sacoglossan Elysia viridis with access to algal diets providing kleptoplasts of differing functionality under ecologically relevant light conditions. Individuals fed Codium fragile, which provide highly functional kleptoplasts, nearly doubled their growth efficiency under high compared to low light. In contrast, individuals fed Cladophora rupestris, which provided kleptoplasts of limited functionality, showed no difference in growth efficiency between light treatments. Slugs feeding on Codium, but not on Cladophora, showed higher relative electron transport rates (rETR) in high compared to low light. Furthermore, there were no differences in the consumption rates of the slugs between different light treatments, and only small differences in nutritional traits of algal diets, indicating that the increased growth efficiency of E. viridis feeding on Codium was due to retention of functional kleptoplasts. Our results show that functional kleptoplasts from Codium can provide sacoglossan sea slugs with fitness advantages through photosynthesis. [ABSTRACT FROM AUTHOR]

The inhibition of marine biofouling by the bromotyrosine derivative ianthelline, isolated from the Arctic marine sponge Stryphnus fortis, is described. All major stages of the fouling process are investigated. The effect of ianthelline on adhesion and growth of marine bacteria and microalgae is tested to investigate its influence on the initial microfouling process comparing with the known marine antifoulant barettin as a reference. Macrofouling is studied via barnacle ( Balanus improvisus) settlement assays and blue mussel ( Mytilus edulis) phenoloxidase inhibition. Ianthelline is shown to inhibit both marine micro- and macrofoulers with a pronounced effect on marine bacteria (minimum inhibitory concentration (MIC) values 0.1-10 μg/mL) and barnacle larval settlement (IC = 3.0 μg/mL). Moderate effects are recorded on M. edulis (IC = 45.2 μg/mL) and microalgae, where growth is more affected than surface adhesion. The effect of ianthelline is also investigated against human pathogenic bacteria. Ianthelline displayed low micromolar MIC values against several bacterial strains, both Gram positive and Gram negative, down to 2.5 μg/mL. In summary, the effect of ianthelline on 20 different representative marine antifouling organisms and seven human pathogenic bacterial strains is presented. [ABSTRACT FROM AUTHOR]

Factors determining the degree of dietary generalism versus specialism are central in ecology. Species that are generalists at the population level may in fact be composed of specialized individuals. The optimal diet theory assumes that individuals choose diets that maximize fitness, and individual specialization may occur if individuals' ability to locate, recognize, and handle different food types differ. We investigate if individuals of the marine herbivorous slug Elysia viridis, which co-occur at different densities on several green macroalgal species in the field, are specialized to different algal hosts. Individual slugs were collected from three original algal host species (Cladophora sericea, Cladophora rupestris and Codium fragile) in the field, and short-term habitat choice and consumption, as well as long-term growth (proxy for fitness), on four algal diet species (the original algal host species and Chaetomorpha melagonium) were studied in laboratory experiments. Nutritional (protein, nitrogen, and carbon content) and morphological (dry weight, and cell/utricle volume) algal traits were also measured to investigate if they correlated with the growth value of the different algal diets. E. viridis individuals tended to choose and consume algal species that were similar to their original algal host. Long-term growth of E. viridis, however, was mostly independent of original algal host, as all individuals reached a larger size on the non-host C. melagonium. E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits. Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles. We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT. [ABSTRACT FROM AUTHOR]

The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits. [ABSTRACT FROM AUTHOR]

