Variability in Host Specificity and Functional Potential of Antarctic Sponge-Associated Bacterial Communities

Sponge-associated microorganisms are essential for sponge survival. They play an important role in recycling nutrients and, therefore, in the maintenance of the ecosystem. These microorganisms are diverse, species-specific, and different from those in the surrounding seawater. Bacterial sponge symbionts have been extensively studied in the tropics; however, little is known about these microorganisms in sponges from high-latitude environments. Sponges can cover up to 80% of the benthos in Antarctica and are crucial architects for the marine food web. In this study, we present analyses of the bacterial symbionts of three sponges: Haliclona (Rhizoniera) sp., Hymeniacidon torquata, and Isodictya kerguelenensis from the Western Antarctic Peninsula (WAP) with the aim to determine variations on the specificity of the bacteria–sponge interactions and potential signatures on their predicted functional profiles. We use high-throughput 16S rRNA gene sequencing of 30 sponge individuals inhabiting South Bay (Palmer Archipelago, WAP) to describe their microbiome taxonomy and diversity and predict potential functional profiles based on this marker gene. Our work shows similar bacterial community composition profiles among the same sponge species, although the symbiotic relationship is not equally conserved among the three Antarctic sponges. The number of species-specific core operational taxonomic units (OTUs) of these Antarctic sponges was low, with important differences between the total abundance accounted for these OTUs. Only eight OTUs were shared between the three sponge species. Analyses of the functional potential revealed that despite the high host–symbiont specificity, the inferred functions are conserved among these microbiomes, although with differences in the abundance of specific functions. H. torquata showed the highest level of intra-specificity and a higher potential of pathways related to energy metabolism, metabolisms of terpenoids and polyketides, and biosynthesis of other secondary metabolites. Overall, this work shows variations in the specificity of the sponge-associated bacterial communities, differences in how hosts and symbionts establish their relations, and in their potential functional capabilities.

Impact of growth media and pressure on the diversity and antimicrobial activity of isolates from two species of hexactinellid sponge

Access to deep-sea sponges brings with it the potential to discover novel antimicrobial candidates, as well as novel cold- and pressure-adapted bacteria with further potential clinical or industrial applications. In this study, we implemented a combination of different growth media, increased pressure and high-throughput techniques to optimize recovery of isolates from two deep-sea hexactinellid sponges, Pheronema carpenteri and Hertwigia sp., in the first culture-based microbial analysis of these two sponges. Using 16S rRNA gene sequencing for isolate identification, we found a similar number of cultivable taxa from each sponge species, as well as improved recovery of morphotypes from P. carpenteri at 22–25 °C compared to other temperatures, which allows a greater potential for screening for novel antimicrobial compounds. Bacteria recovered under conditions of increased pressure were from the phyla Proteobacteria , Actinobacteria and Firmicutes , except at 4 %O2/5 bar, when the phylum Firmicutes was not observed. Cultured isolates from both sponge species displayed antimicrobial activity against Micrococcus luteus, Staphylococcus aureus and Escherichia coli .

Sponge-Associated Amphipod Communities as Bioindicators for Pollution

<p>Pollution negatively impacts organisms across all marine ecosystems. Coastal areas are particularly vulnerable to pollution due to their proximity to human settlements. Amphipods are commonly used as bioindicators to monitor pollution burdens, due to their high sensitivities and their ubiquity. Pollution can reduce amphipod abundance, species richness, evenness and diversity. Community structure, proportionality of adults to juveniles and sex ratios may also be affected. Sponges often harbour high densities of amphipods, offering food, refuge and nurseries to their symbionts. Sponge-associated amphipods differ in their level of specialization on their host. This study provides first insights into the usefulness of sponge-associated amphipod communities as bioindicators. For this, it hypothesized that amphipod densities, species diversity, community structure, sex ratio and age proportionality will differ according to pollution levels. To test this, sponges were collected from three sites with varying degrees of pollution in Wellington Harbour. The sponges were weighed, and their volume was measured. They were dissected and their amphipods were identified to species level, counted, measured (length) and their sex and life cycle stage (adult or juvenile) were recorded. From this data, amphipod densities, species richness, evenness and Shannon-Wiener diversity indices were calculated and compared among pollution levels. Community structure was also compared between sites and sponge species. Pollution level significantly affected species richness, evenness, diversity and community structure. The highest values for species richness, evenness and diversity were found in sponges from the least polluted. The lowest levels of these factors were found in sponges from the most polluted site. Sponges from the intermediate site generally harboured moderate richness, evenness and diversity compared to the other sites. Community composition was significantly affected by pollution, although effect sizes differed between sponge species. Higher pollution levels seemed to favour dominance of species that are better adapted to living in sponges. Generalists seemed to thrive in low to intermediate pollution levels. The majority of sex ratios measured had a female bias, which appeared to increase with increasing pollution although the difference was not statistically significant. The proportion of adults also showed a non-significant increase with pollution level. There was no significant difference in amphipod abundance per litre of sponge tissue between pollution levels, possibly because pollution levels may have been too low to cause a reduction in amphipod density. These results show that sponge-associated amphipod communities are useful as bioindicators, as amphipod diversity, richness and evenness were significantly reduced by pollution and the sponge association allows for these community-scale comparisons to be made within an easily measurable framework. Species evenness in particular provided an accurate indication of different pollution levels.</p>

