"Never Waste A Good Crisis"

  • The latest on nitrogen-fixing bacteria in corals
    Tuesday, March 31, 2009 - 16:09

    ckellogg

    Montipora capitata, aka "rice coral," image found here.

     

    Coral microbial ecology starts with two basic questions: "Who is there?" and "What are they doing?"  This recent paper by Olson et al. 2009 touches on both by examining the diversity of nitrogen-fixing bacteria in Hawaiian corals.  Here's the abstract:


    The primary productivity of coral–dinoflagellate symbiosis is classically viewed as nitrogen (N)-limited. However, the recent discovery of N-fixing bacteria residing within coral tissues challenges this view. This study investigated the diversity and abundance of N-fixing bacteria associated with Hawaiian corals of the genus Montipora. Phylogenetic analysis of a partial sequence of the nitrogenase gene (nifH), revealed a diverse group of N-fixing bacteria in association with Montipora capitata and Montipora flabellata. These nifHsequences were closely affiliated with known taxa in α-, β-, γ-, and δ-proteobacteria, as well as cyanobacteria. Gamma-proteobacteria were the dominant bacterial class represented, and bacteria closely related to the genus Vibrio were the prevailing group within this class. Quantitative PCR was used to evaluate the abundance of the dominant class of N-fixing bacteria from different parts of four M. capitata colonies. The abundance of the dominant γ-proteobacteria was positively correlated (p = 0.001) with the abundance of symbiotic dinoflagellates, suggesting a physiological relationship between the two coral symbionts. The evidence obtained in this study suggests that N-limitation may not be a major regulator of the productivity of dinoflagellate symbionts of corals, but provides impetus for renewed investigation into N-cycling in this multi-partner symbiosis.

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    To find the article, go here.

    Olson, N.D., T.D. Ainsworth, R.D. Gates, and M. Takabayashi. 2009. Diazotrophic bacteria associated with Hawaiian Montipora corals: Diversity and abundance in correlation with symbiotic dinoflagellates.  Journal of Experimental Marine Biology and Ecology 371(2):140-146.

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  • Archaea associated with coral mucus
    Monday, March 30, 2009 - 21:38

    morrisp

    ~Granulated Mushroom Coral, Fungia granulosa, image found here~

    My group in the Hollings Marine Laboratory is interested in the functional potential of coral-associated microbial communities, so of course we found the article by Siboni et al. 2008 published in Environmental Microbiology to be a fascinating piece of what will probably prove to be a very complex puzzle.  Here's the abstract:   

    Diversity, distribution and genetic comparison of Archaea associated with the surface mucus of corals from three genera, namely Acanthastrea sp., Favia sp. and Fungia sp., from the Gulf of Eilat, Israel and from Heron Island, Australia were studied. Sequencing of the 16S rRNA gene of the coral-associated Archaea revealed dominance of Crenarchaeota (79%, on average). In this phylum, 87% of the sequences were similar (≥ 97%) to the Thermoprotei, with 76% of these being similar (≥ 97%) to the ammonium oxidizer, Nitrosopumilus maritimus. Most of the coral-associated euryarchaeotal sequences (69%) were related to marine group II, while other euryarchaeotal clades were found to be related to anaerobic methanotrophs (8%), anaerobic nitrate reducers (i.e. denitrification, 15%) and marine group III (8%). Most of the crenarchaeotal and euryarchaeotal coral-associated 16S rRNA gene sequences from Heron Island (61%) and from the Gulf of Eilat (71%) were closely related (≥ 97%) to sequences previously derived from corals from the Virgin Islands. Analysis of archaeal amoA sequences obtained from the fungiid coral, Fungia granulosa, divided into three clades, all related to archaeal sequences previously obtained from the marine environment. These sequences were distantly related to amoA sequences previously found in association with other coral species. Preliminary experiments suggest that there is active oxidation of ammonia to nitrite in the mucus of F. granulosa. Thus, coral-associated Archaea may contribute to nitrogen recycling in the holobiont, presumably by acting as a nutritional sink for excess ammonium trapped in the mucus layer, through nitrification and denitrification processes.

    ~~~~~

    To find the article, go here:

    Siboni, N., E. Ben-Dov, A. Sivan and A. Kushmaro.  2008.  Global distribution and diversity of coral-associated Archaea and their possible role in the coral holobiont nitrogen cycle.  Environmental Microbiology 10(11):2979-2990.

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  • Caribbean Coral Reefs and Reef Fish Assemblages...
    Sunday, March 29, 2009 - 18:21

    morrisp

    If you're looking for that perfect reference to show the critical link between coral health and fish populations, then this reference might be for you.  Here's the summary: 

    Profound ecological changes are occurring on coral reefs throughout the tropics, with marked coral cover losses and concomitant algal increases, particularly in the Caribbean region. Historical declines in the abundance of large Caribbean reef fishes likely reflect centuries of overexploitation. However, effects of drastic recent degradation of reef habitats on reef fish assemblages have yet to be established. By using meta-analysis, we analyzed time series of reef fish density obtained from 48 studies that include 318 reefs across the Caribbean and span the time period 1955 to 2007. Our analyses show that overall reef fish density has been declining significantly for more than a decade, at rates that are consistent across all subregions of the Caribbean basin (2.7% to 6.0% loss per year) and in three of six trophic groups. Changes in fish density over the past half-century are modest relative to concurrent changes in benthic cover on Caribbean reefs. However, the recent significant decline in overall fish abundance and its consistency across several trophic groups and among both fished and nonfished species indicate that Caribbean fishes have begun to respond negatively to habitat degradation.

    Published online 19 March 2009:

    Paddack et al. 2009.  Recent Region-wide Declines in Caribbean Reef Fish Abundance.  Current Biology.  doi:10.1016/j.cub.2009.02.041. 

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  • Earth Hour
    Saturday, March 28, 2009 - 13:02

    morrisp

    Vote Earth Tree by Earth Hour Global.

    ~Earth Hour, 28 March 2009, 8:30-9:30 pm, lights out!~

    (Image found here).

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  • NPR's Science Friday (27 March 2009)
    Friday, March 27, 2009 - 19:57

    morrisp

    In case you missed it, head over to NPR and listen to today's Science Friday podcast 'Ocean Priorities'...where you'll find an interesting interview with NOAA's new Administrator, Jane Lubchenco.  

    And while you're there, why not take a listen to their podcast from 11 July 2008 titled 'A Coral Catastrophe?'   

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