• Early feed access and use of algal extract in chicken starter diets were explored. • Growth rate, feed intake and bursa development were improved by early feed access. • No effects of early feed access on gut microbiota or antibody response was detected. • Algal extract supplementation did not affect growth performance or gut health. • Early feed access may be used to improve growth performance in broiler chickens. Hatching concepts such as on-farm hatching provide an opportunity to supply newly hatched chickens with optimal nutrition that support growth and development of a healthy gut. Brown algae contain bioactive compounds, especially laminarin and fucoidan that may improve intestinal health and immune responses. This study aimed to examine the effects of early access to feed and water posthatch and feed supplementation with algal extract rich in laminarin from Laminaria digitata, on growth performance, organ and microbiota development and antibody production. A total of 432 Ross 308 chicks were allotted to 36 rearing pens in a 2 × 3 factorial design with two hatching treatments and three dietary treatments. During chick placement, half of the pens were directly provided access to feed and water (Early) while half of the pens were deprived of feed and water for 38 h (Late). The chicks were fed three different starter diets until day 6; a wheat-soybean meal-based control diet, a diet with low inclusion of algal extract (0.057%) and a diet with high inclusion of algal extract (0.114%). Feed intake and BW were registered on pen basis at placement, days 1, 6, 12, 19, 26, 33 and 40. To induce antibody responses, all chicks were vaccinated against avian pneumovirus on day 10. Three chicks per pen were selected as focal animals and used for blood sampling on days 10 and 39. On days 6, 19, and 40, two birds per pen were killed and used for organ measurement and caecal digesta sampling for gut microbiota analysis using the Illumina Miseq PE 250 sequencing platform. Results showed that algal extract did not influence gut microbiota, gut development or vaccine-induced antibody responses. However, during the first 38 h, early-fed chicks consumed on average 19.6 g of feed and gained 27% in BW, while late-fed chicks lost 9.1% in BW which lowered BW and feed intake throughout the study (P < 0.05). Late chicks also had longer relative intestine, higher relative (g/kg BW) weight of gizzard and proventriculus but lower relative bursa weight on day 6 (P < 0.05). No effects of hatching treatment on microbiota or antibody response were detected. The microbiota was affected by age, where alpha diversity increased with age. In conclusion, this study showed that early access to feed but not algal extract improved the growth performance throughout the 40-day growing period, and stimulated early bursa development. [ABSTRACT FROM AUTHOR]

A number of studies have shown that the production of chemical defences is costly in terrestrial vascular plants. However, these studies do not necessarily reflect the costs of defence production in macroalgae, due to structural and functional differences between vascular plants and macroalgae. Using a specific culturing technique, we experimentally manipulated the defence production in the red alga Bonnemaisonia hamifera to examine if the defence is costly in terms of growth. Furthermore, we tested if the defence provides fitness benefits by reducing harmful bacterial colonisation of the alga. Costly defences should provide benefits to the producer in order to be maintained in natural populations, but such benefits through protection against harmful bacterial colonisation have rarely been documented in macroalgae. We found that algae with experimentally impaired defence production, but with an externally controlled epibacterial load, grew significantly better than algae with normal defence production. We also found that undefended algae exposed to a natural epibacterial load experienced a substantial reduction in growth and a 6-fold increase in cell bleaching, compared to controls. Thus, this study provides experimental evidence that chemical defence production in macroalgae is costly, but that the cost is outweighed by fitness benefits provided through protection against harmful bacterial colonisation. [ABSTRACT FROM AUTHOR]

Allelopathy is an important non-resource interaction in terrestrial plant communities that may affect invasions by non-indigenous plants. The 'novel weapons hypothesis' ( NWH) predicts that non-indigenous plants will become invasive if they have allelopathic compounds that assemblages in the new range are not adapted to. Recently, the non-indigenous, chemically rich macroalga Bonnemaisonia hamifera (Hariot) has become one of the most abundant filamentous red algae in Scandinavian waters., We used B. hamifera to specifically test the aspect of the NWH that concerns invasion success based on novel allelochemicals in the invaded range. Allelopathic interactions were tested through effects on the growth rate of adult native macroalgae in co-cultures with B. hamifera and through the settlement success of native macroalgal propagules and microalgae on surfaces coated with 1,1,3,3-tetrabromo-2-heptanone. We also investigated whether 1,1,3,3-tetrabromo-2-heptanone can be transferred from B. hamifera to its native host algae, as a means of pre-emptive competition., The settlement of native macroalgal propagules and microalgae was strongly inhibited on surfaces coated with 1,1,3,3-tetrabromo-2-heptanone at ecologically relevant concentrations, but there were no effects of adult B. hamifera on growth rates of adults of the six native naturally co-occurring species. The compound was shown to be transferred from B. hamifera to the surface of its native host algae at inhibitory concentrations in both laboratory and field experiments., By inhibiting the settlement of propagules on its thallus and on surrounding surfaces, B. hamifera achieves a competitive advantage over native macroalgae, a finding that parallels previous reports on soil- and litter-mediated allelopathic interactions among vascular plants. Because competition for available substrata in marine benthic systems is intense, the ability to reserve space may be vital for B. hamifera's successful invasion. This is the first example of an allelopathic compound that can be transferred by direct contact from an exotic to a native species, with an active and unaltered function., Synthesis. Our results clearly show that the main secondary metabolite of the invasive red alga B. hamifera has strong allelopathic effects towards native competitors, suggesting that its novel chemical weapon is important for the highly successful invasion of new ranges. [ABSTRACT FROM AUTHOR]