Sponge-Associated Amphipod Communities as Bioindicators for Pollution

<p>Pollution negatively impacts organisms across all marine ecosystems. Coastal areas are particularly vulnerable to pollution due to their proximity to human settlements. Amphipods are commonly used as bioindicators to monitor pollution burdens, due to their high sensitivities and their ubiquity. Pollution can reduce amphipod abundance, species richness, evenness and diversity. Community structure, proportionality of adults to juveniles and sex ratios may also be affected. Sponges often harbour high densities of amphipods, offering food, refuge and nurseries to their symbionts. Sponge-associated amphipods differ in their level of specialization on their host. This study provides first insights into the usefulness of sponge-associated amphipod communities as bioindicators. For this, it hypothesized that amphipod densities, species diversity, community structure, sex ratio and age proportionality will differ according to pollution levels. To test this, sponges were collected from three sites with varying degrees of pollution in Wellington Harbour. The sponges were weighed, and their volume was measured. They were dissected and their amphipods were identified to species level, counted, measured (length) and their sex and life cycle stage (adult or juvenile) were recorded. From this data, amphipod densities, species richness, evenness and Shannon-Wiener diversity indices were calculated and compared among pollution levels. Community structure was also compared between sites and sponge species. Pollution level significantly affected species richness, evenness, diversity and community structure. The highest values for species richness, evenness and diversity were found in sponges from the least polluted. The lowest levels of these factors were found in sponges from the most polluted site. Sponges from the intermediate site generally harboured moderate richness, evenness and diversity compared to the other sites. Community composition was significantly affected by pollution, although effect sizes differed between sponge species. Higher pollution levels seemed to favour dominance of species that are better adapted to living in sponges. Generalists seemed to thrive in low to intermediate pollution levels. The majority of sex ratios measured had a female bias, which appeared to increase with increasing pollution although the difference was not statistically significant. The proportion of adults also showed a non-significant increase with pollution level. There was no significant difference in amphipod abundance per litre of sponge tissue between pollution levels, possibly because pollution levels may have been too low to cause a reduction in amphipod density. These results show that sponge-associated amphipod communities are useful as bioindicators, as amphipod diversity, richness and evenness were significantly reduced by pollution and the sponge association allows for these community-scale comparisons to be made within an easily measurable framework. Species evenness in particular provided an accurate indication of different pollution levels.</p>

The influence of sponge-dwelling gobies (Elacatinus horsti) on the feeding efficiency of their Caribbean tube sponge ( Aplysina sp.) hosts

Mutualistic associations between benthic marine invertebrates and reef taxa are common. Sponge-dwelling gobies benefit from protection within sponge tubes and greater food availability. Sponge-dwelling gobies are hypothesized to increase sponge pump rates by consuming polychaete parasites, but such increases have not yet been demonstrated. We investigated the association between sponge-dwelling gobies (Elacatinus horsti) and two species of tube sponge (Aplysina lacunosa and Aplysina archeri) in Bonaire, Caribbean Netherlands. We visually assessed goby presence in sponges and used in situ methods with fluorescein dye to measure estimate feeding rates via pump rates. Aplysina archeri were more likely to host a goby than A. lacunosa. For both sponge species, pump rates of tubes with gobies were higher on average than those of tubes without gobies. Our observations, therefore, suggest that E. horsti associations with Aplysina are likely mutualistic relationships in which sponges benefit from higher feeding rates when gobies are present.

