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    Coral Mucus, The Unappreciated Slime of Saltwater

    A 2004 study published in the journal Nature has recently gained my attention, thanks to GBD contributor Tetsuo Otake. It isn’t anything radically new, but for a geek like myself I found the omission from my reading files appalling–because it’s quite a good read! The article, Coral mucus functions as an energy carrier and particle trap in […]

    Acropora at Low Tide

    A 2004 study published in the journal Nature has recently gained my attention, thanks to GBD contributor Tetsuo Otake. It isn’t anything radically new, but for a geek like myself I found the omission from my reading files appalling–because it’s quite a good read! The article, Coral mucus functions as an energy carrier and particle trap in the reef ecosystem, is an interesting look at the often ignored reef denizen… coral slime. 

    In this study Wild et. al examine the coral mucus output of Acropora corals at Australia’s Heron Island measuring the physical release, make up and resulting bacteria growth. They found that Acropora species on the reef can emit up to 4.8l of pure coral mucus per meter squared of reef. Imagine 2 overflowing large soda bottles filled with coral slime! The study specifies the mucus collected was from A. millepora, A. pulchra, A.nobilis and A. aspera. 

    So why am I interested in coral mucus? It may be largely irrelevant in captivity, but the role coral mucus plays in the ocean is rather fascinating. Coral mucus is a nutrient rich excrete containing carbon, nitrogen and phosphorus. In this mucus, bacteria populations have been found to be 100 times greater than surrounding areas. The increased bacteria densities from the mucus then play a role in oxygen levels depleting them relative to surrounding seawater and eventually the sand / sediment where it settles. It goes something like this: Coral releases slime. Slime traps particulate matter. Slime feeds bacteria. Bacteria uses oxygen. Slime and bacteria mix and mingle with plankton. Bacteria laden slime settles to lagoon sediment. Again consumed by bacteria.

    Of the 4.8l of coral slime mentioned previously, Wild et. al found it to contain 10-21 mmol of Particulate Organic Carbon ‘POC’  with 1.5-1.8mmol nitrogen and 0.08-0.18mmol phosphorus. The study states a C:N:P ratio of 72:6:1. This is quite different from the often cited Redfield Ratio of 106:16:1. However, this really does not mean a thing.

    • The Redfield Ratio is for phytoplankton
    • Its largely meaningless for aquarists

    I mention it only as a range and reference from early aquarium carbon dosing discussions. It may prove to be a rough guideline for aquarists in the future, but the testing needed is out of reach for the overwhelming majority of aquarists. That is unless you are Ken Feldman and Kelly Maers. These two released an interesting series of articles on Total Organic Carbon in the aquarium that I would encourage you to read. From it they clearly outline the basics of carbon utilization via photosynthesis and eventual release in corals. It is much more complete than my fragmented description above:

    Photosynthesis utilizes the sunlight’s energy to “fix” (= attach) inorganic carbon in the form of CO2 to organic chemical structures that eventually become carbohydrates. These carbohydrate building blocks are chemically manipulated further by the zooxanthellae and/or the coral host and then secreted by the coral as coral mucus (a combination of complex polysaccharides, amino acid oligomers/polymers, lipids, etc.. The carbohydrates and amino acids within the mucus serve as food sources for the bacteria and other microbiota that comprise the foundation of the marine food pyramid (Kirchman, 1990; Rich, 1996; Weiss, 1999; Wild, 2004; Sharon, 2008).

    Note : the Wild 2004 citation they include. For one reason or another I passed this up. Ken and Kelly’s results matched those of Wild and they found organic carbon levels to rise after feeding the corals like Ferrier-Pagès previously noted.

    Coral slime, who would have thought it could play such a role? The idea of inducing coral mucus in captivity is nothing new. Many of hypothesized the benefits of low tide simulation. Other have even integrated air injection systems to stimulate mucus production.  Corals can release up to half their carbon that is assimilated via zooxanthellae, via mucus. This large percentage and the role coral slime can potentially play in nutrient recycling leaves me in awe of nature and wondering how similar diversity and food chains can be mimicked in home aquaria. 

     

    Wild, C.; Huettel, M.; Klueter, A.; Kremb, S. G.; Rasheed, M. Y. M.; Jergensen, B. B. 2004. “Coral Mucus Functions as an Energy Carrier and Particle Trap in the Reef Ecosystem.” Nature

    [ cover photo : pierre ]

    5 Comments

    1. August 7, 2009 at 12:11 AM | Permalink

      Great read!

    2. August 7, 2009 at 3:04 AM | Permalink

      Excellent post!

      Coral mucus is very important part of coral reef ecology and the number of bacteria in mucus loaded “regenerative” sediments is absolutely amazing, higher than anywhere else in nature. I don’t think it is irrelevant at all in captivity 😉

      BTW, this is something I have also wanted to write about 🙂

    3. stunreefer
      August 7, 2009 at 9:28 AM | Permalink

      If we can synthesize coral mucus in captivity, we can unlock so many doors into the world of non-photosynthetic coral like Scleronepthya and Dendronepthya species. Imagine using a dosing pump to dose coral slime as a food source!

    4. August 7, 2009 at 9:36 AM | Permalink

      Fauna Marin’s UltraPac food comes to mind…

    5. Nicholas Sadaka
      August 9, 2009 at 1:01 PM | Permalink

      Very interesting. No doubt nature has science beat by a good deal in aquatics at this point in time. It seems like the reef is such a perfect and efficient growing ground for its denizens that it really shows the extent of damage that man has done to overcome those perfect conditions and destroy some of these fertile areas. If we could just get them back to those perfect conditions they’d be such an endless source of resources for so many differnt things. The reefs and oceans are such an incredible tool for the health of the world.

    2 Trackbacks

    1. […] SPS Reef in HD Entry Coral Mucus, The Unappreciated Slime Interesting post over at GBD: Coral Mucus, The Unappreciated Slime of Saltwater | glassbox-design.com I have been injecting air into my powerheads at night for several months when I had read a post on […]

    2. […] study estimates that 20% of DOC found on the reefs is the result of expelled coral mucus.  This  coral slime helps drive the food web, feeding bacteria which are then consumed and consumed again. A missing […]

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