Ecological lever and interface ecology: epibiosis modulates the interactions between host and environment

Stonefish (Synanceia spp.) Ichthyocrinotoxins: An ecological review and prospectus for future research and biodiscovery

Marine organisms possess a diverse array of unique substances, many with wide ranging potential for applications in medicine, industry, and other sectors. Stonefish (Synanceia spp.), a bottom-dwelling fish that inhabit shallow and intertidal waters throughout the Indo-Pacific, harbour two distinct substances, a venom, and an ichthyocrinotoxin. Stonefish are well-known for the potent venom associated with their dorsal spines as it poses a significant risk to public health. Consequently, much of the research on stonefish focusses on the venom, with the aim of improving outcomes in cases of envenomation. However, there has been a notable lack of research on stonefish ichthyocrinotoxins, a class of toxin that is synthesised within specialised epithelial cells (i.e., tubercles) and exuded onto the skin. This has resulted in a substantial knowledge gap in our understanding of these animals. This review aims to bridge this gap by consolidating literature on the ecological functions and biochemical attributes of ichthyocrinotoxins present in various fish species and juxtaposing it with the current state of knowledge of stonefish ecology. We highlight the roles of ichthyocrinotoxins in predator defence, bolstering innate immunity, and mitigating integumentary interactions with parasites and detrimental fouling organisms. The objective of this review is to identify promising research avenues that could shed light on the ecological functions of stonefish ichthyocrinotoxins and their potential practical applications as therapeutics and/or industrial products.

A survey of epibiont hydrozoans on Sargassum

The brown alga Sargassum provides a natural substrate occupied by hydrozoans in shallow marine waters. A global count in 2007 listed 39 epibiotic species of Hydrozoa growing on Sargassum, but more studies have been published since, therefore, an update is timely, particularly due to the increased abundance of Sargassum in the Caribbean. This review, based on a recent literature survey and new records from Mexico, includes 133 publications of epibiotic hydrozoans on Sargassum spanning 220 years, from 1802 to 2022. A total of 131 hydrozoan species were recorded on 26 species of Sargassum, most belonging to the subclass Hydroidolina (130), with only one record of a trachyline medusa (Gonionemus vertens, subclass Trachylinae). Most publications centered on the Tropical Atlantic, where the greatest number of hydrozoan species (67 species) were recorded. All hydrozoan species possess a hydrorhiza, except one hydromedusae species that attach to Sargassum via adhesive tentacles. Most of the hydrozoan species associated with Sargassum exhibited a benthic life cycle (93 species) and are comprised of erect, branched colonies (67 species) and large hydrothecae (69 species). Although the number of studies of epibiotic hydrozoans on Sargassum has increased since the mid-20th century, nevertheless hydrozoan richness has not reached an asymptote. Therefore, more sampling of Sargassum species would likely identify more hydrozoan species associated with Sargassum, especially among benthic Sargassum, and might help reveal potential biogeographical and ecological patterns between Sargassum and hydrozoan epibionts.

Thermal stress gradient causes increasingly negative effects towards the range limit of an invasive mussel

Environmental filtering (EF), the abiotic exclusion of species, can have first order, direct effects with cascading consequences for population dynamics, especially at range edges where abiotic conditions are suboptimal. Abiotic stress gradients associated with EF may also drive indirect second order effects, including exacerbating the effects of competitors, disease, and parasites on marginal populations because of suboptimal physiological performance. We predicted a cascade of first and second order EF-associated effects on marginal populations of the invasive mussel Mytilus galloprovincialis, plus a third order effect of EF of increased epibiont load due to second order shell degradation by endoliths. Mussel populations on rocky shores were surveyed across 850 km of the south-southeast coast of South Africa, from the species' warm-edge range limit to sites in the centre of their distribution, to quantify second order (endolithic shell degradation) and third order (number of barnacle epibionts) EF-associated effects as a function of along-shore distance from the range edge. Inshore temperature data were interpolated from the literature. Using in situ temperature logger data, we calculated the effective shore level for several sites by determining the duration of immersion and emersion. Summer and winter inshore water temperatures were linked to distance from the mussel's warm range edge (our proxy for an EF-associated stress gradient), suggesting that seasonality in temperature contributes to first order effects. The gradient in thermal stress clearly affected densities, but its influence on mussel size, shell degradation, and epibiosis was weaker. Relationships among mussel size, shell degradation, and epibiosis were more robust. Larger, older mussels had more degraded shells and more epibionts, with endolithic damage facilitating epibiosis. EF associated with a gradient in thermal stress directly limits the distribution, abundance, and size structure of mussel populations, with important indirect second and third order effects of parasitic disease and epibiont load, respectively.

Body condition and energy content of the shore crab Carcinus maenas L. in a temperate coastal system: the cost of barnacle epibiosis

The impact of barnacle epibionts on the condition of the shore crab Carcinus maenas was studied for the western Wadden Sea population. Approximately 39% of the crabs were fouled with the barnacle Balanus crenatus. Although the morphological Fulton's K condition decreased by 5.8% in fouled crabs, Linear Mixed-Effects Models (LMM) showed that only the energetic condition of the crabs was significantly affected by fouling. The energy density of fouled crabs was consistently poorer (4.1% in AFDW; 8.7% in dry weight) than that of non-fouled crabs, especially in females and green forms in dry weight (12.8% and 11.4% reduction, respectively). Cumulative infection with Sacculina carcini, detected in 4.5% of the fouled crabs, additionally reduced by 14.3% the energy density in dry weight and almost to half of the total energy of the fouled crabs. Impacts of energy density reduction on crabs' growth and reproduction are discussed.