Sponge bioerosion and habitat degradation on Indonesian coral reefs

<p>Coral reefs are among the most diverse ecosystems on the planet, yet they are also sensitive to anthropogenic disturbances that can degrade these systems. On many degraded reefs, large increases in bioeroding sponge abundance have occurred. On healthy reefs these sponges contribute to species diversity and habitat complexity, however there is growing concern that their proliferation on degraded reefs could lead to a state of net-erosion. In the Southeast Asian Indo-Pacific, the ecology of bioeroding sponges in relation to coral degradation has been poorly studied compared to other coral reef regions. This thesis aims to increase our understanding of the ecology of these sponges in the Wakatobi region of Indonesia, and their likely trajectory if reefs continue to degrade in the region. My first research chapter aimed to identify the common bioeroding sponge species of the Wakatobi. This was achieved through in-water surveys, and subsequent spicule and phylogenetic analysis. This resulted in the identification of eight commonly occurring Wakatobi bioeroding sponge species, two of which are described for the first time. The assemblage composition was distinctly different from the only other bioeroding sponge study in Indonesian waters (Calcinai et al. 2005), highlighting the need for more clionaid taxonomic information from the region. Having identified the common bioeroding sponge species in the region, my second chapter assessed the major environmental drivers of the abundance and assemblage composition of these sponges. Abundance surveys were conducted at 11 reef sites characterised by different environmental conditions and states of reef health. Bioeroding sponges occupied 8.9% of suitable substrate, and differences in abundance and assemblage composition were primarily attributed to differences in the availability of dead substrate. However, abundance was lowest at a sedimented and turbid reef, despite abundant dead substrate availability. This indicates a limited resilience in some species to conditions associated with terrestrial run-off and that not all forms of reef degradation are beneficial for bioeroding sponges. The capacity to increase spatial occupation of degraded reefs is also dependent upon larval recruitment and my third chapter was a two year recruitment study using in situ experimental calcareous blocks. Recruitment occurred rapidly and consistently with bioeroding sponges recruiting to approximately 70% of experimental blocks and exhibiting a preference for settlement on uncolonised dead calcareous substrates. The importance of substrate settlement cues and extent of larval dispersal appeared to differ between species, indicative of different recruitment mechanisms. Any significant increase in the availability of exposed calcareous substrate (e.g. following a mass coral bleaching event) is therefore likely to result in widespread increases in bioeroding sponge recruitment. Surveys conducted in my second research chapter revealed that two of the three locally abundant zooxanthellate bioeroding species were absent from a highly turbid reef, Sampela. My fourth research chapter investigated whether this was due to light limitation by examining the photoacclimatory capabilities of the Symbiodinium photosymbionts of Cliona aff. viridis n. sp. A. PAM chlorophyll fluorometry was employed in a 25 day shading experiment and Symbiodinium of C. aff. viridis n. sp. A demonstrated an ability to photoacclimate to extreme light reduction and recover quickly when conditions returned to normal. My results demonstrate that the absence of this species at Sampela is not due to light limitation but possibly due to other stressors associated with turbidity, e.g. suspended sediment. My final chapter was an assessment of the environmental drivers of rates of bioerosion in Spheciospongia cf. vagabunda, a common species in the Wakatobi. Erosion rates were determined from changes in dry-weight of calcareous substrates with attached grafts of S. cf. vagabunda after a year deployment across seven reef sites. The average bioerosion rate was 12.0 kg m⁻² sponge tissue yr⁻¹ (± 0.87 SE), but differed between sites and was negatively correlated with settled sediment depth. Bioerosion by this species can play a significant part in the carbonate budget on reefs where it is abundant (up to 20% of available substrate on some reefs in the Wakatobi) but is likely reduced on highly sedimented reefs. In summary, the Wakatobi bioeroding sponge assemblage is diverse and overall, both adult abundance and recruitment are primarily driven by the availability of dead calcareous substrates. Therefore, further coral mortality and a subsequent rise in the availability of dead substrate in the region is likely to result in increased abundance of bioeroding sponges. However, not all forms of reef degradation will benefit these sponges; turbid and sedimented reefs will likely constitute stressful habitats for some bioeroding sponge species and assemblages in these environments will be comprised of fewer more resilient species.</p>

