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

Characterization of bacterial communities associated with the tyrian purple producing gland in a marine gastropod

Dicathais orbita is a marine mollusc recognised for the production of anticancer compounds that are precursors to Tyrian purple. This study aimed to assess the diversity and identity of bacteria associated with the Tyrian purple producing hypobranchial gland, in comparison with foot tissue, using a high-throughput sequencing approach. Taxonomic and phylogenetic analysis of variable region V1-V3 of 16S rRNA bacterial gene amplicons in QIIME and MEGAN were carried out. This analysis revealed a highly diverse bacterial assemblage associated with the hypobranchial gland and foot tissues of D. orbita. The dominant bacterial phylum in the 16S rRNA bacterial profiling data set was Proteobacteria followed by Bacteroidetes, Tenericutes and Spirochaetes. In comparison to the foot, the hypobranchial gland had significantly lower bacterial diversity and a different community composition, based on taxonomic assignment at the genus level. A higher abundance of indole producing Vibrio spp. and the presence of bacteria with brominating capabilities in the hypobranchial gland suggest bacteria have a potential role in biosynthesis of Tyrian purple in D. orbita

Closing the lifecycle for the sustainable aquaculture of the bath sponge Coscinoderma matthewsi

Aquaculture of the bath sponge Coscinoderma matthewsi relies on collection of seed stock from the wild. This study investigated the potential of larval culture as a sustainable source of seed stock by quantifying reproduction, larval metamorphosis, and juvenile survival and growth of C. matthewsi. The accuracy of using surface area (2-dimensional) measurements as a proxy for juvenile growth was also assessed against volumetric (3-dimensional) data. Coscinoderma matthewsi is gonochoric and releases parenchymellae larvae over several weeks, corresponding with increasing sea surface temperatures, over the Austral summer (26.6 °C in November and 29.1 °C in January). Sexual maturity is size dependent and smaller individuals (1267.78 cm3 ± 405.66) were non-reproductive. There were no size differences between males and females and both sexes occur in equal proportions. Male reproductive output (ROI) (4.33% ± 0.75) was higher than females (1.62% ± 0.15). Larval metamorphic success was 98.0% ± 2 after 72 h post-release. Juvenile survival over seven months was independent of settlement density and ranged between 18% and 30%. Using surface area underestimated growth of juvenile sponges by approximately half in comparison to volume estimates. This study demonstrates larval culture as a sustainable source of seed stock to support large scale aquaculture operations

Larval vertical migration and hierarchical selectivity of settlement in a brooding marine sponge

Knowledge of larval behaviours of sessile marine invertebrates from release to recruitment and of the role these behaviours play in determining adult distributions is limited. In manipulative experiments using larvae from the Great Barrier Reef sponge Rhopaloeides odorabile, we quantified larval behaviours associated with vertical migration, phototaxis and swimming ability. We also measured settlement responses to cues associated with light, settlement surface micro-topography, coral rubble and biofilms. Following an afternoon release, the majority of larvae (72%) migrated vertically to the surface (light) for 6 to 18 h. After 24 h, 55% of active larvae had moved from the surface to the bottom and maintained this position for up to 54 h before settling. Larvae did not display gregarious settlement patterns, or a preference for settlement surface topographies, but did preferentially settle to light-exposed surfaces. Initial settlement to biofilms or coral rubble was higher than in controls with no cue. However, the transition from initial settlement and attachment to metamorphosis was much higher when treatments comprised a combination of biofilm and coral rubble compared to biofilm-only treatments (49 vs. 9%). Overall, this demonstrates that hierarchical cues contribute to selective settlement. Vertical migration to surface waters facilitates passive dispersal via wind-driven surface currents and contributes to wide-scale dispersal, while a subsequent demersal phase, where larvae actively explore the benthos for settlement sites, enables dispersal over fine, micro-geographic spatial scales

A hierarchy of settlement cues influences larval behaviour in a coral reef sponge