Invasion success of introduced species is often attributed to a lack of natural enemies as stated by the enemy release hypothesis (ERH). The ERH intuitively makes sense for specialized enemies, but it is less evident why invaders in their new area escape attacks by generalist enemies. A recent hypothesis explains low herbivore damage on invasive plants with plant defense chemicals that are evolutionarily novel to native herbivores. Support for this novel weapon hypothesis (NWH) is so far based on circumstantial evidence. To corroborate the NWH, there is a need for direct evidence through explicit characterizations of the novel chemicals and their effects on native consumers. This study evaluated the NWH using the highly invasive red alga Bonnemaisortia hamifera. In pairwise feeding experiments, preferences between B. hamifera and native competitors were assessed for four common generalist herbivores in the invaded area. Through a bioassay-guided fractionation, we identified the deterrent compound and verified its effect in an experiment with the synthesized compound at natural concentrations. The results showed that native herbivores strongly preferred native algae to B. hamifera. The resistance against herbivores could be tracked down to the algal metabolite 1,1,3,3-tetrabromo-2-heptanone, a compound not known from native algae in the invaded area. The importance of the chemical defense was further underlined by the feeding preference of herbivores for individuals with a depleted content of l,l,3,3-tetrabromo-2-heptanone. This study thus provides the first conclusive example of a highly successful invader where low consumption in the new range can be directly attributed to a specific chemical defense against evolutionarily naïve native generalists. In conclusion, our results support the notion that novel chemical weapons against naïve herbivores can provide a mechanistic explanation for plant invasion success. [ABSTRACT FROM AUTHOR]

Bacteria associated with seaweeds can both harm and benefit their hosts. Many seaweed species are known to produce compounds that inhibit growth of bacterial isolates, but the ecological role of seaweed metabolites for the associated bacterial community structure is not well understood. In this study the response of a colonizing bacterial community to the secondary metabolite (1,1,3,3-tetrabromo-2-heptanone) from the red alga Bonnemaisonia hamifera was investigated by using field panels coated with the metabolite at a range of concentrations covering those measured at the algal surface. The seaweed metabolite has previously been shown to have antibacterial effects. The metabolite significantly affected the natural fouling community by (i) altering the composition, (ii) altering the diversity by increasing the evenness and (iii) decreasing the density, as measured by terminal restriction fragment length polymorphism in conjunction with clone libraries of the 16S rRNA genes and by bacterial enumeration. No single major bacterial taxon (phylum, class) was particularly affected by the metabolite. Instead changes in community composition were observed at a more detailed phylogenetic level. This indicates a broad specificity of the seaweed metabolite against bacterial colonization, which is supported by the observation that the bacterial density was significantly affected at a lower concentration (0.02 μg cm−2) than the composition (1–2.5 μg cm−2) and the evenness (5 μg cm−2) of the bacterial communities. Altogether, the results emphasize the role of secondary metabolites for control of the density and structure of seaweed-associated bacterial communities. [ABSTRACT FROM PUBLISHER]

Non-indigenous species (NIS) are important components of global change, and in order to manage such species it is important to understand which factors affect their success. Interactions with enemies in the new range have been shown to be important for the outcome of introductions, but thus far most studies on NIS-enemy interactions have considered only specialist herbivores in terrestrial systems. Here we present the results from the first biogeographic study that compares herbivore resistance between populations in the native and new region of a non-indigenous seaweed. We show that low consumption of the non-indigenous seaweed by a generalist herbivore is caused by higher chemical defence levels and herbivore resistance in the new range-and not by the failure of the herbivore to recognise the non-indigenous seaweed as a suitable host. Since most seaweed-herbivore interactions are dominated by generalist herbivores, this pattern could be common in marine communities. Our results also reveal that traits used to predict the invasive potential of species, such as their resistance to enemies, can change during the invasion process, but not always in the way predicted by dominant theories. [ABSTRACT FROM AUTHOR]

