Marine sponges constitute major parts of coral reefs and deep-water communities. They often harbour high amounts of phylogenetically and physiologically diverse microbes, which are so far poorly characterized. Many of these sponges regulate their internal oxygen concentration by modulating their ventilation behaviour providing a suitable habitat for both aerobic and anaerobic microbes. In the present study, both aerobic (nitrification) and anaerobic (denitrification, anammox) microbial processes of the nitrogen cycle were quantified in the sponge Geodia barretti and possible involved microbes were identified by molecular techniques. Nitrification rates of 566 nmol N cm(-3) sponge day(-1) were obtained when monitoring the production of nitrite and nitrate. In support of this finding, ammonia-oxidizing Archaea (crenarchaeotes) were found by amplification of the amoA gene, and nitrite-oxidizing bacteria of the genus Nitrospira were detected based on rRNA gene analyses. Incubation experiments with stable isotopes ((15)NO(3)(-) and (15)NH(4)(+)) revealed denitrification and anaerobic ammonium oxidation (anammox) rates of 92 nmol N cm(-3) sponge day(-1) and 3 nmol N cm(-3) sponge day(-1) respectively. Accordingly, sequences closely related to 'Candidatus Scalindua sorokinii' and 'Candidatus Scalindua brodae' were detected in 16S rRNA gene libraries. The amplification of the nirS gene revealed the presence of denitrifiers, likely belonging to the Betaproteobacteria. This is the first proof of anammox and denitrification in the same animal host, and the first proof of anammox and denitrification in sponges. The close and complex interactions of aerobic, anaerobic, autotrophic and heterotrophic microbial processes are fuelled by metabolic waste products of the sponge host, and enable efficient utilization and recirculation of nutrients within the sponge-microbe system. Since denitrification and anammox remove inorganic nitrogen from the environment, sponges may function as so far unrecognized nitrogen sinks in the ocean. In certain marine environments with high sponge cover, sponge-mediated nitrogen mineralization processes might even be more important than sediment processes.

Aerobic and anaerobic microbial key processes were quantified and compared to microbial numbers and morphological structure in Mediterranean sponges. Direct counts on histological sections stained with DAPI showed that sponges with high microbial abundances (HMA sponges) have a denser morphological structure with a reduced aquiferous system compared to low microbial abundance (LMA) sponges. In Dysidea avara, the LMA sponge, rates of nitrification and denitrification were higher than in the HMA sponge Chondrosia reniformis, while anaerobic ammonium oxidation and sulfate reduction were below detection in both species. This study shows that LMA sponges may host physiologically similar microbes with comparable or even higher metabolic rates than HMA sponges, and that anaerobic processes such as denitrification can be found both in HMA and LMA sponges. A higher concentration of microorganisms in the mesohyl of HMA compared to LMA sponges may indicate a stronger retention of and, hence, a possible benefit from associated microbes.

Wave energy devices are novel structures in the marine environment and, as such, provide a unique habitat for biofouling organisms. In this study, destructive scrape samples and photoquadrats were used to characterise the temperate epibenthic community present on prototypes of the Pelamis wave energy converter. The biofouling observed was extensive and diverse with 115 taxa recorded including four non-native species. Vertical zonation was identified on the sides of the device, with an algae-dominated shallow subtidal area and a deeper area characterised by a high proportion of suspension-feeding invertebrates. Differences in species composition and biomass were also observed between devices, along the length of the device and between sampling dates. This research provides an insight into the variation of biofouling assemblages on a wave energy device as well as the potential technical and ecological implications associated with biofouling on marine renewable energy structures.

The oxygen dynamics and pumping behavior in Dysidea avara and Chondrosia reniformis (Porifera, Demospongiae) were investigated using oxygen microelectrodes and heated thermistor flow sensors. Both field and laboratory experiments showed the common occurrence of low oxygenation approaching anoxia in both species, lasting up to 1 h. Strong temporal and spatial heterogeneity of oxygen concentrations were observed with replicate oxygen profile series across the sponge surface, though tissue close to an osculum was generally better oxygenated than deeper in the sponge body. Because of observed lag times between a pumping event and the respective oxygenation response, the state of oxygenation of sponge tissue could only be partially attributed to its pumping activity. Ambient flow also influenced oxygenation patterns of sponges. Larger individuals possessing a functional aquiferous system regulated their pumping activity according to the ambient flow regime, whereas a small D. avara sponge, yet to possess its first osculum, was passively oxygenated by ambient flow and became anoxic approximately 30 min after ambient flow was stopped in its laboratory tank. These studies showed (1) sponge tissue metabolism switched frequently from aerobic to anaerobic, (2) temporally and spatially dynamic oxygen-depleted regions were commonly found within those sponges, both in captivity and in the field, and (3) tissue oxygenation was regulated both by active behavior (pumping) and passive environmental events (ambient water flow). We concluded that the metabolism of both sponge cells and sponge microbes will be influenced by the sponges' ability to control oxygen concentrations in different regions of its body at any particular time. In addition, when a sponge is actively pumping in a particular region of its body, higher oxygen concentrations will favor aerobic symbionts and aerobic metabolism, whereas when active pumping ceases, anaerobic symbionts and anaerobic tissue metabolism will be favored.