Effects of sponge and barnacle encrustation on survival of the scallop <Emphasis Type="Italic">Chlamys hastata</Emphasis>

The scallop Chlamys hastata frequently carries epibionts such as sponges and barnacles on its shells. Although the scallop-sponge relationship has been characterized as a mutualism, little is known about the scallop-barnacle relationship. This study investigated the effects of sponge and barnacle encrustation on the ability of C. hastata to avoid predation by the sea star Pycnopodia helianthoides. In feeding trials, P. helianthoides caught and consumed significantly more barnacle-encrusted scallops (7.7 ± 0.8 out of 20 scallops) than scallops encrusted by either of the sponges Myxilla incrustans (4.1 ± 0.9) or Mycale adhaerens (3.0 ± 0.5). Epibiont-free scallops (5.7 ± 0.5) formed an intermediate treatment between barnacle-encrusted and sponge-encrusted scallops. Possible mechanisms by which the sponges protected the scallops were investigated in two ways: two feeding trials were videotaped to allow qualitative analysis of sea star and scallop behavior and sea star feeding responses to scallop and sponge homogenates were determined to investigate if sea stars accept scallops and sponges as prey. Sea stars displayed positive feeding responses to scallop puree 97.5% ± 1.6 of the time while only displaying positive responses to Mycale adhaerens homogenate 4.4% ± 2.0 of the time and to Myxilla incrustans homogenate 4.4% ± 2.9 of the time. The videotaped feeding trials indicated that interference with tube feet adhesion by the sponge deterred predation. Observations of both sea stars that were videotaped showed that neither avoided trying to capture sponge-encrusted scallops, and at no time was a captured scallop willingly released by the sea stars. Thus, it appears that sponges provide tactile-mechanical protection and possibly chemical or tactile camouflage in this predator/prey relationship. Finally, the effects of sponge encrustation on barnacle settlement were determined. Field experiments showed that barnacle larvae settled more frequently on epibiont-free scallops than on those with either of the two sponges, potentially protecting the scallops from an epibiont that increases the scallop’s susceptibility to predation. Handling editor: K. Martens     

A Novel Filtering Mutualism between a Sponge Host and Its Endosymbiotic Bivalves

Sponges, porous filter-feeding organisms consisting of vast canal systems, provide unique substrates for diverse symbiotic organisms. The Spongia (Spongia) sp. massive sponge is obligately inhabited by the host-specific endosymbiotic bivalve Vulsella vulsella, which benefits from this symbiosis by receiving protection from predators. However, whether the host sponge gains any benefit from this association is unclear. Considering that the bivalves exhale filtered water into the sponge body rather than the ambient environment, the sponge is hypothesized to utilize water exhaled by the bivalves to circulate water around its body more efficiently. We tested this hypothesis by observing the sponge aquiferous structure and comparing the pumping rates of sponges and bivalves. Observations of water currents and the sponge aquiferous structure revealed that the sponge had a unique canal system enabling it to inhale water exhaled from bivalves, indicating that the host sponge adapted morphologically to receive water from the bivalves. In addition, the volume of water circulating in the sponge body was dramatically increased by the water exhaled from bivalves. Therefore, this sponge-bivalve association can be regarded as a novel mutualism in which two filter-feeding symbionts promote mutual filtering rates. This symbiotic association should be called a “filtering mutualism”.     

Bitten down to size: Fish predation determines growth form of the Caribbean coral reef sponge Mycale laevis

Interactions between organisms add complexity to ecosystem function, particularly on coral reefs. The Caribbean orange icing sponge Mycale laevis is semi-cryptic, often growing under coral colonies or between coral branches. This association is reportedly a mutualism, with the sponge deterring boring sponges from invading the coral skeleton and the coral providing an expanding surface for sponge growth. But is there an alternative explanation for the proximity of sponge and coral? We examined the importance of fish predation on the growth of the sponge. While the semi-cryptic growth form of M. laevis predominates on reefs off the Florida Keys and the Bahamas Islands, M. laevis grows with a non-cryptic, erect morphology off Bocas del Toro, Panama. Surveys revealed that sponge-eating fishes were rare or absent at Bocas del Toro compared to sites in the Florida Keys. Because past studies were inconsistent about the palatability of M. laevis to fish predators, we conducted feeding experiments with sponges from all three sites. Crude organic extracts of M. laevis from all three sites were palatable to generalist fish predators in aquarium assays, and field feeding assays and caging experiments conducted in the Florida Keys confirmed that spongivorous fishes readily ate exposed fragments of M. laevis. Our results suggest that M. laevis is restricted to its semi-cryptic growth form by spongivorous predators, with corals providing a physical refuge from predation. This alternative explanation supports the broader hypothesis that Caribbean reef sponges can be categorized on the basis of chemical defense into defended, palatable, and preferred species, the last of which are restricted to refugia.     