Physical and biological disturbances are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively, depending on levels of productivity (e.g., the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard-substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity was manipulated as high or ambient. Uni- and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and total species richness. Algal richness was significantly affected by productivity and biological disturbance, whereas invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbances affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e., press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities, and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment. [ABSTRACT FROM AUTHOR]

Ecological research on algal-derived metabolites with antimicrobial activity has recently received increased attention and is no longer only aimed at identifying novel natural compounds with potential use in applied perspectives. Despite this progress, few studies have so far demonstrated ecologically relevant antimicrobial roles of algal metabolites, and even fewer have utilized molecular tools to investigate the effects of these metabolites on the natural community composition of bacteria. In this study, we investigated whether the red alga Bonnemaisonia asparagoides is chemically defended against bacterial colonization of its surface by extracting surface-associated secondary metabolites and testing their antibacterial effects. Furthermore, we compared the associated bacterial abundance and community composition between B. asparagoides and two coexisting macroalgae. Surface extracts tested at natural concentrations had broad-spectrum effects on the growth of ecologically relevant bacteria, and consistent with this antibacterial activity, natural populations of B. asparagoides had significantly lower densities of epibacteria compared with the coexisting algae. Terminal restriction fragment length polymorphism analysis further showed that B. asparagoides harboured surface-associated bacteria with a community composition that was significantly different from those on coexisting macroalgae. Altogether, these findings demonstrate that B. asparagoides produces surface-bound antibacterial compounds with a significant impact on the abundance and composition of the associated bacterial community. [ABSTRACT FROM AUTHOR]

Many planktonic microalgae produce a range of toxins and may form harmful algal blooms. One hypothesis is that some toxins are allelopathic. suppressing the growth of competitors, and it has been suggested that allelopathy may be one important mechanism causing algal blooms. In a metaanalysis of recent experimental work, we looked for evidence that allelopathy may explain the initiation of algal blooms. With few exceptions, allelopathic effects were only significant at very high cell densities typical of blooms. We conclude that there is no experimental support for allelopathy at prebloom densities, throwing doubts on allelopathy as a mechanism in bloom formation. Most studies tested allelopathy using cell-free manipulations. With simple models we show that cell-free manipulations may underestimate allelopathy at low cell densities if effects are transmitted during cell-cell interactions. However, we suggest that the evolution of allelopathy under field conditions may be unlikely even if based on cell-cell interactions. The spatial dispersion of cells in turbulent flow will make it difficult for an allelopathic cell to receive an exclusive benefit, and a dispersion model shows that dividing cells are rapidly separated constraining clone selection. Instead, we propose that reported allelopathic effects may be nonadaptive side effects of predator-prey or casual parasitic cell-cell interactions. [ABSTRACT FROM AUTHOR]

Understanding the demography and function of biotope-forming seaweed species is of great importance for the conservation of the target species itself, as well as its associated organisms. The brown seaweed Ascophyllum nodosum is fundamental for the functioning of coastal marine ecosystems in the North Atlantic. In this study, we use a data-based size-classified matrix model to investigate the temporal and spatial variability in demography, and the environment-specific stochastic sensitivity and elasticity, of two A. nodosum populations, one in western Sweden and one on the Isle of Man in the Irish Sea. A significant difference between the two populations was that the Swedish population had comparably low and more variable stochastic population growth rate ( λs). This pattern was partly explained by the relatively high and varying mortality rates during extreme ice-years in Sweden, and by the lower survival of small individuals during all years. There were also fewer large individuals in Sweden due to lower transitions to the larger size-classes and higher probability of shrinkage. Sensitivities were analogous in the two populations, and showed a high selection pressure for increased individual growth. Elasticities were also similar, with the exception that survival of the smallest individuals (i.e., transition a1,1), had a higher elasticity on the Isle of Man. Overall, the stochastic growth rate ( λs) was most sensitive to proportional changes in loop- (i.e., survival within size-class) and, to some extent, growth-transitions in both study areas. These results show that structurally and demographically diverging A. nodosum populations may be similarly sensitive to changes in vital rates. This, in turn, indicates a plastic life history of A. nodosum that may cope with large environmental variability. The results further suggest that environmental change affecting the survival or growth of the larger, reproductive A. nodosum individuals could have severe and regional effects on the abundance and biomass of this species, with potential negative effects on the biodiversity of the associated communities. [ABSTRACT FROM AUTHOR]