Sponge bioerosion and habitat degradation on Indonesian coral reefs

<p>Coral reefs are among the most diverse ecosystems on the planet, yet they are also sensitive to anthropogenic disturbances that can degrade these systems. On many degraded reefs, large increases in bioeroding sponge abundance have occurred. On healthy reefs these sponges contribute to species diversity and habitat complexity, however there is growing concern that their proliferation on degraded reefs could lead to a state of net-erosion. In the Southeast Asian Indo-Pacific, the ecology of bioeroding sponges in relation to coral degradation has been poorly studied compared to other coral reef regions. This thesis aims to increase our understanding of the ecology of these sponges in the Wakatobi region of Indonesia, and their likely trajectory if reefs continue to degrade in the region. My first research chapter aimed to identify the common bioeroding sponge species of the Wakatobi. This was achieved through in-water surveys, and subsequent spicule and phylogenetic analysis. This resulted in the identification of eight commonly occurring Wakatobi bioeroding sponge species, two of which are described for the first time. The assemblage composition was distinctly different from the only other bioeroding sponge study in Indonesian waters (Calcinai et al. 2005), highlighting the need for more clionaid taxonomic information from the region. Having identified the common bioeroding sponge species in the region, my second chapter assessed the major environmental drivers of the abundance and assemblage composition of these sponges. Abundance surveys were conducted at 11 reef sites characterised by different environmental conditions and states of reef health. Bioeroding sponges occupied 8.9% of suitable substrate, and differences in abundance and assemblage composition were primarily attributed to differences in the availability of dead substrate. However, abundance was lowest at a sedimented and turbid reef, despite abundant dead substrate availability. This indicates a limited resilience in some species to conditions associated with terrestrial run-off and that not all forms of reef degradation are beneficial for bioeroding sponges. The capacity to increase spatial occupation of degraded reefs is also dependent upon larval recruitment and my third chapter was a two year recruitment study using in situ experimental calcareous blocks. Recruitment occurred rapidly and consistently with bioeroding sponges recruiting to approximately 70% of experimental blocks and exhibiting a preference for settlement on uncolonised dead calcareous substrates. The importance of substrate settlement cues and extent of larval dispersal appeared to differ between species, indicative of different recruitment mechanisms. Any significant increase in the availability of exposed calcareous substrate (e.g. following a mass coral bleaching event) is therefore likely to result in widespread increases in bioeroding sponge recruitment. Surveys conducted in my second research chapter revealed that two of the three locally abundant zooxanthellate bioeroding species were absent from a highly turbid reef, Sampela. My fourth research chapter investigated whether this was due to light limitation by examining the photoacclimatory capabilities of the Symbiodinium photosymbionts of Cliona aff. viridis n. sp. A. PAM chlorophyll fluorometry was employed in a 25 day shading experiment and Symbiodinium of C. aff. viridis n. sp. A demonstrated an ability to photoacclimate to extreme light reduction and recover quickly when conditions returned to normal. My results demonstrate that the absence of this species at Sampela is not due to light limitation but possibly due to other stressors associated with turbidity, e.g. suspended sediment. My final chapter was an assessment of the environmental drivers of rates of bioerosion in Spheciospongia cf. vagabunda, a common species in the Wakatobi. Erosion rates were determined from changes in dry-weight of calcareous substrates with attached grafts of S. cf. vagabunda after a year deployment across seven reef sites. The average bioerosion rate was 12.0 kg m⁻² sponge tissue yr⁻¹ (± 0.87 SE), but differed between sites and was negatively correlated with settled sediment depth. Bioerosion by this species can play a significant part in the carbonate budget on reefs where it is abundant (up to 20% of available substrate on some reefs in the Wakatobi) but is likely reduced on highly sedimented reefs. In summary, the Wakatobi bioeroding sponge assemblage is diverse and overall, both adult abundance and recruitment are primarily driven by the availability of dead calcareous substrates. Therefore, further coral mortality and a subsequent rise in the availability of dead substrate in the region is likely to result in increased abundance of bioeroding sponges. However, not all forms of reef degradation will benefit these sponges; turbid and sedimented reefs will likely constitute stressful habitats for some bioeroding sponge species and assemblages in these environments will be comprised of fewer more resilient species.</p>

