Eutrophication has no short-term effect on the Cymbastela stipitata holobiont

Levels of nitrogen in coastal areas have been rapidly increasing due to accumulative inputs of sewage and terrigenous sediments carrying fertilizers. Sponges have an immense filtering capacity and may be directly impacted (positively or negatively) by elevated concentrations of nitrogen. Sponges also host a wide diversity of microbes involved in nitrogen metabolism, yet little is known about the effects of nitrogen loading on these symbiotic partnerships. Manipulative experiments were undertaken to examine the potential effects of excess nitrogen (up to 240 μM) on microbial symbiosis in the abundant sponge species Cymbastela stipitata. Microbial composition and activity were examined using 454-pyrotag sequencing of DNA- and RNA-derived samples. Despite the high levels of nitrogen exposure (up to 124-fold above ambient), sponges appeared visibly unaffected at all treatment concentrations. At the phylum level, the microbial community was consistent between all sponge samples regardless of nitrogen treatment, with Cyanobacteria and Thaumarchaeota being the dominant taxa. Higher microbial diversity was observed at the operational taxonomic units (OTU) level (97% sequence similarity), with only 40% of OTUs shared between samples from all treatments. However, a single cyanobacterial OTU dominated the community of all individuals (average 73.5%) and this OTU did not vary with nitrogen treatment. The conserved microbial community in all sponges irrespective of nitrogen treatment highlights the stability of the sponge-microbe relationship and indicates that the holobiont is resistant to short pulses of nitrogen at levels mimicking sewage effluent

Biogeographic variation in the microbiome of the ecologically important sponge, Carteriospongia foliascens

Sponges are well known for hosting dense and diverse microbial communities, but how these associations vary with biogeography and environment is less clear. Here we compared the microbiome of an ecologically important sponge species, Carteriospongia foliascens, over a large geographic area and identified environmental factors likely responsible for driving microbial community differences between inshore and offshore locations using co-occurrence networks (NWs). The microbiome of C. foliascens exhibited exceptionally high microbial richness, with more than 9,000 OTUs identified at 97% sequence similarity. A large biogeographic signal was evident at the OTU level despite similar phyla level diversity being observed across all geographic locations. The C. foliascens bacterial community was primarily comprised of Gammaproteobacteria (34.2% ± 3.4%) and Cyanobacteria (32.2% ± 3.5%), with lower abundances of Alphaproteobacteria, Bacteroidetes, unidentified Proteobacteria, Actinobacteria, Acidobacteria and Deltaproteobacteria. Co-occurrence NWs revealed a consistent increase in the proportion of Cyanobacteria over Bacteroidetes between turbid inshore and oligotrophic offshore locations, suggesting that the specialist microbiome of C. foliascens is driven by environmental factors

Climate change alterations to ecosystem dominance: how might sponge-dominated reefs function?

Anthropogenic stressors are impacting ecological systems across the world. Of particular concern are the recent rapid changes occurring in coral reef systems. With ongoing degradation from both local and global stressors, future reefs are likely to function differently to current coral-dominated ecosystems. Determining key attributes of future reef states is critical to reliably predict outcomes for ecosystem service provision. Here we explore the impacts of changing sponge dominance on coral reefs. Qualitative modelling of reef futures suggests that changing sponge dominance due to increased sponge abundance will have different outcomes for other trophic levels compared with increased sponge dominance as a result of declining coral abundance. By exploring uncertainty in the model outcomes we identify the need to: i) quantify changes in carbon flow through sponges, ii) determine the importance of food limitation for sponges, iii) assess the ubiquity of the recently described 'sponge loop', iv) determine the competitive relationships between sponges and other benthic taxa, particularly algae, and v) understand how changing dominance of other organisms alters trophic pathways and energy flows through ecosystems. Addressing these knowledge gaps will facilitate development of more complex models that assess functional attributes of sponge-dominated reef ecosystems. This article is protected by copyright. All rights reserved

Thermal and Sedimentation Stress Are Unlikely Causes of Brown Spot Syndrome in the Coral Reef Sponge, Ianthella basta