Empirical evidence suggests that disturbance has profound effects on the species diversity of aquatic and terrestrial assemblages. Conceptual ecological theories, such as the intermediate disturbance hypothesis (IDH), predict maximum diversity at intermediate levels of disturbance. Tests of the predictive power and generality of these models are, however, hampered by the fact that the meaning and units of "disturbance" are not clearly defined. For example, it is seldom recognized that the rate of disturbance is the product of both frequency and extent (e.g., area or volume) of disturbance events. This has important consequences for the design and interpretation of experiments on disturbance. Here we present,, for the first time, an experimental design that allows for unconfounded testing of combinations of area and frequency (i.e., regimes) for a given rate of disturbance. We tested the prediction that species richness responds differently to equal rates of disturbance, depending on the specific combination of frequency and area, on marine hard-substratum assemblages. Five different rates of disturbance and two regimes (small frequent or large infrequent disturbances) were applied at three sites. The results showed that the effect of a certain rate of disturbance (1) varies strongly among assemblages and (2) also depends on the specific combination of frequency and area of disturbance events. Maximum species richness was observed at intermediate rates of disturbance at site 1 (i.e., support for the IDH), whereas there was a monotonic decline at site 2 and there was no evident pattern at site 3. The variable responses among sites were explained by differences in degree of competitive exclusion and rates of recruitment. At the site where the IDH was supported, the regime with a large proportion of the area disturbed infrequently showed higher richness, compared to the regime with a small proportion disturbed frequently. This was likely due to a stronger decrease of dominants, which allowed for the recruitment of new colonizing species. In summary, we conclude that tests and general syntheses of models of disturbance-diversity patterns would benefit from more explicit definitions of the components of disturbance, as well as a stronger focus on the importance of variation in inherent properties of natural assemblages. [ABSTRACT FROM AUTHOR]

The dinoflagellate Alexandrium minutum has previously been shown to produce paralytic shellfish toxins (PST) in response to waterborne cues from the copepod Acartia tonsa. In order to investigate if grazer-induced toxin production is a general or grazer-specific response of A. minutum to calanoid copepods, we exposed two strains of A. minutum to waterborne cues from three other species of calanoid copepods, Acartia clausi, Centropages typicus and Pseudocalanus sp. Both A. minutum strains responded to waterborne cues from Centropages and Acartia with significantly increased cell-specific toxicity. Waterborne cues from Centropages caused the strongest response in the A. minutum cells, with 5 to >20 times higher toxin concentrations compared to controls. In contrast, neither of the A. minutum strains responded with significantly increased toxicity to waterborne cues from Pseudocalanus. The absolute increase in PST content was proportional to the intrinsic toxicity of the different A. minutum strains that were used. The results show that grazer-induced PST production is a grazer-specific response in A. minutum, and its potential ecological importance will thus depend on the composition of the zooplankton community, as well as the intrinsic toxin-producing properties of the A. minutum population. [ABSTRACT FROM AUTHOR]

Plants have different strategies to cope with herbivory, including induction of chemical defences and compensatory growth. The most favourable strategy for an individual plant may depend on the density at which the plants are growing and on the availability of nutrients, but this has not been tested previously for marine plant–herbivore interactions. We investigated the separate and interactive effects of plant density, nutrient availability, and herbivore grazing on the phlorotannin (polyphenolic) production in the brown seaweed Ascophyllum nodosum. Seaweed plants grown at low or high densities were exposed either to nutrient enrichment, herbivorous littorinid gastropods ( Littorina obtusata), or a combination of nutrients and herbivores in an outdoor mesocosm experiment for 2 weeks. Seaweeds grown at a low density tended to have higher tissue nitrogen content compared to plants grown at a high density when exposed to elevated nutrient levels, indicating that there was a density dependent competition for nitrogen. Herbivore grazing induced a higher phlorotannin content in plants grown under ambient, but not enriched, nutrient levels, indicting either that phlorotannin plasticity is more costly when nutrients are abundant or that plants responded to herbivory by compensatory growth. However, there were no significant interactive or main effects of plant density on the seaweed phlorotannin content. The results indicate that plants in both high and low densities induce chemical defence, and that eutrophication may have indirect effects on marine plant–herbivore interactions through alterations of plant chemical defence allocation. [ABSTRACT FROM AUTHOR]