Trophic ecology of a freshwater sponge (Spongilla lacustris) revealed by stable isotope analysis

The vital roles that sponges play in marine habitats are well-known. However, sponges inhabiting freshwaters have been largely ignored despite having widespread distributions and often high local abundances. We used natural abundance stable isotope signatures of carbon and nitrogen (δ ¹³C and δ ¹⁵N) to infer the primary food source of the cosmopolitan freshwater sponge Spongilla lacustris. Our results suggest that S. lacustris feed largely on pelagic resources and may therefore link pelagic and benthic food webs. A facultative association between S. lacustris and endosymbiotic green algae caused S. lacustris to have significantly depleted carbon and nitrogen signatures that may reflect carbon and nitrogen exchange between sponges and their symbiotic algae. Isotopic data from specialist sponge consumers demonstrated that sponges hosting zoochlorellae were the major component of the diet of the spongillafly Climacia areolaris and the sponge-eating caddisfly Ceraclea resurgens suggesting that the symbiosis between freshwater sponges and algae is important to sponge predator trophic ecology. Our results help define the role of sponges in freshwater ecosystems and shed new light on the evolution and ecological consequences of a complex tri-trophic symbiosis involving freshwater sponges, zoochlorellae, and spongivorous insects.     

Microscopical techniques reveal the in situ microbial association inside Aplysina aerophoba, Nardo 1886 (Porifera, Demospongiae, Verongida) almost exclusively consists of cyanobacteria

Sponges (Porifera) are aquatic, sessile filter feeders. As such they are permanently exposed to bacteria in the seawater. Molecular data recovered from sponges by PCR shows a high diversity in bacterial DNA. Hence, sponges are considered to live in close association with a diverse and abundant bacterial community. To recover the spatial distribution of bacteria in sponges we retrieved histological sections of Aplysina aerophoba fixed in situ. By combining signals from fluorescence in situ hybridization (FISH), light microscopy and scanning electron microscopy we revealed a detailed histological picture of the spatial organization of the sponge microbial association within the sponges. Our histological results confirm a high abundance of cyanobacteria inside A. aerophoba while other living bacteria are almost absent. This detailed insight into sponge microbiology could only be achieved by the combination of careful sample preparation and different microscopical and histological methods. It also shows the need to confirm molecular datasets in situ and with a high spatial resolution.     

Avoidance and escape responses of the gastropod mollusc Olivella biplicata (Sowerby) to predatory asteroids

The sand-dwelling gastropod Olivella biplicata (Sowerby) gives two chemically-mediated defensive responses to predatory asteroids — an avoidance and an escape response. An avoidance response is triggered by water-borne chemicals diffusing from distant starfish. When snails on the surface of the sand sense a distant predatory starfish, they avoid the predator by burying themselves in the sand. Strong avoidance responses are given to the predatory asteroids Pisaster brevispinus (Stimpson), P. ochraceus (Brandt), and Pycnopodia helianthoides (Brandt). Little or no response is given to the omnivorous asteroid Patiria miniata (Brandt) or to the predatory gastropod Polinices lewisii (Gould). An escape response is given when a snail on the surface is contacted by the starfish Pisaster brevispinus. Upon contact, the snail immediately retracts the propodium, sometimes throwing the metapodium forward at the same time; the snail then turns sharply away from the point of contact, and buries itself. Both avoidance and escape responses can be observed in the field and laboratory.     

Pyrosequencing Characterization of the Microbiota from Atlantic Intertidal Marine Sponges Reveals High Microbial Diversity and the Lack of Co-Occurrence Patterns