Ecological biomechanics of damage to macroalgae

Macroalgae provide food and habitat to a diversity of organisms in marine systems, so structural damage and breakage of thallus tissue can have important ecological consequences for the composition and dynamics of marine communities. Common sources of macroalgal damage include breakage by hydrodynamic forces imposed by ambient water currents and waves, tissue consumption by herbivores, and injuries due to epibionts. Many macroalgal species have biomechanical designs that minimize damage by these sources, such as flexibly reconfiguring into streamlined shapes in flow, having either strong or extensible tissues that are tough, and having chemical and morphological defenses against herbivores and epibionts. If damage occurs, some macroalgae have tissue properties that prevent cracks from propagating or that facilitate tissue breakage in certain places, allowing the remainder of the thallus to survive. In contrast to these mechanisms of damage control, some macroalgae use breakage to aid dispersal, while others simply complete their reproduction prior to seasonally-predictable periods of damage (e.g., storm seasons). Once damage occurs, macroalgae have a variety of biomechanical responses, including increasing tissue strength, thickening support structures, or altering thallus shape. Thus, macroalgae have myriad biomechanical strategies for preventing, controlling, and responding to structural damage that can occur throughout their lives.

Ecological biomechanics of marine macrophytes

Macroalgae and seagrasses in coastal habitats are exposed to turbulent water currents and waves that deform them and can rip them off the substratum, but that also transport essential water-borne substances to them and disperse their propagules and wastes. Field studies of the physical environment, ecological interactions, and life history strategies of marine macrophytes reveal which aspects of their biomechanical performance are important to their success in different types of natural habitats and enable us to design ecologically relevant laboratory experiments to study biomechanical function. Morphology and tissue mechanical properties determine the hydrodynamic forces on macrophytes and their fate when exposed to those forces, but different mechanical designs can perform well in the same biophysical habitat. There is a trade-off between maximizing photosynthesis and minimizing breakage, and some macrophytes change their morphology in response to environmental cues. Water flow in marine habitats varies on a wide range of temporal and spatial scales, so diverse flow microhabitats can occur at the same site. Likewise, the size, shape, and tissue material properties of macrophytes change as they grow and age, so it is important to understand the different physical challenges met by macrophytes throughout their lives.

Epibiont assemblages on limpet shells: Biodiversity drivers in intertidal rocky shores

Limpet shells can harbour a high diversity of species. Individuals of four limpet species (Patella depressa, Patella ulyssiponensis, Patella vulgata and Siphonaria pectinata) were collected monthly during one year in southern Portugal. Epibiont organisms were identified, counted and the percentage cover of facilitator taxa was also recorded. A total of 86 taxa were identified with abundance reaching 674 epibionts on a single basibiont shell. P. ulyssiponensis showed the highest epibiont species diversity and richness while P. depressa and P. vulgata showed similar diversity and richness. P. depressa had a more even epibiotic community mainly due to higher densities of Chthamalus sp. Overall, basibiont species was the key factor determining the epibiotic community, followed by month/season and erect algae. The presence of erect algae potentiated the epibionts diversity on limpet shells, whereas the occurrence of barnacles tended to decrease it and the presence of crustose algae had no significant effect on epibionts diversity. These findings shed further light on the biological and ecological complex relationships among keystone species inhabiting intertidal rocky shores.

A mesocosm study on bacteria-kelp interactions: Importance of nitrogen availability and kelp genetics

Macroalgal holobiont studies involve understanding interactions between the host, its microbiota, and the environment. We analyzed the effect of bacteria-kelp interactions on phenotypic responses of two genetically distinct populations of giant kelp, Macrocystis pyrifera (north and south), exposed to different nitrogen (N) concentrations. In co-culture experiments with different N concentration treatments, we evaluated kelp growth responses and changes in three specific molecular markers associated with the N cycle, both in epiphytic bacteria (relative abundance of nrfA-gene: cytochrome c nitrite reductase) and macroalgae (expression of NR-gene: nitrate reductase; GluSyn-gene: glutamate synthase). Both kelp populations responded differently to N limitation, with M. pyrifera-south sporophytes having a lower specific growth rate (SGR) under N-limiting conditions than the northern population; M. pyrifera-north sporophytes showed no significant differences in SGR when exposed to low-N and high-N concentrations. This corresponded to a higher GluSyn-gene expression in the M. pyrifera-north sporophytes and the co-occurrence of specific nrfA bacterial taxa. These bacteria may increase ammonium availability under low-N concentrations, allowing M. pyrifera-north to optimize nutrient assimilation by increasing the expression of GluSyn. We conclude that bacteria-kelp interactions are important in enhancing kelp growth rates under low N availability, although this effect may be regulated by the genetic background of kelp populations.

Association of the alga Cladogonium sp. with a multifactorial disease outbreak in dwarf shrimp (Neocaridina davidi)

This study outlines a multifactorial disease outbreak in a population of the freshwater shrimp Neocaridina davidi, with the focus on a rarely described parasitic alga. Within this multifactorial disease outbreak, low but consistent mortality was observed. During microscopic examination, an infection of the shrimp with bacterial and fungal-like agents was diagnosed. Furthermore, the green alga Cladogonium sp. was found in pleopodal regions. The alga compromised the body surface of the shrimp, and its rhizoids penetrated the chitin shell and reached into the subcutaneous tissue. This might be a first indication of a parasitic lifestyle. In addition to a morphological description, sequencing data are presented which allow the taxonomic classification of the organism within the order Trentepohliales.