For sessile marine invertebrates, processes contributing to larval release, dispersal, and settlement in favourable habitats are central to patterns of distribution and community structure. We quantified larval release patterns, phototactic behaviour, and settlement in response to environmental cues for the coral reef sponge Luffariella variabilis. Individual sponges released up to 830 larvae d–1. Larvae displayed phototactic behaviours by swimming upwards after release for brief periods (40 min), after which time most larvae (\u3e95%) exhibited negative phototaxis. Light played a role in determining numbers and rates of larval settlement. Light levels of 56 µmol s–1 m–2 reduced the rate of settlement and inhibited larval settlement by 60% compared to dark controls. However, at lower light levels (0.7 to 0.34 µmol s–1 m–2), both time to settlement and numbers of larvae settling were consistent with settlement in dark controls. Larval settlement increased in the presence of other larvae, with \u3e95% of larvae settling when placed in treatments with 50 individuals, compared to 50% settlement for treatments containing only 1 individual. The gregarious settlement of L. variabilis larvae was associated with conspecific larval settlement cues. Settlement in ‘conditioned’ water from which 200 larvae had previously settled and subsequently been removed was 80%, compared to 20% in controls. Our study unequivocally demonstrates that a conspecific cue not related to adults or other biotic or abiotic factors induces settlement in larvae. Our observations, the preference of larvae to settle in response to low light levels and of settlement increased by gregariousness, correspond with the cryptic and clumped distribution of L. variabilis in the field

Combining morphometrics with molecular taxonomy: how different are similar foliose keratose sponges from the Australian tropics?

Sponge taxonomy can be challenging as many groups exhibit extreme morphological plasticity induced by local environmental conditions. Foliose keratose sponges of the sub-family Phyllospongiinae (Dictyoceratida, Thorectidae: Strepsichordaia,Phyllospongia and Carteriospongia) are commonly found in intertidal and subtidal habitats of the Indo-Pacific. Lacking spicules, these sponges can be difficult to differentiate due to the lack of reliable morphological characters for species delineation. We use molecular phylogenies inferred from the nuclear Internal Transcribed Spacer 2 region (ITS2) and morphometrics (19 characters; 52 character states) to identify evolutionarily significant units (ESUs; sensu Moritz) within foliose Phyllosponginiids collected from seven geographic locations across tropical eastern and Western Australia. The ITS2 topology was congruent with the tree derived from Bayesian inference of discrete morphological characters supporting expected taxonomic relationships at the genus level and the identification of five ESUs. However, phylogenies inferred from the ITS2 marker revealed multiple sequence clusters, some of which were characterised by distinct morphological features and specific geographic ranges. Our results are discussed in light of taxonomic incongruences within this study, hidden sponge diversity and the role of vicariant events in influencing present day distribution patterns

An assessment of the aquaculture potential of the tropical sponges Rhopaloeides odorabile and Coscinoderma sp.

Sponge aquaculture offers the opportunity to provide a sustainable supply of bath and industrial sponges and mitigate the environmental effects of over-harvesting. The potential to develop sponge aquaculture is diverse given the variety of sponge species. However, amenability to culture and the selection of appropriate culture methods are species specific and need to be determined to provide the platform for commercial success. In this study the survival (in situ and ex situ), growth rates (in situ), and recovery processes (ex situ) were measured for explants of two sponge aquaculture candidates, Rhopaloeides odorabile Thompson et al. and Coscinoderma sp. [Phylum Porifera: Order Dictyoceratida: Family Spongiidae], cultured in the Palm Islands Group of the central Great Barrier Reef. Sponge survival was dependent on the species, experiment duration, and method of culture. For both species the highest mortality occurred within days of excision of sponge material from parent stock, and mortalities were negligible after 78 days. After 78 days, R. odorabile had highest survival ex situ (75%) and lowest in situ (60%). In contrast, Coscinoderma sp. had the lowest survival ex situ (30%) and highest in situ (90%). The total growth of R. odorabile (146.0 ± 40.3%) and Coscinoderma sp. (195.9 ± 39.8%) was not significantly different over the 21 month experimental period, but was highly variable between explants from the same individual. Both species demonstrated initial size dependent growth rates with smaller explants growing fastest over the first 78 days. Explant recovery rates were rapid for both species with a protective layer of collagen forming over the surface within 24 h. This layer was replaced by pinacoderm between 3 and 41 days after excision as the subsurface tissue reorganised to recreate a functional surface for each species, including redevelopment of the aquiferous system within 41 days for R. odorabile. R. odorabile and Coscinoderma sp. both show potential for commercial aquaculture, however, further research is required to reduce initial mortality rates and the high variability in growth rates between explants