Sponges are ancient metazoans that host diverse and complex microbial communities. Sponge-associated microbial diversity has been studied from wide oceans across the globe, particularly in subtidal regions, but the microbial communities from intertidal sponges have remained mostly unexplored. Here we used pyrosequencing to characterize the microbial communities in 12 different co-occurring intertidal marine sponge species sampled from the Atlantic coast, revealing a total of 686 operational taxonomic units (OTUs) at 97% sequence similarity. Taxonomic assignment of 16S ribosomal RNA tag sequences estimated altogether 26 microbial groups, represented by bacterial (75.5%) and archaeal (22%) domains. Proteobacteria (43.4%) and Crenarchaeota (20.6%) were the most dominant microbial groups detected in all the 12 marine sponge species and ambient seawater. The Crenarchaeota microbes detected in three Atlantic Ocean sponges had a close similarity with Crenarchaeota from geographically separated subtidal Red Sea sponges. Our study showed that most of the microbial communities observed in sponges (73%) were also found in the surrounding ambient seawater suggesting possible environmental acquisition and/or horizontal transfer of microbes. Beyond the microbial diversity and community structure assessments (NMDS, ADONIS, ANOSIM), we explored the interactions between the microbial communities coexisting in sponges using the checkerboard score (C-score). Analyses of the microbial association pattern (co-occurrence) among intertidal sympatric sponges revealed the random association of microbes, favoring the hypothesis that the sponge-inhabiting microbes are recruited from the habitat mostly by chance or influenced by environmental factors to benefit the hosts.     

Isolation and diversity of planctomycetes from the sponge Niphates sp., seawater, and sediment of Moreton Bay, Australia

Planctomycetes are ubiquitous in marine environment and were reported to occur in association with multicellular eukaryotic organisms such as marine macroalgae and invertebrates. Here, we investigate planctomycetes associated with the marine sponge Niphates sp. from the sub-tropical Australian coast by assessing their diversity using culture-dependent and -independent approaches based on the 16S rRNA gene. The culture-dependent approach resulted in the isolation of a large collection of diverse planctomycetes including some novel lineages of Planctomycetes from the sponge as well as sediment and seawater of Moreton Bay where this sponge occurs. The characterization of these novel planctomycetes revealed that cells of one unique strain do not possess condensed nucleoids, a phenotype distinct from other planctomycetes. In addition, a culture-independent clone library approach identified unique planctomycete 16S rRNA gene sequences closely related to other sponge-derived sequences. The analysis of tissue of the sponge Niphates sp. showed that the mesohyl of the sponge is almost devoid of microbial cells, indicating this species is in the group of ‘low microbial abundant’ (LMA) sponges. The unique planctomycete 16S rRNA gene sequences identified in this study were phylogenetically closely related to sequences from LMA sponges in other published studies. This study has revealed new insights into the diversity of planctomycetes in the marine environment and the association of planctomycetes with marine sponges.     

Life-history differences among coral reef sponges promote mutualism or exploitation of mutualism by influencing partner fidelity feedback

Mutualism can be favored over exploitation of mutualism when interests of potential heterospecific partners are aligned so that individual organisms are beneficial to each others' continued growth, survival, and reproduction, that is, when exploitation of a particular partner individual is costly. A coral reef sponge system is particularly amenable to field experiments probing how costs of exploitation can be influenced by life-history characteristics. Pairwise associations among three of the sponge species are mutually beneficial. A fourth species, Desmapsamma anchorata, exploits these mutualisms. Desmapsamma also differs from the other species by growing faster, fragmenting more readily, and suffering higher mortality rates. Evaluating costs and benefits of association in the context of the complex life histories of these asexually fragmenting sponges shows costs of exploitation to be high for the mutualistic species but very low for this essentially weedy species. Although it benefits from association more than the mutualist species, by relying on their superior tensile strength and extensibility to reduce damage by physical disturbance, exploitation is favored because each individual host is of only ephemeral use. These sponges illustrate how life-history differences can influence the duration of association between individuals and, thus, the role of partner fidelity in promoting mutualism.     

Aquaculture of sponges on scallops for natural products research and antifouling

Suspended culture of scallops (Pectinidae: Bivalvia) is plagued by invertebrate fouling. Scallops covered in an orange sponge (Suberites ficus ssp. rubrus), however, do not have any other invertebrates fouling their shells and the sponge is easily removed. Sponges may also be valuable sources of bioactive compounds. Seven species of sponge were found to be associated with Chlamys opercularis but none were found associated with Pecten maximus. Standing crop of sponge on the scallop farm was just over one tonne. If all the scallops were covered by sponge this would rise to approximately 4.5 tonnes (from three million scallops). Primary cell cultures of (S.f. rubrus) were successfully established but no cell lines were achieved. A number of techniques were tried for establishing cells and pieces of sponge tissue onto scallop shells but none gave satisfactory results. Likewise mechanical methods for sticking small pieces of sponge to scallop shells were deemed impractical even where they resulted in subsequent sponge growth. Improving natural settlement of sponges onto the scallops was the only economically practical method for increasing sponge yield for C. opercularis, though other methods would need to be devised for P. maximus.     