Background: Marine diseases are being increasingly linked to anthropogenic factors including global and local stressors. On the Great Barrier Reef, up to 66% of the Ianthella basta population was recently found to be afflicted by a syndrome characterized by brown spot lesions and necrotic tissue.\ud \ud Methodology/Principal Findings: Manipulative experiments were undertaken to ascertain the role of environmental stressors in this syndrome. Specifically, the effects of elevated temperature and sedimentation on sponge health and symbiont stability in I. basta were examined. Neither elevated temperature nor increased sedimentation were responsible for the brown spot lesions, but sponges exposed to 32°C developed substantial discoloration and deterioration of their tissues, resulting in death after eight days and a higher microbial diversity in those samples. No shifts in the microbial community of I. basta were observed across a latitudinal gradient or with increased sedimentation, with three previously described symbionts dominating the community of all sponges (Alphaproteobacteria, Gammaproteobacteria and Thaumarchaea).\ud \ud Conclusions/Significance: Results from this study highlight the stable microbial community of I. basta and indicate that thermal and sedimentation stress are not responsible for the brown spot lesions currently affecting this abundant and ecologically important sponge species

The effects of disease and stress on the microbial community of the sponge Ianthella basta

Sponges form a highly diverse and ecologically significant component of benthic communities. Despite their ecological importance, threats to populations and communities, including disease dynamics in sponges, remain relatively unexplored. There have been severe disease epidemics in sponges from the Caribbean and the Mediterranean; however, evidence of extensive sponge mortalities have not been reported in the Great Barrier Reef (GBR) or Torres Strait, northeastern Australia. This thesis describes a disease-like syndrome affecting the sponge Ianthella basta, a sponge that is common to both regions. The prevalence of disease as well as a comprehensive analysis of the microbial communities associated with affected and healthy sponges was determined. Manipulation of environmental parameters, including temperature and sedimentation were undertaken to establish potential causes of the disease-like syndrome. In addition, the microbial community associated with tissue regression of I. basta is also reported.\ud \ud Disease prevalence surveys were conducted in the Palm Islands on the central GBR and Masig Island, Torres Strait. Symptoms of the disease-like syndrome affecting I. basta included discolored, necrotic spots leading to tissue degradation, exposure of the skeletal fibers and disruption of the choanocyte chambers. Sponges were assigned to pre-determined disease categories using tissue necrosis and the presence of brown spot lesions as a proxy of health. Sponges with brown spot lesions were present at all sites with 43% and 66% of I. basta exhibiting disease-like symptoms in the Palm Islands and Torres Strait, respectively. Sponges from Torres Strait also showed a greater incidence of significant and extensive necrosis in comparison to sponges from Palm Island (11.5 vs. 6%).\ud \ud A comprehensive comparison of bacteria, viruses, fungi and other eukaryotes was performed in healthy and diseased I. basta using multiple techniques to ascertain the role of microbes in the disease process. A low diversity of microbes was observed in both healthy and diseased sponge communities, with all sponges dominated by an Alphaproteobacteria, a Gammaproteobacteria and a Thaumarchaea. Bacterial cultivation, community analysis by Denaturing Gradient Gel Electrophoresis (DGGE) (Bacteria and Eukarya), sequencing of 16S rRNA clone libraries (Bacteria and Archaea) and direct visual assessment by electron microscopy failed to reveal any putative pathogens. In addition, infection assays could not establish the syndrome in healthy sponges even after direct physical contact with affected tissue. These results suggest that microbes are not responsible for the formation of brown spot lesions and necrosis in I. basta.\ud \ud Elevated temperatures and other anthropogenic factors are increasingly being linked with disease in marine organisms. Manipulative experiments were undertaken to ascertain the potential role of environmental stressors (temperature and sedimentation) in the formation of brown spot lesions and necrosis in I. basta. In addition, the effects of elevated temperature, sedimentation and antibiotic exposure on the microbial community of I. basta were quantified. Neither elevated temperatures nor increased sedimentation induced the formation of brown spot lesions, indicating they are not responsible for the syndrome. However, sponges exposed to 32˚C developed substantial discoloration and deterioration of their tissues, resulting in death after eight days. The decline in sponge heath was accompanied by a shift in the microbial community, with higher diversity observed within the Alpha- and Gammaproteobacteria. Though this shift occurred, the microbial community was stable in sponges exposed to this temperature (32˚C) for the first four days of the experiment. No shifts in the microbial community of I. basta were observed with increased sedimentation and antibiotic exposure, with all dominant symbionts present (Alphaproteobacteria, Gammaproteobacteria and Thaumarchaea). Overall, these results indicate I. basta has a stable microbial community.\ud \ud The physiological stress response of tissue regression observed in heat-stressed I. basta was further explored. Following collection and transportation, tissues of I. basta often regress leaving visible subdermal gaps between primary fibers. Changes in the bacterial communities associated with each tissue state were also assessed using DGGE. Six necrotic specimens of I. basta and 12 healthy sponge explants were collected at Orpheus Is., northeastern Australia and transported to aquarium facilities at the Australian Institute of Marine Science. After 12 h both the healthy explants and necrotic sponges displayed substantial tissue contraction with visible gaps evident between sponge skeletal fibers. However, within 72 h all sponges recovered to their original states. To quantify the level of tissue regression and subsequent recovery, a photo of each sponge was taken and images were compared using an integrated density measurement of Image Tool for Windows (UTHSCA). Histological samples were taken from sponge explants to compare cellular organization during this regression and recovery process. The integrated density of the sponge tissue effectively doubled within 72 h (increasing by 92%), confirming tissue recovery in I. basta. Histological analysis of the explants revealed that sponges affected by tissue regression had significantly fewer choanocyte chambers [(0.4 ± 0.1 vs. 4.5 ± 0.7) (mean ± S.E)] in regressed and recovered tissues respectively, and more densely packed granulated cells than recovered sponges. Principal Component Analysis of the DGGE data showed consistent patterns of microbial symbionts in both regressed and recovered sponges.\ud \ud This thesis represents a systematic approach to investigating disease in sponges, which can be used as a template for future research. Results obtained in this thesis contribute valuable baseline data on a disease-like syndrome affecting a common marine sponge and provide evidence that microorganisms are unlikely the causative agent. In addition, disease-like symptoms were never induced in response to temperature or sedimentation stress, indicating an environmental origin of the syndrome is also unlikely

