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Photobehavior of SPS and reason for polyp extension

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  • Photobehavior of SPS and reason for polyp extension

    Read below. Denser or shorter (by species) tentacles of zooxanthallae are usually the corals that always show polyp extension and the stronger light intensity (short wavelengths - 10K-6.5K) contract these polyps. In other words, too much light will decrease polyp extension. Is this true for more clear water (low nutrient) too?


    O. Levy*, Z. Dubinsky and Y. Achituv

    Faculty of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel

    Accepted 22 July 2003

    Tentacle expansion and contraction were investigated in four zooxanthellate coral species and one azooxanthellate coral (Cladopsammia gracilis). Favia favus, Plerogyra sinuosa and Cladopsammia gracilis expand their tentacles at night, while tentacles in Goniopora lobata and Stylophora pistillata are expanded continuously. Light at wavelengths in the range 400-520 nm was most effective in eliciting full tentacle contraction in F. favus and in P. sinuosa. Higher light intensities in the range 660-700 nm also caused tentacle contractions in F. favus. Tentacles in C. gracilis did not respond to light. Zooxanthellar densities in tentacles were significantly higher in G. lobata, which has continuously expanded tentacles, than in F. favus and P. sinousa, where tentacles are expanded at night. Photosynthetic efficiency in F. favus and P. sinuosa was lower in specimens with contracted tentacles. However, in the dark, no differences were found in the maximum quantum yield of photochemistry in PSII (Fv/Fm) of the expanded versus the contracted tentacles of any of the four species. This work suggests that species whose tentacles remain continuously expanded have either dense algal populations in their tentacles, as in G. lobata, or minute tentacles, like S. pistillata. Dense algal populations in tentacles allow harvesting of light while small tentacles do not scatter light or shade zooxanthellae in the underlying body of the polyp.

  • #2
    Greetings All !

    Great find, Edward! ...

    For anyone interested in the full text ...
    Photobehavior of stony corals: responses to light spectra and intensity
    </NOBR><NOBR>(O. Levy</NOBR>, <NOBR>Z. Dubinsky</NOBR> and <NOBR>Y. Achituv, 2003)</NOBR>

    In other words, too much light will decrease polyp extension. Is this true for more clear water (low nutrient) too?
    Hardly surprising ... just another aspect of "photoinhibition" mechanisms. As "clearer water" facilitates the transmission of a higher light intensity to a greater depth ... less attenuation ("scattering") ... it could be factor.

    My twisted little mind found some of the following rather interesting ...

    "We suggest that differences in algae density and their distribution<SUP> </SUP>within the tissue may lead to differences in the relative contribution<SUP> </SUP>of their energy sources. The relative importance of autotrophy<SUP> </SUP>versus heterotrophy in a given species can be reflected in the<SUP> </SUP>diel behavioral patterns of tentacle expansion and contraction.<SUP> </SUP>Levy et al. (2001) showed that polyps of Favia favus could be<SUP> </SUP>induced to expand under high flow velocity and low-medium light<SUP> </SUP>(below the compensation point), regardless of the presence of prey.<SUP> </SUP>Thus in corals with a low density of zooxanthellae in their<SUP> </SUP>tentacles there is a hierarchy of responses, with light level<SUP> </SUP>and flow speed overruling the presence of prey. These results<SUP> </SUP>probably do not apply to corals that contain high algal densities<SUP> </SUP>in their tentacles (such as G. lobata), which would benefit<SUP> </SUP>from expansion whenever light levels are high."

    ... [and] ...

    "Our results on the effect of light spectrum on tentacle contraction behavior<SUP> </SUP>in F. favus and P. sinuosa, and the absence of this effect in<SUP> </SUP>azooxanthellate corals, support the notion that this behavior<SUP> </SUP>is related to the photosynthetic activity of the zooxanthellae."

    ... [and] ...

    "Our results seems to point to a causative relationship between<SUP> </SUP>the photosynthesis of the zooxanthellae (or the products thereof)<SUP> </SUP>and tentacle behavior in corals, but cannot totally exclude<SUP> </SUP>the possibility that such cells are sensitive to the same wavelengths<SUP> </SUP>as the photosynthesis, and may also play a role in coral behavior.<SUP> "</SUP>
    <SUP>Extracted from above referenced article.</SUP>
    <SUP>Very cool stuff ... </SUP>
    "When the going gets weird, the weird turn pro."
    Hunter S. Thompson


    • #3
      Wow, didnt even see the full article!

      I also forgot about flow. That definitely plays a major role. They even went as far as measuring the polyps with this formula. SWEET!

      where SA is tentacle surface area, r is the tentacle radius and h is tentacle length.


      • #4
        so then we would get better extension wit higher temp bulbs and more flow ?
        180G SPS Mainly
        10 Bulb T5 Starfire
        Calcium Reactor
        3 Tunze 6105's
        Profilux Controller
        ATB Return w/ wavysea
        ATB M External Skimmer