Spatial Scales of Bacterial Diversity in Cold-Water Coral Reef Ecosystems

Background: Cold-water coral reef ecosystems are recognized as biodiversity hotspots in the deep sea, but insights into their associated bacterial communities are still limited. Deciphering principle patterns of bacterial community variation over multiple spatial scales may however prove critical for a better understanding of factors contributing to cold-water coral reef stability and functioning. Methodology/Principal Findings: Bacterial community structure, as determined by Automated Ribosomal Intergenic Spacer Analysis (ARISA), was investigated with respect to (i) microbial habitat type and (ii) coral species and color, as well as the three spatial components (iii) geomorphologic reef zoning, (iv) reef boundary, and (v) reef location. Communities revealed fundamental differences between coral-generated (branch surface, mucus) and ambient microbial habitats (seawater, sediments). This habitat specificity appeared pivotal for determining bacterial community shifts over all other study levels investigated. Coral-derived surfaces showed species-specific patterns, differing significantly between Lophelia pertusa and Madrepora oculata, but not between L. pertusa color types. Within the reef center, no community distinction corresponded to geomorphologic reef zoning for both coral-generated and ambient microbial habitats. Beyond the reef center, however, bacterial communities varied considerably from local to regional scales, with marked shifts toward the reef periphery as well as between different in- and offshore reef sites, suggesting significant biogeographic imprinting but wea

Evidence of nitrification and denitrification in high and low microbial abundance sponges

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

Inter- and intra-habitat bacterial diversity associated with cold-water corals

The discovery of large ecosystems of cold-water corals (CWC), stretching along continental margins in depths of hundreds to thousands of meters, has raised many questions regarding their ecology, biodiversity and relevance as deep-sea hard-ground habitat. This study represents the first investigation that explicitly targets bacterial diversity from distinct microbial habitats associated with the cosmopolitan reef-building coral Lophelia pertusa, and also compares natural (fjord) and controlled (aquarium) conditions. Coral skeleton surface, coral mucus, ambient seawater and reef sediments clearly showed habitat-specific differences in community structure and operational taxonomic unit (OTU) number. Especially in the natural environment, bacterial communities associated with coral-generated habitats were significantly more diverse than those present in the surrounding, non-coral habitats, or those in artificial coral living conditions (fjord vs aquarium). These findings strongly indicate characteristic coral-microbe associations and, furthermore, suggest that the variety of coral-generated habitats within reef systems promotes microbial diversity in the deep ocean