1 Terrestrial plants can sense and respond to herbivory, which may lead to increased resistance towards further grazing if the responses have negative effects on the preference and/or performance of the herbivores. Marine plants (seaweeds) are exposed to a considerable grazing pressure by herbivores ranging from large, mobile fishes and sea urchins to small, sedentary crustaceans and molluscs. The number of investigations studying induced resistance in seaweeds has increased during the last decade, but empirical results are conflicting. 2 We performed a categorical meta-analysis to evaluate statistically the overall seaweed responses to damage or damage-related cues, and factors that may explain the observed variation in inducible seaweed resistance to herbivores. 3 We found a highly significant overall effect of damage on induced seaweed resistance to further herbivory. Division of the studies into different categories showed that brown and green, but not red, seaweeds induce significant resistance to further grazing in response to grazing by small crustaceans and gastropods, but not in response to large gastropods and sea urchins. The seaweeds showed stronger responses when exposed to damage for 11–20 days than in shorter or longer experiments. 4 Seaweeds are very important both as habitat and food for a wide range of marine animals. Our findings contribute importantly to the general ecological understanding of marine plant–herbivore interactions by showing that induced resistance in seaweeds is more common than previously assumed. Many recent marine investigations included in this study have not put emphasis on the ecological relevance and underlying mechanisms of the investigated plant–herbivore interactions. We suggest that the scientific value of future investigations concerning induced defences in marine algae would benefit from formulating more advanced and/or complex hypotheses including the genetic and biochemical mechanisms, cost and constraints of damage-induced civilian and defensive seaweed responses, as well as the effects of these responses on herbivores and other organisms/trophic levels, and on community structure and functioning. [ABSTRACT FROM AUTHOR]

Herbivory on marine macroalgae (seaweeds) in temperate areas is often dominated by relatively small gastropods and crustaceans (mesoherbivores). The effects of these herbivores on the performance of adult seaweeds have so far been almost exclusively investigated under artificial laboratory conditions. Furthermore, several recent laboratory studies with mesoherbivores indicate that inducible chemical resistance may be as common in seaweeds as in vascular plants. However, in order to further explore and test the possible ecological significance of induced chemical resistance in temperate seaweeds, data are needed that address this issue in natural populations. We investigated the effect of grazing by littorinid herbivorous snails ( Littorina spp.) on the individual net growth of the brown seaweed Ascophyllum nodosum in natural field populations. Furthermore, the capacity for induced resistance in the seaweeds was assessed by removing herbivores and assaying for relaxation of defences. We found that ambient densities of gastropod herbivores significantly reduced net growth by 45% in natural field populations of A. nodosum. Seaweeds previously exposed to grazing in the field were less consumed by gastropod herbivores in feeding bioassays. Furthermore, the concentration of phlorotannins (polyphenolics), which have been shown to deter gastropod herbivores, was higher in the seaweeds that were exposed to gastropod herbivores in the field. This field study corroborates earlier laboratory experiments and demonstrates that it is important to make sure that the lack of experimental field data on marine mesoherbivory does not lead to rash conclusions about the lack of significant effects of these herbivores on seaweed performance. The results strongly suggest that gastropods exert a significant selection pressure on the evolution of defensive traits in the seaweeds, and that brown seaweeds can respond to attacks by natural densities of these herbivores through increased chemical resistance to further grazing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The success of introduced species is often attributed to release from co-evolved enemies in the new range and a subsequent decreased allocation to defense (EICA), but these hypotheses have rarely been evaluated for systems with low host-specificity of enemies. Here, we compare herbivore utilization of the brown seaweed, Fucus evanescens, and its coexisting competitors both in its native and new ranges, to test certain predictions derived from these hypotheses in a system dominated by generalist herbivores. While F. evanescens was shown to be a preferred host in its native range, invading populations supported a less diverse herbivore fauna and it was less preferred in laboratory choice experiments with important herbivores, when compared to co-occurring seaweeds. These results are consistent with the enemy release hypothesis, despite the fact that the herbivore communities in both regions were mainly composed of generalist species. However, in contrast to the prediction of EICA, analysis of anti-grazing compounds indicated a higher allocation to defense in introduced compared to native F. evanescens. The results suggest that the invader is subjected to less intense enemy control in the new range, but that this is due to an increased allocation to defense rather than release from specialized herbivores. This indicates that increased resistance to herbivory might be an important strategy for invasion success in systems dominated by generalist herbivores. [ABSTRACT FROM AUTHOR]