Measuring the Effects of Microplastics on Sponges

<p>Microplastics (MP’s) are ubiquitous throughout the marine environment, and are derived from either direct production or from the fragmentation (to <5mm) of larger plastic pollution. Recently concern has intensified as the extent of MP pollution and its presence in the marine environment has been highlighted. Literature concerning concentrations of microplastics indicates an increasing occurrence in the marine environment, from coastal beaches to deep sea sediments. In addition, the effects microplastics have on marine organisms are well documented, with studies ranging from large pelagic animals to benthic filter feeders. However to date, there are few data on how MPs influence Porifera. Sponges are an important component of temperate benthic ecosystems, providing a range of important functional roles. Sponges are able to adapt to many environments by exploiting a variety of food sources, from dissolved organic matter to small crustaceans. Regardless of this, sponges feed primarily on picoplankton, and are able to retain up to 99% of these from seawater. The impact microplastics have on these suspension feeders is becoming of increasing concern, and previous research has centred primarily on sponge feeding or responses to sediments. As such, this thesis is the first to focus on the metabolic responses of sponges to MPs. To examine this, two response variables were measured: O₂ consumption (Respiration) and feeding (Retention efficiency). To examine the effects of MP on sponge respiration, two temperate sponge species (Tethya bergquistae and Crella incrustans) were exposed to two different sized plastic particles (1 μm and 6 μm) at two different concentrations (200,000 and 400,000 beads per mL). Results indicate that sponges are resilient to MP pollution. The only significant result was the effect of MP size on the respiration rates on Tethya bergquistae (P = 0.001), but there were no other significant main effects or interactions. Marine particulates come in many shapes and sizes, as such the retention abilities of temperate sponges were tested after exposure to different types and sizes of particulates. This was achieved by subjecting the same two sponge species (Crella incrustans and Tethya bergquistae) to two microplastic (1 μm & 6 μm), two sediment (1 μm & 6 μm) and two “Food” (raw sea water and Isochrysis galbana) treatments. This experiment showed some significant retention differences, but these differences were difficult to explain and largely inconclusive. This has highlighted the need for further investigation into the effects of: mixed treatments (i.e. sediments + plastics together) and varying plastic shapes (sphere + fibre + fragment). Finally, there is a crucial gap in knowledge regarding the fate of microplastics after ingestion by sponges. This research outlines the potential for temperate sponges to be resilient to microplastics particles when considering respiration rates. In addition, this study also outlines the variable nature of Crella incrustans and Tethya bergquistae concerning particulate retention. As the MP concentrations used in this thesis are very high and are unlikely to be found in New Zealand in the near future, this thesis therefore demonstrates the capability for sponges to be resilient to microplastic pollution. The outcomes of my thesis highlight the importance of understanding the impacts of microplastics on benthic organisms. The marine environment is dynamic and organisms are susceptible to a multitude of stressors. As such, there is a need to explore interactions between multiple factors at the same time.</p>

Measuring the Effects of Microplastics on Sponges

<p>Microplastics (MP’s) are ubiquitous throughout the marine environment, and are derived from either direct production or from the fragmentation (to <5mm) of larger plastic pollution. Recently concern has intensified as the extent of MP pollution and its presence in the marine environment has been highlighted. Literature concerning concentrations of microplastics indicates an increasing occurrence in the marine environment, from coastal beaches to deep sea sediments. In addition, the effects microplastics have on marine organisms are well documented, with studies ranging from large pelagic animals to benthic filter feeders. However to date, there are few data on how MPs influence Porifera. Sponges are an important component of temperate benthic ecosystems, providing a range of important functional roles. Sponges are able to adapt to many environments by exploiting a variety of food sources, from dissolved organic matter to small crustaceans. Regardless of this, sponges feed primarily on picoplankton, and are able to retain up to 99% of these from seawater. The impact microplastics have on these suspension feeders is becoming of increasing concern, and previous research has centred primarily on sponge feeding or responses to sediments. As such, this thesis is the first to focus on the metabolic responses of sponges to MPs. To examine this, two response variables were measured: O₂ consumption (Respiration) and feeding (Retention efficiency). To examine the effects of MP on sponge respiration, two temperate sponge species (Tethya bergquistae and Crella incrustans) were exposed to two different sized plastic particles (1 μm and 6 μm) at two different concentrations (200,000 and 400,000 beads per mL). Results indicate that sponges are resilient to MP pollution. The only significant result was the effect of MP size on the respiration rates on Tethya bergquistae (P = 0.001), but there were no other significant main effects or interactions. Marine particulates come in many shapes and sizes, as such the retention abilities of temperate sponges were tested after exposure to different types and sizes of particulates. This was achieved by subjecting the same two sponge species (Crella incrustans and Tethya bergquistae) to two microplastic (1 μm & 6 μm), two sediment (1 μm & 6 μm) and two “Food” (raw sea water and Isochrysis galbana) treatments. This experiment showed some significant retention differences, but these differences were difficult to explain and largely inconclusive. This has highlighted the need for further investigation into the effects of: mixed treatments (i.e. sediments + plastics together) and varying plastic shapes (sphere + fibre + fragment). Finally, there is a crucial gap in knowledge regarding the fate of microplastics after ingestion by sponges. This research outlines the potential for temperate sponges to be resilient to microplastics particles when considering respiration rates. In addition, this study also outlines the variable nature of Crella incrustans and Tethya bergquistae concerning particulate retention. As the MP concentrations used in this thesis are very high and are unlikely to be found in New Zealand in the near future, this thesis therefore demonstrates the capability for sponges to be resilient to microplastic pollution. The outcomes of my thesis highlight the importance of understanding the impacts of microplastics on benthic organisms. The marine environment is dynamic and organisms are susceptible to a multitude of stressors. As such, there is a need to explore interactions between multiple factors at the same time.</p>