Influence of size and spatial competition on the bioactivity of coral reef sponges

Sponges biosynthesize a wealth of secondary metabolites, many with novel structures and strong biological activity. Such compounds may serve multiple ecological roles including anti-predation, anti-fouling functionalities and are implicated in border defense or attack during spatial competition. Relative size of benthic organisms may also play an important role in competitive interactions. To determine if a relationship exists between individual size and bioactive metabolite production in the context of spatial competition, we examined three sponge species with different morphologies: the massive Coscinoderma matthewsi, the club-shaped branching Hyrtios erecta, and the fan-shaped Ianthella basta. Extracts from sponges of various sizes and competitive environments were examined using a cell based bioassay as a proxy of bioactivity. For I. basta, sponge size was correlated with bioactivity; the largest individuals generally being the most bioactive. In contrast, there was no correlation between size and bioactivity for either C. matthewsi or H. erecta. Bioactivity of sponges in this study were however highly variable among individuals, regardless of levels of competition. The prevalence of encroaching organisms was not correlated with sponge size for any of the three sponge species, suggesting that potential bioactivity is not influenced by surrounding competition

Cryptic speciation and phylogeographic relationships in the elephant ear sponge Ianthella basta (Porifera, Ianthellidae) from northern Australia

Morphological delineation of sponge species is hindered by the narrow range of fixed diagnostic characters and our limited knowledge of how much phenotypic plasticity the sponge body plan assumes in response to environmental conditions. Here, we make use of the partial mitochondrial cytochrome c oxidase subunit I (COI) gene and the second internal transcribed spacer (ITS2) region to assess the taxonomic validity of colour morphotypes observed in the elephant ear sponge Ianthella basta (Pallas, 1776) across its distribution range in northern Australia, and explore levels and patterns of genetic diversity among populations of the species collected from both sides of the Torres Strait. Molecular phylogenetic analyses revealed congruent topologies consistent with three evolutionarily significant units (ESUs) that were independent of the morphology of the sponge. ESU I includes previously morphologically and genetically delineated western Pacific specimens of I. basta (Guam), and probably corresponds to the type specimen originally described from Indonesia. ESU I occurs in almost all sampling sites across northern Australia, suggesting considerable levels of connectivity among reefs throughout the Torres Strait. ESUs II and III are each exclusively associated with a geographic region of high sponge species richness separated by Torres Strait, and probably represent the result of historical population fragmentation