Role of bioactive metabolites from Acremonium camptosporum associated with the marine sponge Aplysina fulva

Acremonium camptosporum, a fungus associated with the marine sponge Aplysina fulva, was collected from the isolated mid-Atlantic Saint Peter and Saint Paul Archipelago, Brazil, and was found to produce secondary metabolites that displayed antibacterial activities. Mass spectra data obtained by UPLC-ESI-MS/MS analyses of these extracts were compared to several databases and revealed the presence of several different cytotoxic acremonidins and acremoxanthones. The close association between the sponge and the fungi with its compounds could be of strategic importance in defending both from the high predation pressure and spatial competition in the warm-water scarps of the islands.

Climate change transforms the functional identity of Mediterranean coralligenous assemblages

Quantifying changes in functional community structure driven by disturbance is critical to anticipate potential shifts in ecosystem functioning. However, how marine heatwaves (MHWs) affect the functional structure of temperate coral-dominated communities is poorly understood. Here, we used five long-term (> 10 years) records of Mediterranean coralligenous assemblages in a multi-taxa, trait-based analysis to investigate MHW-driven changes in functional structure. We show that, despite stability in functional richness (i.e. the range of species functional traits), MHW-impacted assemblages experienced long-term directional changes in functional identity (i.e. their dominant trait values). Declining traits included large sizes, long lifespans, arborescent morphologies, filter-feeding strategies or calcified skeletons. These traits, which were mostly supported by few sensitive and irreplaceable species from a single functional group (habitat-forming octocorals), disproportionally influence certain ecosystem functions (e.g. 3D-habitat provision). Hence, MHWs are leading to assemblages that are deficient in key functional traits, with likely consequences for the ecosystem functioning.

Citizen science via social media revealed conditions of symbiosis between a marine gastropod and an epibiotic alga

Environmental factors promote symbiosis, but its mechanism is not yet well understood. The alga Pseudocladophora conchopheria grows only on the shell of an intertidal gastropod Lunella correensis, and these species have a close symbiotic relationship which the alga reduces heat stress of the gastropod. In collaboration with general public, we investigated how environmental conditions alter the symbiotic interaction between the alga and the gastropod. Information about the habitats of each gastropod and images of shells was obtained from the Japanese and Korean coasts via social media. We constructed the hierarchical Bayesian model using the data. The results indicated that the proportion of shell area covered by P. conchopheria increased as the substrate size utilized by the gastropod increased. Meanwhile, temperature did not affect the proportion of P. conchopheria on the shell. These suggested that the alga provides no benefits for the gastropod on small substrates because gastropod can reduce the heat stress by diving into the small sediment. Further, the gastropod's cost incurred by growing the alga on the shell seems to be low as the algae can grow even in cooler places where no benefits of heat resistance for gastropods. Different environments can yield variable conditions in symbiosis.

Antimicrobial compounds produced by Lysinibacillus odysseyi epiphytic bacteria associated with red algae

Seaweed epiphytic bacteria are highly host specific and their association is little known. The marine environment of Andaman Islands is rich in algal diversity and their association with microbial communities remains unexplored. We investigated the epiphytic bacterial communities from the intertidal red alga Gracilaria canaliculata. A total of four epiphytic bacterial isolates were cultured and screened for antimicrobial activity. Of the four isolates, one potential isolate, Gr102, exhibited strong antimicrobial activity in 0.50 μg/ml concentration against enteropathogenic Escherichia coli, Klebsiella pneumoniae, and Shigella flexneri. This potential isolate was characterized by genomic sequencing, fatty acid methyl ester analysis, and matrix-assisted laser desorption ionization-time of flight spectrometry, and the strain Gr102 was identified as Lysinibacillus odysseyi KC149512. Purified fractions obtained were analyzed by gas chromatography and mass spectrometry. Antimicrobial compounds such as furan, lupenol, diazene, and butenyl methyl ketone were identified. Based on the high level of activity, red algae epiphytic bacteria are potential sources of producing bioactive secondary metabolites.

Biodiversity of carapace epibiont diatoms in loggerhead sea turtles (Caretta caretta Linnaeus 1758) in the Aegean Sea Turkish coast

Background

The Aegean Sea coast of Turkey hosts one of the most important nesting grounds for loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea. Previous studies have revealed that the sea turtle carapace provides favourable conditions for various epibiontic organisms. Epibionts occurring on the carapace have been examined from different locations in the oceans.

Methods

This is the first time such a high number (39) of samples collected from nesting turtles during such a long time period (extending from 2011 to 2018) has been used for the study of the diatom component of the microbiome on the turtle carapaces. A total of 33 samples were investigated in terms of light microscopy (LM) and scanning electron microscopy (SEM). Six unprocessed biofilm fragments were subject to SEM observations.

Results

A total of 457 epizoic diatom taxa belonging to 86 genera were identified. Epizoic forms, e.g., Achnanthes spp., Chelonicola spp. or Tripterion spp. (also identified by SEM observations of the undisturbed pieces of the microbiome) dominated in terms of relative abundance, but the highest numbers of taxa were ubiquitously represented by Navicula (79), Nitzschia (45), Amphora (40), Cocconeis (32), Diploneis (25) and Mastogloia (23). Navicula perminuta and Delphineis australis were the most frequent taxa, present in 65% of the samples, both with an average relative abundance of 10%. The results of our study revealed that diatoms are an essential component of the loggerhead sea turtles’ microbiome, in terms of high biodiversity and abundance. Although strict epibionts provide a signature of the turtle microbiome, the carapace as a solid substrate attracts numerous benthic diatom species which are considered opportunistic forms and can be found in the surrounding benthic habitats of the vast ocean littoral space.