Maerl grounds provide both refuge and high growth potential for juvenile queen scallops (Aequipecten opercularis L.)

Human damage to biogenic substrata such as maerl has been receiving increasing attention recently. Maerl forms highly biodiverse and heterogeneous habitats composed of loose-lying coralline red algae, which fulfil nursery area prerequisites for queen scallops (Aequipecten opercularis) and other invertebrates. The benefits obtained by queen scallops utilising maerl were poorly understood, so we used both laboratory predation and field tethering experiments to investigate the refuge and growth potential provided by pristine live maerl (PLM) grounds over other common substrata. In aquaria, more juvenile queen scallops (<35 mm shell height) survived on PLM than on gravel substrata in the presence of the crab Carcinus maenas or the starfish Asterias rubens. Field tethering experiments indicated similar survivorship of juvenile queen scallops on PLM than gravel; additionally, their growth rates were similar on both substrata. PLM allows scallops to seek refuge from predators and position themselves to optimise their food supply. Other bivalve refugia have been shown to provide poor food supply as a consequence of their high heterogeneity, yet maerl grounds provide a ‘win-win’ scallop nursery area coupling refuge availability with high food supply.     

Characterization of a Culturable Alphaproteobacterial Symbiont Common to Many Marine Sponges and Evidence for Vertical Transmission via Sponge Larvae

A closely related group of alphaproteobacteria were found to be present in seven genera of marine sponges from several locations and were shown to be transferred between sponge generations through the larvae in one of these sponges. Isolates of the alphaproteobacterium were cultured from the sponges Axinella corrugata, Mycale laxissima, Monanchora unguifera, and Niphates digitalis from Key Largo, Florida; Didiscus oxeata and Monanchora unguifera from Discovery Bay, Jamaica; an Acanthostronglyophora sp. from Manado, Indonesia; and Microciona prolifera from the Cheasapeake Bay in Maryland. Isolates were very similar to each other on the basis of 16S rRNA gene sequence (>99% identity) and are closely related to Pseudovibrio denitrificans. The bacterium was never isolated from surrounding water samples and was cultured from larvae of M. laxissima, indicating that it is a vertically transmitted symbiont in this sponge. Denaturing gradient gel electrophoresis, 16S rRNA gene clone library analysis, and fluorescent in situ hybridization with probes specific to the alphaproteobacterium confirmed the presence of this bacterium in the M. laxissima larvae. The alphaproteobacterium was densely associated with the larvae rather than being evenly distributed throughout the mesohyl. This is the first report of the successful culture of a bacterial symbiont of a sponge that is transferred through the gametes.     

Analysis of bacterial communities in sponges and coral inhabiting Red Sea,using barcoded 454 pyrosequencing

Microbial communities are linked with marine sponge are diverse in their structure and function. Our understanding of the sponge-associated microbial diversity is limited especially from Red Sea in Saudi Arabia where few species of sponges have been studied. Here we used pyrosequencing to study two marine sponges and coral species sampled from Obhur region from Red sea in Jeddah. A total of 168 operational taxonomic units (OTUs) were identified from Haliclona caerulea, Stylissa carteri and Rhytisma fulvum. Taxonomic identification of tag sequences of 16S ribosomal RNA revealed 6 different bacterial phyla and 9 different classes. A proportion of unclassified reads were was also observed in sponges and coral sample. We found diverse bacterial communities associated with two sponges and a coral sample. Diversity and richness estimates based on OUTs revealed that sponge H. caerulea had significantly high bacterial diversity. The identified OTUs showed unique clustering in three sponge samples as revealed by Principal coordinate analysis (PCoA). Proteobacteria (88–95%) was dominant phyla alonwith Bacteroidetes, Planctomycetes, Cyanobacteria, Firmicutes and Nitrospirae. Seventeen different genera were identified where genus Pseudoalteromonas was dominant in all three samples. This is first study to assess bacterial communities of sponge and coral sample that have never been studied before to unravel their microbial communities using 454-pyrosequencing method.     