Brown seaweeds can serve as habitat and food for a number of mesoherbivore species, but the effect of mesoherbivore grazing on the fitness of individual seaweed plants is not well documented. Here we investigate how mechanical wounding, which mimics the grazing damage made by the herbivorous gastropod Littorina obtusata, affects the biomass change, apical growth, and individual shoot strength of the fucoid seaweed species Ascophyllum nodosum both in natural field populations and in the laboratory. We did not detect a significant effect of wounding on apical shoot growth in the laboratory, but wounding decreased the plant biomass in half of the studied A. nodosum populations in the field. Furthermore, we found that the strength of individual A. nodosum shoots was significantly lower when compared with unwounded control shoots initially after wounding. However, after 11 days incubation in the laboratory, the strength of the wounded shoots had increased almost to the level of the control shoots, although there was still a significant difference in the force required to break the shoots. These results indicate that wounding can increase the tissue loss (and thereby decrease the fitness) of A. nodosum plants in natural populations, probably through weakening of individual shoots. However, A. nodosum appears to have a mechanism to strengthen the shoots after mechanical wounding, and therefore, the timing of damage (e.g. prior to a storm) probably determines the amount of plant tissue lost through wave-induced forces. [ABSTRACT FROM AUTHOR]

Optimal Defense Theory predicts that plants exposed to herbivory should allocate more resources to produce costly secondary metabolites in tissues with higher fitness values. To increase plant resistance, the secondary metabolites must have a negative impact on the preference and/or performance of herbivores. We tested the hypotheses that induction of secondary metabolites (phlorotannins) in a brown seaweed in response to grazing by herbivorous gastropods will differ between seaweed tissues with different fitness values (basal stipes and annual shoots), and that the subsequent change in food value will affect the fitness (growth and fecundity) of the gastropods. Induction of phlorotannins was significant in both tissue types but was more pronounced in basal stipes, which have a higher fitness value. Basal tissues also had significantly higher constitutive defense levels than did apical tissues. No effects of algal tissue type or grazing history on the growth rate of the gastropods were detected. However, the number of viable eggs was significantly lower for gastropods feeding on basal shoots, and there was a significantly lower proportion of viable eggs produced by gastropods that were offered previously grazed seaweed tissues. The results show that induced resistance, and its variation among different plant parts, can have significant negative effects on herbivore performance that may reduce future herbivore pressure and thus enhance plant fitness. [ABSTRACT FROM AUTHOR]

It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus. [ABSTRACT FROM AUTHOR]

Examines the prediction of optimal defense theory on the intraplant variation in defense levels. Morphological defenses of living organisms; Differences in sums of elasticity values among the growth, stasis and fertility regions; Development of the field of matrix population models.

The habitat and feeding preference of two gastropod mesoherbivore species, Ansates (Helcion) pellucida and Lacuna vincta, inhabiting the kelp Laminaria hyperborea were investigated by studying the distribution, habitat choice and food preference of the herbivores between new and old kelp fronds. Nitrogen content and chemical defence (phlorotannin) level of the kelp fronds were measured in order to determine whether they were correlated with the feeding preference of the herbivores. The habitat choice of Lacuna vincta was correlated with the food preference of this species, while the habitat choice of A. pellucida probably was due to some other factor, e.g. competition or mortality. Ansates pellucida preferred to reside on the old fronds of Laminaria hyperborea, but consumed an equal amount of both tissue types. Lacuna vincta, however, preferred the new Laminaria hyperborea fronds both as habitat and food. There was a large variation in the phlorotannin content among the tissue samples of L. hyperborea. However, there were no overall statistically significant differences in tissue nitrogen or phlorotannin content between the new and the old L. hyperborea fronds. [ABSTRACT FROM PUBLISHER]