Passenger for millenniums: association between stenothermic microcrustacean and suctorian epibiont - the case of Eurytemora lacustris and Tokophyra sp

Epibionts often colonize the exoskeleton of crustaceans, which sometimes results in the development of a long-term relationship between them. Our present work confirmed that a specific epibiont is closely associated with the pelagic calanoid copepod Eurytemora lacustris, regardless of the region, which suggests a preserved interaction between these species. Molecular analyses revealed that the epibiont belongs to the genus Tokophrya. We also found that the level of basibiont colonization is related to its size and identified that the most intensely inhabited body parts are those located near the center of the copepod body. We hypothesize that the relationship between Eurytemora (basibiont) and Tokophrya (epibiont) was established during the Quaternary period, following which these two populations were fragmented into lakes where they survived in close interaction. In addition, we suppose that the close relationship between the two species indicates the coevolution of stenotherms. Further studies on the interactions between Eurytemora lacustris and Tokophrya are required in order to gain insight into the long-term relationship between the copepods and the epibionts.

The Cost for Biodiversity: Records of Ciliate–Nematode Epibiosis with the Description of Three New Suctorian Species

Epibiosis is a common phenomenon in marine systems. In marine environments, ciliates are among the most common organisms adopting an epibiotic habitus and nematodes have been frequently reported as their basibionts. In the present study, we report several new records of peritrich and suctorian ciliates-nematode association worldwide: from a deep-sea pockmark field in the NW Madagascar margin (Indian Ocean), from a shallow vent area in the Gulf of Naples (Mediterranean, Tyrrhenian Sea), in a MPA area in the Gulf of Trieste (Mediterranean, Adriatic Sea), from a mangrove system in French Guiana (South America, Atlantic Ocean), and from the Maldivian Archipelago. In addition, three new species of Suctorea from the Secca delle Fumose shallow vent area (Gulf of Naples) were described: Loricophrya susannae n. sp., Thecacineta fumosae n. sp. and Acinetopsis lynni n. sp. In the light of these new records and data from the existing literature, we discuss the suctorian–nematode epibiosis relationship as a lever to biodiversity.

Environmental drivers of rhodolith beds and epiphytes community along the South Western Atlantic coast

Environmental conditions shape the occurrence and abundance of habitat-building organisms at global scales. Rhodolith beds structure important hard substrate habitats for a large number of marine benthic organisms. These organisms can benefit local biodiversity levels, but also compete with rhodoliths for essential resources. Therefore, understanding the factors shaping the distribution of rhodoliths and their associated communities along entire distributional ranges is of much relevance for conservational biology, particularly in the scope of future environmental changes. Here we predict suitable habitat areas and identify the main environmental drivers of rhodoliths' variability and of associated epiphytes along a large-scale latitudinal gradient. Occurrence and abundance data were collected throughout the South-western Atlantic coast (SWA) and modelled against high resolution environmental predictors extracted from Bio-Oracle. The main drivers for rhodolith occurrence were light availability and temperature at the bottom of the ocean, while abundance was explained by nitrate, temperature and current velocity. Tropical regions showed the highest abundance of rhodoliths. No latitudinal pattern was detected in the variability of epiphytes abundance. However, significant differences were found between sampled sites regarding the composition of predominant taxa. The predictors influencing such differences were temperature and nitrate. The Tropical region is abundant in species with warm-water affinities, decreasing toward warm temperate region. The expressive occurrence of tropical species not referred before for warm temperate beds indicate a plausible tropicalization event.

Salinity and Time Can Alter Epibacterial Communities of an Invasive Seaweed

The establishment of epibacterial communities is fundamental to seaweed health and fitness, in modulating ecological interactions and may also facilitate adaptation to new environments. Abiotic factors like salinity can determine bacterial abundance, growth and community composition. However, influence of salinity as a driver of epibacterial community composition (until species level) has not been investigated for seaweeds and especially under long time scales. We also do not know how abiotic stressors may influence the 'core' bacterial species of seaweeds. Following an initial (immediately after field collection) sampling of epibacterial community of an invasive red seaweed Agarophyton vermicullophylum, we conducted a long term mesocosm experiment for 5 months, to examine the influence of three different salinities (low, medium and high) at two different time points (3 months after start of experiment and 5 months, i.e., at the end of experiment) on the epibacterial community richness and composition of Agarophyton. Metagenomic sequencing showed that epibacterial communities changed significantly according to salinity and time points sampled. Epibacterial richness was significantly different between low and high salinities at both time points. Epibacterial richness also varied significantly between 3 months (after start of experiment) and 5 months (end of experiment) within low, medium and high salinity level. Irrespective of salinity levels and time points sampled 727 taxa consistently appeared in all Agarophyton samples hinting at the presence of core bacterial species on the surface of the alga. Our results indicate that both salinity and time can be major driving forces in structuring epibacterial communities of seaweeds with respect to richness and β-diversity. We highlight the necessity of conducting long term experiments allowing us to detect and understand epibacterial succession over time on seaweeds.

Surface chemical defence of the eelgrass Zostera marina against microbial foulers

Plants rely on both mechanical and chemical defence mechanisms to protect their surfaces against microorganisms. The recently completed genome of the eelgrass Zostera marina, a marine angiosperm with fundamental importance for coastal ecosystems, showed that its re-adaptation from land to the sea has led to the loss of essential genes (for chemical communication and defence) and structural features (stomata and thick cuticle) that are typical of terrestrial plants. This study was designed to understand the molecular nature of surface protection and fouling-control strategy of eelgrass against marine epiphytic yeasts. Different surface extraction methods and comparative metabolomics by tandem mass spectrometry (LC-MS/MS) were used for targeted and untargeted identification of the metabolite profiles of the leaf surface and the whole tissue extracts. Desorption electrospray ionization-imaging mass spectrometry (DESI-IMS) coupled with traditional bioassays revealed, for the first time, the unique spatial distribution of the eelgrass surface-associated phenolics and fatty acids, as well as their differential bioactivity against the growth and settlement of epiphytic yeasts. This study provides insights into the complex chemical defence system of the eelgrass leaf surface. It suggests that surface-associated metabolites modulate biotic interactions and provide chemical defence and structural protection to eelgrass in its marine environment.