Domestication reduces the capacity to escape from predators

Phenotypic plasticity in response to variations in predatory pressure frequently occurs in wild populations, but it may be more evident and critical in species subjected to high exploitation rates and aquaculture. The Chilean scallop Argopecten purpuratus is becoming a domesticated species and the production of hatchery-reared scallops (closed environment), has implied the development of successive generations of individuals deprived of several stimuli normally present in their natural habitats (e.g. predators). We compared the escape capacities between wild and cultured A. purpuratus and also evaluated the effect of reproductive investment on the escape response capacities. Wild and cultured scallops, at different reproductive stages (maturing, mature and spawned), were stimulated to escape with the predatory sea star Meyenaster gelatinosus. We recorded: (1) the time to reaction, (2) the total number of claps, the duration of the clapping response and the clapping rate until exhaustion, (3) the time they spent closed after exhaustion, and (4) the proportion of claps recovered, the duration of the clapping response and the clapping rate after 20 min of recuperation. We found that wild A. purpuratus (1) reacted earlier when contacted by their natural predator, (2) escaped faster (greater clapping rates), (3) spent less time with their valves closed when exhausted, and (4) most of their escape capacities (i.e. claps number; clapping time; capacity of recuperation) were less affected by the energetic requirements imposed by gonad maturation and/or spawning than in cultured scallops. We considered that all these aspects of the escape response would make wild scallops less vulnerable to predation than cultured scallops, thus decreasing predation risk. Given the reduction of escape performance in cultured scallops, we suggest that this aspect should be considered for the success of culture-based restocking programs.     

Unusual Symbiotic Cyanobacteria Association in the Genetically Diverse Intertidal Marine Sponge Hymeniacidon perlevis (Demospongiae,Halichondrida)

Cyanobacteria represent one of the most common members of the sponge-associated bacterial community and are abundant symbionts of coral reef ecosystems. In this study we used Transmission Electron Microscopy (TEM) and molecular techniques (16S rRNA gene marker) to characterize the spatial distribution of cyanobionts in the widely dispersed marine intertidal sponge Hymeniacidon perlevis along the coast of Portugal (Atlantic Ocean). We described new sponge associated cyanobacterial morphotypes (Xenococcus-like) and we further observed Acaryochloris sp. as a sponge symbiont, previously only reported in association with ascidians. Besides these two unique cyanobacteria, H. perlevis predominantly harbored Synechococcus sp. and uncultured marine cyanobacteria. Our study supports the hypothesis that the community of sponge cyanobionts varies irrespective of the geographical location and is likely influenced by seasonal fluctuations. The observed multiple cyanobacterial association among sponges of the same host species over a large distance may be attributed to horizontal transfer of symbionts. This may explain the absence of a co-evolutionary pattern between the sponge host and its symbionts. Finally, in spite of the short geographic sampling distance covered, we observed an unexpected high intra-specific genetic diversity in H. perlevis using the mitochondrial genes ATP6 (π = 0.00177), COI (π = 0.00241) and intergenic spacer SP1 (π = 0.00277) relative to the levels of genetic variation of marine sponges elsewhere. Our study suggests that genotypic variation among the sponge host H. perlevis and the associated symbiotic cyanobacteria diversity may be larger than previously recognized.     

Metagenomic Analysis of Genes Encoding Nutrient Cycling Pathways in the Microbiota of Deep-Sea and Shallow-Water Sponges

Sponges host complex symbiotic communities, but to date, the whole picture of the metabolic potential of sponge microbiota remains unclear, particularly the difference between the shallow-water and deep-sea sponge holobionts. In this study, two completely different sponges, shallow-water sponge Theonella swinhoei from the South China Sea and deep-sea sponge Neamphius huxleyi from the Indian Ocean, were selected to compare their whole symbiotic communities and metabolic potential, particularly in element transformation. Phylogenetically diverse bacteria, archaea, fungi, and algae were detected in both shallow-water sponge T. swinhoei and deep-sea sponge N. huxleyi, and different microbial community structures were indicated between these two sponges. Metagenome-based gene abundance analysis indicated that, though the two sponge microbiota have similar core functions, they showed different potential strategies in detailed metabolic processes, e.g., in the transformation and utilization of carbon, nitrogen, phosphorus, and sulfur by corresponding microbial symbionts. This study provides insight into the putative metabolic potentials of the microbiota associated with the shallow-water and deep-sea sponges at the whole community level, extending our knowledge of the sponge microbiota’s functions, the association of sponge- microbes, as well as the adaption of sponge microbiota to the marine environment.     

