The McMurdo Dry Valleys of Antarctica are an extreme polar desert. Mineral soils support subsurface microbial communities and translucent rocks support development of hypolithic communities on ventral surfaces in soil contact. Despite significant research attention, relatively little is known about taxonomic and functional diversity or their inter-relationships. Here we report a combined diversity and functional interrogation for soil and hypoliths of the Miers Valley in the McMurdo Dry Valleys of Antarctica. The study employed 16S rRNA fingerprinting and high throughput sequencing combined with the GeoChip functional microarray. The soil community was revealed as a highly diverse reservoir of bacterial diversity dominated by actinobacteria. Hypolithic communities were less diverse and dominated by cyanobacteria. Major differences in putative functionality were that soil communities displayed greater diversity in stress tolerance and recalcitrant substrate utilization pathways, whilst hypolithic communities supported greater diversity of nutrient limitation adaptation pathways. A relatively high level of functional redundancy in both soil and hypoliths may indicate adaptation of these communities to fluctuating environmental conditions.

This study investigated the impacts of nutrient enrichment on intertidal biofilm microbial communities and on larval metamorphosis of invertebrates. We modulated the nutrient levels in the water column during biofilm development and examined the resulting biofilms for bacterial and diatom community composition using 2 DNA fingerprinting techniques and microscopic examination, respectively. Results of both terminal-restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis (DGGE) analyses indicated that the nutrient enrichment treatment altered the biofilm bacterial communities relative to the control. Biofilms that had different microbial compositions were tested for their effects on larval metamorphosis of the polychaete Hydroides elegans, the barnacle Balanus amphitrite, and the slipper limpet Crepidula onyx. We showed that nutrient enrichment in the water column effectively changed the biofilm composition in ways that increased its inductiveness for larval metamorphosis of C. onyx and B. amphitrite, but not of H. elegans. This study highlights the apparent importance of nutrient enrichment in influencing the intertidal biofilm composition directly and the invertebrates indirectly. KEY WORDS: Bacteria · Biofilms · Larvae · Nutrients Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 358: [41][42][43][44][45][46][47][48][49][50] 2008 Although some attention has been paid to the direct inductive effects of nutrient enrichment on larval metamorphosis (e.g. Fitt & Coon 1992), there may be indirect effects of nutrient enrichment through biofilms. Whether nutrient enrichment is effective in changing the biofilm composition in ways that alter its effects on larval metamorphosis remains unknown. Furthermore, it was demonstrated that nutrient enrichment could cause changes in the composition of intertidal communities even though the mechanisms underlying those changes were not understood (e.g. Morris & Keough 2003). Therefore, our objective was to investigate the role of nutrients on biofilms, and consequently on the metamorphosis of invertebrate larvae, which affects the recruitment process and hence the composition of intertidal communities.In this study, we developed biofilms in the field under nutrient enrichment and control conditions; the nutrient levels in the water column were modulated by using a fertilizer which releases a cocktail of nutrients that are representative of those being transferred to coastal areas (Morris & Keough 2003). Because of the importance of bacteria and diatoms on larval metamorphosis (e.g. Qian et al. 2003, Lau et al. 2005, Chiu et al. 2007), resulting biofilms were examined for diatom and bacterial cell densities and community composition. Then we tested the effects of the biofilms on larval metamorphosis of the polychaete Hydroides elegans, the barnacle Balanus amphitrite, and the slipper limpet Crepidula onyx. Biofilms are one of the key natural inductive cues for the larval metamorphosis of...

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