The impact of the sea anemone Actinothoe sphyrodeta on Mytilus galloprovincialis mussel cultivation (Galicia, Spain)

Marine mussel aggregations act as a substratum and refuge for many fouling species. Mussel cultivation in Galicia, Spain, is carried out on hanging ropes in subtidal systems. The fauna associated with this cultivation includes a large number of invertebrates that compete for space or food with the mussels, or use their clusters as a refuge from predators or water turbulence. Outbreaks of the epibiont anemone Actinothoe sphyrodeta have been reported in cultivated Galician mussels since 2013, but their impact has not been investigated rigorously. Here, the temporal and spatial variability of Actinothoe sphyrodeta on mussel shells throughout one year is presented. Sampling of mussel size, weight and byssus attachment strength allowed mussel tenacity (attachment strength relative to size) to be calculated. A higher presence of Actinothoe sphyrodeta correlated with lower mussel tenacity and greater biomass losses, suggesting that this species could be an economically important biofouling component.

New record of Epistylishentscheli (Ciliophora, Peritrichia) as an epibiont of Procambarus (Austrocambarus) sp. (Crustacea, Decapoda) in Chiapas, Mexico

Epibiosis is very common between crustaceans and ciliates where the calcified surface of the crustacean body provides a suitable substrate for ciliate colonization. The aim of this contribution is to provide data about a new record between the epistylid ciliate Epistylishentscheli Kahl, 1935, and the crayfish Procambarus (Austrocambarus) sp. The distribution of the epistylid on the basibiont body and its cellular/colonial characteristics were analyzed. Procambarus (Austrocambarus) sp. harbored colonies of E.hentscheli only on the pereiopods. This is the first record of this peritrich ciliate as an epibiont on Crustacea, having been previously found on algae and fish.

Antimicrobial Potential of Epiphytic Bacteria Associated With Seaweeds of Little Andaman, India

Seaweeds of the intertidal regions are a rich source of surface associated bacteria and are potential source of antimicrobial molecules. In the present study, 77 epiphytic isolates from eight different algae collected from Little Andaman were enumerated. On testing for their antimicrobial activities against certain pathogens twelve isolates showed positive and six of them showed significant antimicrobial inhibition zone against Shigella boydii type 1, Shigella flexneri type 2a, Shigella dysenteriae type 5, Enterotoxigenic Escherichia coli O115, Enteropathogenic E. coli serotype O114, Vibrio cholera; O1 Ogawa, Aeromonas hydrophila, Klebsiella pneumoniae, Staphylococcus aureus. Based on the activity these six isolates (G1C, G2C, G3C, UK, UVAD, and Tor1) were identified by 16S rRNA gene sequence and were found to belong to the phyla Firmicutes and Proteobacteria. Purified antimicrobial compounds obtained from these isolates were identified by GC-MS. Furan derivatives were identified from G2C Pseudomonas stutzeri KJ849834, UVAD Alcanivorax dieselolei KJ849833, UK Vibrio sp. KJ849837, Tor1 Exiguobacterium profundum KJ849838. While 2-Pyrrolidinone, Phenol, 2, 4-bis (1, 1-dimethylethyl) were from G3C Vibrio owensii KJ849836 and (1-Allylcyclopropyl) methanol from the extracts of G1C Bacillus sp. KJ849835. The results of the present study shows that these six potent isolates isolated from the seaweeds are found to be a source of antimicrobial compounds.

The role of chemical antifouling defence in the invasion success of Sargassum muticum: A comparison of native and invasive brown algae

Competition and fouling defence are important traits that may facilitate invasions by non-indigenous species. The 'novel weapons hypothesis' (NWH) predicts that the invasive success of exotic species is closely linked to the possession of chemical defence compounds that the recipient community in the new range is not adapted to. In order to assess whether chemical defence traits contribute to invasion success, anti-bacterial, anti-quorum sensing, anti-diatom, anti-larval and anti-algal properties were investigated for the following algae: a) the invasive brown alga Sargassum muticum from both, its native (Japan) and invasive (Germany) range, b) the two non- or weak invasive species Sargassum fusiforme and Sargassum horneri from Japan, and c) Fucus vesiculosus, a native brown alga from Germany. Crude and surface extracts and lipid fractions of active extracts were tested against common fouling organisms and zygotes of a dominant competing brown alga. Extracts of the native brown alga F. vesiculosus inhibited more bacterial strains (75%) than any of the Sargassum spp. (17 to 29%). However, Sargassum spp. from Japan exhibited the strongest settlement inhibition against the diatom Cylindrotheca closterium, larvae of the bryozoan Bugula neritina and zygotes of the brown alga F. vesiculosus. Overall, extracts of S. muticum from the invasive range were less active compared to those of the native range suggesting an adaptation to lower fouling pressure and competition in the new range resulting in a shift of resource allocation from costly chemical defence to reproduction and growth. Non-invasive Sargassum spp. from Japan was equally defended against fouling and competitors like S. muticum from Japan indicating a necessity to include these species in European monitoring programs. The variable antifouling activity of surface and crude extracts highlights the importance to use both for an initial screening for antifouling activity.