Interactions Between Sponges and Macroalgae on Temperate Rocky Reefs

<p>Changes in the distributions of organisms not only alter community composition and food web structure, but also can initiate important changes at the ecosystem level. Understanding the interactions between biotic and abiotic factors affecting species’ distribution patterns in temperate habitats is important for predicting responses to future environmental change. Sponges are important members of temperate rocky reefs assemblages that are influenced by a number of abiotic factors including water movement, light regime, inclination and stability of the substratum, as well as complex ecological interactions. The aim of this thesis was to investigate the interactions between sponges and macroalgae on shallow-water rocky reefs of Wellington, New Zealand, assessing if the distribution patterns of sponges are independent of algal populations. I used a combination of surveys, and manipulative field and laboratory experiments to explore the existence of interactions (positive or negative) between sponges and macroalgae and also to explore the effect of environmental factors on the distribution and abundance of temperate sponges. My first objective was to determine if the spatial distribution patterns of sponges are independent of macroalgae distribution and abundance at different sites on the Wellington south coast (Chapter 2). The results showed that abundance of most sponge species were strongly correlated with inclination, which supports previous studies in the northern hemisphere suggesting that sponge abundance and algal abundance are negatively correlated. In contrast, only a few sponge species were positively correlated with algal abundance. I then explored the positive interactions occurring between some sponges species and the presence of canopy-forming algae (Chapter 3). Results from this chapter suggest the canopy of Ecklonia radiata facilitates the existence of some sponge species such as Crella incrustans on vertical rocky walls. The removal of Ecklonia canopy led to a community dominated by turf algae, which corresponded with a decrease in sponge abundance and richness. My results suggest that the Ecklonia canopy facilitates the presence of some sponge species and allows their coexistence with turf algae underneath the canopy and also by altering immediate physical factors that may be detrimental for some sponge species. To further explore the existence of sponges and understory algae, I used an experimental approach (Chapter 4) to investigate the effect of the brown alga Zonaria turneriana on Leucetta sp. and also mechanisms involved in the interactions. However results from this chapter provided no evidence to support previous hypotheses that understory algae negatively affect sponges. In the last data chapter (Chapter 5), I studied sponges inhabiting different habitats in order to test if environmental variation affects the abundance and diversity of microorganisms, hence having the potential to affect the distribution and abundance of these species The stability observed in bacterial communities among specimens occupying different habitats suggests that environmental variation occurring in those habitats does not affect the stability of the community, and hence most likely does not radically alter the metabolism of these sponges. Although environmental factors such as light and sediment may have an effect on early sponge stages, other environmental (e.g. nutrients, temperature, wave action) and biotic factors, are more likely to influence the growth, survival and distribution of sponges on temperate rocky reefs. In summary, temperate sponge assemblages are strongly influenced by interactions between a number of abiotic and biotic factors. The outcomes of the ecological interactions are controlled by environment (e.g. influence of inclination on competition between sponges and understory algae) and at the same time, biological interactions (e.g. facilitation) can moderate the influence of abiotic factors such as light, sedimentation and wave action, thus facilitating the coexistence between sponge and macroalgae underneath the Ecklonia canopy. My thesis makes a significant contribution to our knowledge of temperate subtidal ecology, in terms of the effects of biotic and abiotic factors on sponge assemblages and also improves our knowledge of temperate patterns of sponge and macroalgal interactions. Finally, my thesis highlights the importance of small-scale environmental variation in influencing the structure and diversity of sponge assemblages and also increase our understanding of temperate rocky reefs sponges, especially on the less studied sponge assemblages occurring in Ecklonia stands on vertical rocky walls.</p>