Spatial variability in community structure of Dictyoceratida sponges across Torres Strait, Australia

Spatial variability in community structure of dictyoceratid sponges (class Demospongiae; order Dictyoceratida) was examined on coral reefs in Torres Strait, an archipelago of islands and reefs between northern Queensland, Australia, and Papua New Guinea. Dictyoceratid sponge abundances and environmental factors were recorded at four locations, separated by 50–220 km. Each location was subdivided into 5–7 sites, each ⩾2 km apart. At each site, four 50×2 m belt transects were quantitatively surveyed, recording the dictyoceratid numbers, substrate type (rock, rubble and sand), water clarity, degree of reef slope and depth. Dictyoceratid abundance was similar among locations over large spatial scales, averaging 15.5 individuals per 100 m2, but varied significantly among sites within particular locations (i.e. small scale heterogeneity). Twenty-three dictyoceratid species were recorded in Torres Strait, with approximately half (12/23) found in only one location. The canonical correspondence analysis determined that the measured environmental factors explained only 26% of the spatial variation. Cluster analysis revealed a complex dictyoceratid community structure with similarities among neighbouring sites and among sites separated by hundreds of kilometres. Conversely the abundance and composition of dictyoceratids could vary greatly between neighbouring sites 2 km apart and on the same reef complex. The results of this study suggest that spatial variability of dictyoceratid sponges in Torres Strait is influenced by a combination of environmental, biological and stochastic processes

A decadal analysis of bioeroding sponge cover on the inshore Great Barrier Reef

Decreasing coral cover on the Great Barrier Reef (GBR) may provide opportunities for rapid growth and expansion of other taxa. The bioeroding sponges Cliona spp. are strong competitors for space and may take advantage of coral bleaching, damage, and mortality. Benthic surveys of the inshore GBR (2005–2014) revealed that the percent cover of the most abundant bioeroding sponge species, Cliona orientalis, has not increased. However, considerable variation in C. orientalis cover, and change in cover over time, was evident between survey locations. We assessed whether biotic or environmental characteristics were associated with variation in C. orientalis distribution and abundance. The proportion of fine particles in the sediments was negatively associated with the presence-absence and the percent cover of C. orientalis, indicating that the sponge requires exposed habitat. The cover of corals and other sponges explained little variation in C. orientalis cover or distribution. The fastest increases in C. orientalis cover coincided with the lowest macroalgal cover and chlorophyll a concentration, highlighting the importance of macroalgal competition and local environmental conditions for this bioeroding sponge. Given the observed distribution and habitat preferences of C. orientalis, bioeroding sponges likely represent site-specific – rather than regional – threats to corals and reef accretion

Patterns of reproduction in two co-occurring Great Barrier Reef sponges

Reproduction is a key biological process that underpins the persistence and maintenance of populations. However, information on the reproductive biology of Great Barrier Reef (GBR) sponges is depauperate. The present study established the reproductive biology of two co-occurring GBR sponges, namely Ianthella basta (Verongida) and Ircinia sp. (Dictyoceratida). Sponges were haphazardly sampled (monthly) over a period of 1 year. Histological analysis of samples established the sexuality, development, seasonality, gametogenesis and fecundity of the two species, as well as the effects of temperature on reproduction. I. basta is oviparous, whereas Ircinia sp. is viviparous. The mode of sexuality in I. basta could not be determined, because male propagules were not detected, whereas Ircinia sp. is a simultaneous hermaphrodite. Reproduction in I. basta is unique within the verongids and co-occurring oviparous species, with peak reproduction occurring at the minimum annual temperature (23°C) and spawning occurring as the temperature increased above 23.4°C. Reproduction in Ircinia sp. corresponded to patterns reported for other viviparous GBR species, with an increase in reproductive propagules, peak sperm release, fertilisation and spawning occurring at temperatures above 25°C. Fecundity in I. basta and Ircinia sp. is high compared with other sponge species in the region, which may contribute to their apparent abundance on the GBR