Minireview: algal natural compounds and extracts as antifoulants

Marine biofouling is a paramount phenomenon in the marine environment and causes serious problems to maritime industries worldwide. Marine algae are known to produce a wide variety of chemical compounds with antibacterial, antifungal, antialgal, and anti-macrofouling properties, inhibiting the settlement and growth of other marine fouling organisms. Significant investigations and progress have been made in this field in the last two decades and several antifouling extracts and compounds have been isolated from micro- and macroalgae. In this minireview, we have summarized and evaluated antifouling compounds isolated and identified from macroalgae and microalgae between January 2010 and June 2016. Future directions for their commercialization through metabolic engineering and industrial scale up have been discussed. Upon comparing biogeographical regions, investigations from Southeast Asian waters were found to be rather scarce. Thus, we have also discussed the need to conduct more chemical ecology based research in relatively less explored areas with high algal biodiversity like Southeast Asia.

Identification of rosmarinic acid and sulfated flavonoids as inhibitors of microfouling on the surface of eelgrass Zostera marina

A bioassay-guided approach was used to identify defense compounds that are present on the surface of Zostera marina and which inhibit settlement of microfoulers at natural concentrations. Moderately polar eelgrass surface extracts inhibited the settlement of seven marine bacteria and one yeast that originated from non-living substrata. In contrast, five other bacterial strains that had been directly isolated from eelgrass surfaces were all insensitive, which suggested a selective effect of surface metabolites on the microbial communities present on eelgrass. Bioassay-guided isolation of active compounds from the extracts in combination with UPLC-MS and 1H-NMR spectroscopy resulted in the identification of rosmarinic acid, luteolin-7-sulfate and diosmetin-7-sulfate or its isomer chrysoeriol-7-sulfate. All three compounds are nontoxic repellents, as they did not inhibit bacterial growth, but prevented bacterial settlement in a dose-dependent manner. Between 15.6 and 106.8 μg ml-1 of rosmarinic acid were present on the eelgrass surface, enough for half maximal settlement inhibition of bacteria.

Epiphytic Planctomycetes communities associated with three main groups of macroalgae

Planctomycetes, a unique group of widespread and understudied bacteria, are known to be associated with macroalgae. The temporal dynamics and the host-specific association of planctomycetal communities on Fucus spiralis, Ulva sp. and Chondrus crispus from two locations in the North Coast of Portugal were assessed both by denaturing gradient gel electrophoresis with group-specific primers and 16S rDNA amplicon libraries. The epiphytic planctomycetal communities showed a significant association with the host macroalgal species independently of the geographical location and the season. This pattern was confirmed by clone libraries of winter and summer samples: we obtained 720 16S rRNA gene sequences that represented 44 operational taxonomic units (OTUs) within the phylum Planctomycetes. Most of the OTUs belonged to Blastopirellula, followed by Rhodopirellula, Planctomyces, the Pir4 lineage and the uncultured class OM190 (this last one nearly 30% of the OTUs). Ulva sp. and C. crispus had more diverse planctomycetal communities than F. spiralis. Analysis of beta diversity showed that the planctomycetal microbiome was host specific. We hypothesize that the specific association of Planctomycetes and their macroalgal hosts is likely determined by nutritional molecules provided by the algae and the set of sulfatases inherent to each Planctomycetes species.

A New Deep-Sea Suctorian-Nematode Epibiosis (Loricophrya-Tricoma) from the Blanes Submarine Canyon (NW Mediterranean)

During a pluri-disciplinary study carried out within the frame of the Spanish research project DOS MARES, multicore samples were collected along the Blanes submarine canyon and its adjacent open slope to study the structure and dynamics of the meiofaunal organisms, mainly nematodes. Among the 5808 nematode individuals identified, only 190 of them belonged to the genus Tricoma (Desmoscolecidae), and only two harboured epibiont suctorian ciliates. The three specimens were located near the tail of the basibionts. A careful examination of the ciliates revealed that they were suctorians, which are here described as a new species of Loricophrya, namely L. mediterranea sp. nov. The new species is characterized by having a conical, slightly elongated lorica, narrowing towards posterior end; an anterior end inward curved, surrounding the lorica opening; a body placed near the lorica opening, occupying 1/3 of the lorica length, 4-8 capitate tentacles, and a peripheral, oval to sausage-shaped macronucleus. Our findings represent the first known report of an association with a deep-sea species of Tricoma, and the first record in the Mediterranean Sea, for a species of Loricophrya. The significance of the relationships between suctorian ciliates and their host in extreme environments such as deep-sea submarine canyons is discussed.

Cystophloroketals A-E, Unusual Phloroglucinol-Meroterpenoid Hybrids from the Brown Alga Cystoseira tamariscifolia

Cystophloroketals A-E (1-5), five new phloroglucinol-meroditerpenoid hybrids, have been isolated together with their putative biosynthetic precursor, the monocyclic meroditerpenoid 6, from the Mediterranean brown alga Cystoseira tamariscifolia. They represent the first examples of meroditerpenoids linked to a phloroglucinol through a 2,7-dioxabicyclo[3.2.1]octane moiety. The chemical structures, including absolute configurations, were elucidated on the basis of extensive spectroscopic analysis (HR-ESIMS, 1D and 2D NMR, and ECD) and TDDFT ECD calculations. Compounds 1-6 were tested for their antifouling activity against several marine colonizing species (bacteria, fungi, invertebrates, micro- and macroalgae). Compound 6 showed high potency for the inhibition of macrofoulers (invertebrates and macroalgae), while cystophloroketals B (2) and D (4) displayed strong inhibition of the germination of the two macroalgae tested and moderate antimicrobial activities (bacteria, microalgae, and fungi).