Cytotoxic and anti-microbial activity of the sponge Iotrochota sp. as a function of size and spatial competitors

Secondary metabolites from marine invertebrates, such as sponges, have diverse ecological roles and may be used in anti-predation, anti-fouling and spatial competition. The thin encrusting sponge Iotrochota sp., found on the Great Barrier Reef, Australia, contains several novel indoles that may aid in spatial competition. To examine whether levels of surrounding competition affect the toxicity of Iotrochota sp., 24 sponges from Salamander Reef, Central Great Barrier Reef, subject to either high or low levels of surrounding competition, were sampled. Tissue samples were taken from areas where the sponge was in direct competition with neighbouring sessile invertebrates, as well as from areas where competition was less obvious. Compounds from the tissue samples were extracted and tested in both cytotoxicity and anti-microbial assays. However, neither cytotoxicity nor anti-microbial activity varied significantly between the high and low competition treatments. Cytotoxicity was greatest among large sponges, suggesting that size is an important factor contributing to the toxicity of Iotrochota sp. sponges in this study

Exploring the Role of Microorganisms in the Disease-Like Syndrome Affecting the Sponge Ianthella basta▿ †

A disease-like syndrome is currently affecting a large percentage of the Ianthella basta populations from the Great Barrier Reef and central Torres Strait. Symptoms of the syndrome include discolored, necrotic spots leading to tissue degradation, exposure of the skeletal fibers, and disruption of the choanocyte chambers. To ascertain the role of microbes in the disease process, a comprehensive comparison of bacteria, viruses, fungi, and other eukaryotes was performed in healthy and diseased sponges using multiple techniques. A low diversity of microbes was observed in both healthy and diseased sponge communities, with all sponges dominated by an Alphaproteobacteria, a Gammaproteobacteria, and a group I crenarchaeota. Bacterial cultivation, community analysis by denaturing gradient gel electrophoresis (Bacteria and Eukarya), sequencing of 16S rRNA clone libraries (Bacteria and Archaea), and direct visual assessment by electron microscopy failed to reveal any putative pathogens. In addition, infection assays could not establish the syndrome in healthy sponges even after direct physical contact with affected tissue. These results suggest that microbes are not responsible for the formation of brown spot lesions and necrosis in I. basta

Same, same but different: symbiotic bacterial associations in GBR sponges

Symbioses in marine sponges involve diverse consortia of microorganisms that contribute to the health and ecology of their hosts. The microbial communities of 13 taxonomically diverse Great Barrier Reef (GBR) sponge species were assessed by DGGE and 16S rRNA gene sequencing to determine intra and inter species variation in bacterial symbiont composition. Microbial profiling revealed communities that were largely conserved within different individuals of each species with intra species similarity ranging from 65–100%. 16S rRNA gene sequencing revealed that the communities were dominated by Proteobacteria, Chloroflexi, Acidobacteria, Actinobacteria, Nitrospira, and Cyanobacteria. Sponge-associated microbes were also highly host-specific with no operational taxonomic units (OTUs) common to all species and the most ubiquitous OTU found in only 5 of the 13 sponge species. In total, 91% of the OTUs were restricted to a single sponge species. However, GBR sponge microbes were more closely related to other sponge-derived bacteria than they were to environmental communities with sequences falling within 50 of the 173 previously defined sponge-(or sponge-coral) specific sequence clusters (SC). These SC spanned the Acidobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Gemmatimonadetes, Nitrospira, and the Planctomycetes-Verrucomicrobia-Chlamydiae superphylum. The number of sequences assigned to these sponge-specific clusters across all species ranged from 0 to 92%. No relationship between host phylogeny and symbiont communities were observed across the different sponge orders, although the highest level of similarity was detected in two closely related Xestospongia species. This study identifies the core microbial inhabitants in a range of GBR sponges thereby providing the basis for future studies on sponge symbiotic function and research aiming to predict how sponge holobionts will respond to environmental perturbation