Pyrosequencing reveals highly diverse and species-specific microbial communities in sponges from the Red Sea

Marine sponges are associated with a remarkable array of microorganisms. Using a tag pyrosequencing technology, this study was the first to investigate in depth the microbial communities associated with three Red Sea sponges, Hyrtios erectus, Stylissa carteri and Xestospongia testudinaria. We revealed highly diverse sponge-associated bacterial communities with up to 1000 microbial operational taxonomic units (OTUs) and richness estimates of up to 2000 species. Altogether, 26 bacterial phyla were detected from the Red Sea sponges, 11 of which were absent from the surrounding sea water and 4 were recorded in sponges for the first time. Up to 100 OTUs with richness estimates of up to 300 archaeal species were revealed from a single sponge species. This is by far the highest archaeal diversity ever recorded for sponges. A non-negligible proportion of unclassified reads was observed in sponges. Our results demonstrated that the sponge-associated microbial communities remained highly consistent in the same sponge species from different locations, although they varied at different degrees among different sponge species. A significant proportion of the tag sequences from the sponges could be assigned to one of the sponge-specific clusters previously defined. In addition, the sponge-associated microbial communities were consistently divergent from those present in the surrounding sea water. Our results suggest that the Red Sea sponges possess highly sponge-specific or even sponge-species-specific microbial communities that are resistant to environmental disturbance, and much of their microbial diversity remains to be explored.     

Nitrogen Biogeochemistry in the Caribbean Sponge,Xestospongia muta: A Source or Sink of Dissolved Inorganic Nitrogen?

Background

Sponges have long been known to be ecologically important members of the benthic fauna on coral reefs. Recently, it has been shown that sponges are also important contributors to the nitrogen biogeochemistry of coral reefs. The studies that have been done show that most sponges are net sources of dissolved inorganic nitrogen (DIN; NH₄ ⁺ and NO₃ ⁻) and that nitrification, mediated by their symbiotic prokaryotes, is the primary process involved in supplying DIN to adjacent reefs.

Methodology/Principal Findings

A natural experiment was conducted with the Caribbean sponge Xestospongia muta from three different locations (Florida Keys, USA; Lee Stocking Island, Bahamas and Little Cayman, Cayman Islands). The DIN fluxes of sponges were studied using nutrient analysis, stable isotope ratios, and isotope tracer experiments. Results showed that the fluxes of DIN were variable between locations and that X. muta can be either a source or sink of DIN. Stable isotope values of sponge and symbiotic bacterial fractions indicate that the prokaryotic community is capable of taking up both NH₄ ⁺ and NO₃ ⁻ while the differences in δ ¹⁵N between the sponge and bacterial fractions from the NH₄ ⁺ tracer experiment suggest that there is translocation of labeled N from the symbiotic bacteria to the host.

Conclusions/Significance

Nitrogen cycling in X. muta appears to be more complex than previous studies have shown and our results suggest that anaerobic processes such as denitrification or anammox occur in these sponges in addition to aerobic nitrification. Furthermore, the metabolism of this sponge and its prokaryotic symbionts may have a significant impact on the nitrogen biogeochemistry on Caribbean coral reefs by releasing large amounts of DIN, including higher NH₄ ⁺ concentrations that previously reported.     

Composition of Archaea in Seawater,Sediment, and Sponges in the Kepulauan Seribu Reef System,Indonesia

Coral reefs are among the most diverse and productive ecosystems in the world. Most research has, however, focused on eukaryotes such as corals and fishes. Recently, there has been increasing interest in the composition of prokaryotes, particularly those inhabiting corals and sponges, but these have mainly focused on bacteria. There have been very few studies of coral reef Archaea, despite the fact that Archaea have been shown to play crucial roles in nutrient dynamics, including nitrification and methanogenesis, of oligotrophic environments such as coral reefs. Here, we present the first study to assess Archaea in four different coral reef biotopes (seawater, sediment, and two sponge species, Stylissa massa and Xestospongia testudinaria). The archaeal community of both sponge species and sediment was dominated by Crenarchaeota, while the seawater community was dominated by Euryarchaeota. The biotope explained more than 72 % of the variation in archaeal composition. The number of operational taxonomic units (OTUs) was highest in sediment and seawater biotopes and substantially lower in both sponge hosts. No “sponge-specific” archaeal OTUs were found, i.e., OTUs found in both sponge species but absent from nonhost biotopes. Despite both sponge species hosting phylogenetically distinct microbial assemblages, there were only minor differences in Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathways. In contrast, most functional pathways differed significantly between microbiomes from sponges and nonhost biotopes including all energy metabolic pathways. With the exception of the methane and nitrogen metabolic pathway, all energy metabolic pathways were enriched in sponges when compared to nonhost biotopes.