Large scale patterns of antimicrofouling defenses in the hard coral Pocillopora verrucosa in an environmental gradient along the Saudi Arabian coast of the Red Sea

Large scale patterns of ecologically relevant traits may help identify drivers of their variability and conditions beneficial or adverse to the expression of these traits. Antimicrofouling defenses in scleractinian corals regulate the establishment of the associated biofilm as well as the risks of infection. The Saudi Arabian Red Sea coast features a pronounced thermal and nutritional gradient including regions and seasons with potentially stressful conditions to corals. Assessing the patterns of antimicrofouling defenses across the Red Sea may hint at the susceptibility of corals to global change. We investigated microfouling pressure as well as the relative strength of 2 alternative antimicrofouling defenses (chemical antisettlement activity, mucus release) along the pronounced environmental gradient along the Saudi Arabian Red Sea coast in 2 successive years. Microfouling pressure was exceptionally low along most of the coast but sharply increased at the southernmost sites. Mucus release correlated with temperature. Chemical defense tended to anti-correlate with mucus release. As a result, the combined action of mucus release and chemical antimicrofouling defense seemed to warrant sufficient defense against microbes along the entire coast. In the future, however, we expect enhanced energetic strain on corals when warming and/or eutrophication lead to higher bacterial fouling pressure and a shift towards putatively more costly defense by mucus release.

Defence chemistry modulation by light and temperature shifts and the resulting effects on associated epibacteria of Fucus vesiculosus

The goals of this study were (1) to investigate whether Fucus vesiculosus regulates the production of its antifouling defence chemicals against epibacteria in response to light limitation and temperature shifts and (2) to investigate if different surface concentrations of defence compounds shape epibacterial communities. F. vesiculosus was incubated in indoor mesocosms at five different temperature conditions (5 to 25°C) and in outdoor mesocosms under six differently reduced sunlight conditions (0 to 100%), respectively. Algal surface concentrations of previously identified antifouling compounds--dimethylsulphopropionate (DMSP), fucoxanthin and proline--were determined and the bacterial community composition was characterized by in-depth sequencing of the 16S-rRNA gene. Altogether, the effect of different treatment levels upon defence compound concentrations was limited. Under all conditions DMSP alone appeared to be sufficiently concentrated to warrant for at least a partial inhibitory action against epibiotic bacteria of F. vesiculosus. In contrast, proline and fucoxanthin rarely reached the necessary concentration ranges for self-contained inhibition. Nonetheless, in both experiments along with the direct influence of temperature and light, all three compounds apparently affected the overall bacterial community composition associated with F. vesiculosus since tendencies for insensitivity towards all three compounds were observed among bacterial taxa that typically dominate those communities. Given that the concentrations of at least one of the compounds (in most cases DMSP) were always high enough to inhibit bacterial settlement, we conclude that the capacity of F. vesiculosus for such defence will hardly be compromised by shading or warming to temperatures up to 25°C.

Characterization and anti-settlement aspects of surface micro-structures from Cancer pagurus

Tuning surface and material properties to inhibit or prevent settlement and attachment of microorganisms is of interest for applications such as antifouling technologies. Here, optimization of nano- and microscale structures on immersed surfaces can be utilized to improve cell removal while reducing adhesion strength and the likelihood of initial cellular attachment. Engineered surfaces capable of controlling cellular behaviour under natural conditions are challenging to design due to the diversity of attaching cell types in environments such as marine waters, where many variations in cell shape, size and adhesion strategy exist. Nevertheless, understanding interactions between a cell and a potential substrate for adhesion, including topographically driven settlement cues, offers a route to designing surfaces capable of controlling cell settlement. Biomimetic design of artificial surfaces, based upon microscale features from natural surfaces, can be utilized as model surfaces to understand cell-surface interactions. The microscale surface features of the carapace from the crustacean Cancer pagurus has been previously found to influence the rate of attachment of particular organisms when compared to smooth controls. However, the nature of microscale topographic features from C. pagurus have not been examined in sufficient detail to allow design of biomimetic surfaces. In this work, the spatial distribution, chemical composition, size and shape descriptors of microscale surface features from C. pagurus are characterized in detail for the first time. Additionally, the influence of topography from C. pagurus on the settlement of marine diatoms is examined under field conditions.

Planctomycetes and macroalgae, a striking association

Planctomycetes are part of the complex microbial biofilm community of a wide range of macroalgae. Recently, some studies began to unveil the great diversity of Planctomycetes present in this microenvironment and the interactions between the two organisms. Culture dependent and independent methods revealed the existence of a great number of species but, so far, only less than 10 species have been isolated. Planctomycetes comprise the genera Rhodopirellula, Blastopirellula, and Planctomyces, Phycisphaera and the uncultured class OM190 and some other taxa have only been found in this association. Several factors favor the colonization of macroalgal surfaces by planctomycetes. Many species possess holdfasts for attachment. The macroalgae secrete various sulfated polysaccharides that are the substrate for the abundant sulfatases produced by planctomycetes. Specificity between planctomycetes and macroalgae seem to exist which may be related to the chemical nature of the polysaccharides produced by each macroalga. Furthermore, the peptidoglycan-free cell wall of planctomycetes allows them to resist the action of several antimicrobial compounds produced by the macroalgae or other bacteria in the biofilm community that are effective against biofouling by other microorganisms. Despite the increase in our knowledge on the successful planctomycetes-macroalgae association, a great effort to fully understand this interaction is needed.

Salinity affects compositional traits of epibacterial communities on the brown macroalga Fucus vesiculosus

Epibiotic biofilms have the potential to control major aspects of the biology and ecology of their hosts. Their composition and function may thus be essential for the health of the host. We tested the influence of salinity on the composition of epibacterial communities associated with the brown macroalga Fucus vesiculosus. Algal individuals were incubated at three salinities (5, 19, and 25) for 14 days and nonliving reference substrata (stones) were included in the experiment. Subsequently, the composition of their surface-associated bacterial communities was analyzed by 454 pyrosequencing of 16S rRNA gene sequences. Redundancy analysis revealed that the composition of epiphytic and epilithic communities significantly differed and were both affected by salinity. We found that 5% of 2494 epiphytic operational taxonomic units at 97% sequence similarity were responsible for the observed shifts. Epibacterial α-diversity was significantly lower at salinity 5 but did not differ between substrata. Our results indicate that salinity is an important factor in structuring alga-associated epibacterial communities with respect to composition and/or diversity. Whether direct or indirect mechanisms (via altered biotic interactions) may have been responsible for the observed shifts is discussed.

Fluorescent epibiotic microbial community on the carapace of a Bahamian ostracod

Ostracods collected from shallow coral reefs in the Bahamas were found to exhibit blue light-stimulated orange fluorescence at night. Fluorescent spectra revealed the presence of orange fluorescence with a maximum emission at ~595 nm on the carapace of these ostracods, while scanning electron microscopy revealed a morphologically diverse microbial community covering the entire carapace of these ostracods. Pyrosequencing and cyanobacterial-specific 16S rRNA sequencing reveals that this epibiont community is highly diverse and highly variable between individual ostracods. Many species of Cyanobacteria in the orders Oscillatoriales and Chroococcales, as well as other Proteobacteria and diatom chloroplast sequences, were identified using the cyanobacterial-specific primers. While no fluorescent proteins or phycoerythrin were detected in these ostracods, it is possible that the observed orange fluorescence is the result of carotenoid fluorescence from Cyanobacteria. The microbial consortium forms an epibiotic biofilm on the carapace of these ostracods whose functions are unknown.

The Ecology of Microbial Communities Associated with Macrocystis pyrifera

Kelp forests are characterized by high biodiversity and productivity, and the cycling of kelp-produced carbon is a vital process in this ecosystem. Although bacteria are assumed to play a major role in kelp forest carbon cycling, knowledge of the composition and diversity of these bacterial communities is lacking. Bacterial communities on the surface of Macrocystis pyrifera and adjacent seawater were sampled at the Hopkins Marine Station in Monterey Bay, CA, and further studied using 454-tag pyrosequencing of 16S RNA genes. Our results suggest that M. pyrifera-dominated kelp forests harbor distinct microbial communities that vary temporally. The distribution of sequence tags assigned to Gammaproteobacteria, Alphaproteobacteria and Bacteriodetes differed between the surface of the kelp and the surrounding water. Several abundant Rhodobacteraceae, uncultivated Gammaproteobacteria and Bacteriodetes-associated tags displayed considerable temporal variation, often with similar trends in the seawater and the surface of the kelp. Bacterial community structure and membership correlated with the kelp surface serving as host, and varied over time. Several kelp-specific taxa were highly similar to other bacteria known to either prevent the colonization of eukaryotic larvae or exhibit antibacterial activities. Some of these kelp-specific bacterial associations might play an important role for M. pyrifera. This study provides the first assessment of the diversity and phylogenetic profile of the bacterial communities associated with M. pyrifera.

Seasonal variation in the antifouling defence of the temperate brown alga Fucus vesiculosus

The important role of marine epibiotic biofilms in the interactions of the host with its environment has been acknowledged recently. Previous studies with the temperate brown macroalga Fucus vesiculosus have identified polar and non-polar compounds recovered from the algal surface that have the potential to control such biofilms. Furthermore, both the fouling pressure and the composition of the epibiotic bacterial communities on this macroalga varied seasonally. The extent to which this reflects a seasonal fluctuation of the fouling control mechanisms of the host is, however, unexplored in an ecological context. The present study investigated seasonal variation in the anti-settlement activity of surface extracts of F. vesiculosus against eight biofilm-forming bacteria isolated from rockweed-dominated habitats, including replication of two populations from two geographically distant sites. The anti-settlement activity at both sites was found to vary temporally, reaching a peak in summer/autumn. Anti-settlement activity also showed a consistent and strong difference between sites throughout the year. This study is the first to report temporal variation of antifouling defence originating from ecologically relevant surface-associated compounds.

Costs and benefits of chemical defence in the Red Alga Bonnemaisonia hamifera

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.

Adaptation of the 3H-leucine incorporation technique to measure heterotrophic activity associated with biofilm on the blades of the seaweed Sargassum spp

The ecological interaction between microorganisms and seaweeds depends on the production of secondary compounds that can influence microbial diversity in the water column and the composition of reef environments. We adapted the (3)H-leucine incorporation technique to measure bacterial activity in biofilms associated with the blades of the macroalgae Sargassum spp. We evaluated (1) if the epiphytic bacteria on the blades were more active in detritus or in the biofilm, (2) substrate saturation and linearity of (3)H-leucine incorporation, (3) the influence of specific metabolic inhibitors during (3)H-leucine incorporation under the presence or absence of natural and artificial light, and (4) the efficiency of radiolabeled protein extraction. Scanning electron microscopy showed heterogeneous distribution of bacteria, diatoms, and polymeric extracellular secretions. Active bacteria were present in both biofilm and detritus on the blades. The highest (3)H-leucine incorporation was obtained when incubating blades not colonized by macroepibionts. Incubations done under field conditions reported higher (3)H-leucine incorporation than in the laboratory. Light quality and sampling manipulation seemed to be the main factors behind this difference. The use of specific metabolic inhibitors confirmed that bacteria are the main group incorporating (3)H-leucine but their association with primary production suggested a symbiotic relationship between bacteria, diatoms, and the seaweed.