ChrisRD":1s1mth2e said:
DaisyPolyp":1s1mth2e said:
Actually, the quote was that the 400-520 range is most effective in eliciting tentacle retraction (a function of the coral's tissue), I stated before that 440-480 was the most important in coral photosynthesis (a function of the zooxanthellae). The coral doesn't want to get in the way of the light needed for the zooxanthellae, so it contracts before the optimal time and expands after the optimal time. referencing back to the chart you see that 400nm and 520nm are not anywhere near the peak spectrum shown for photosynthesis.
Corals in reef tanks that are poorly lit will generally over-extend their polyps in an effort to get
more light. They will generally show
less extension under higher lighting intensities (at least until they acclimate to those conditions)...
This is a complete misinterpretation of coral behavior.
1. Coral in a low-light tank over extend their polyps because they're trying to get more planktonic food to supplement the lack of energy derived from the photosynthesis process.
2.
This statement makes no sense. The zooxanthellae are inside the coral's tissue... ...how would retracting the polyps help in attaining light energy?
Most reef corals expand their tentacles only at night (Lewis and Price, 1975; Porter, 1974)
a beam of light or mechanical stimulation can cause nocturnally expanded tentacles to contract immediately (Abe, 1939).
zooplankton is most abundant on coral reefs during the night (Sorokin, 1990).
On the coral reef at Eilat, in the northern
Red Sea, the massive stony corals
Favia favus and
Plerogyra sinuosa expand their tentacles nocturnally and contract them at sunrise (O.Levy et. al, 2003).
daytime expansion of tentacles[...]may lead to an overall decrease in the photosynthetic rate, due to light scattering (Pearse, 1974; Robbins and Shick, 1980; Lasker, 1981).
in
Acropora acuminata the light saturation level and the compensation point were 25% higher when polyps were contracted than when they were partially expanded (Crossland and Barnes, 1977)
(I will note that there are exceptions, namely within the genus Gonipora, because their tenticles have extremely high zooxanthellae densities)
References:
Lewis, J. B. and Price, W. S. (1975). Feeding mechanisms and feeding
strategies of Atlantic reef corals. J. Zool. 176, 527-544.
Porter, J. (1974). Zooplankton feeding by the Caribbean reef-building coral
Montastrea cavernosa. Proc. 2nd Int. Coral Reef Symp. 1, 111-125.
Brisbane, Australia: Great Barrier Reef Committee.
Abe, N. (1939). On the expansion and contraction of the polyp of a coral reef
Caulastrea furcata Dana. Palao. Trop. Biol. Stn. Stud. 1, 651-670.
Sorokin, Y. I. (1990). Plankton in the reef ecosystems. In Ecosystems of
the World, Coral Reef (ed. Z. Dubinsky), pp. 291-327. Amsterdam:
Elsevier.
O. Levy, Z. Dubinsky and Y. Achituv (2003). Photobehavior of stony
corals: responses to light spectra and intensity
The Journal of Experimental Biology 206, 4041-4049
Pearse, V. B. (1974). Modification of sea anemone behavior by symbiotic
zooxanthellae: Expansion and contraction. Biol. Bull. 147, 641-651.
Robbins, R. E. and Shick, J. M. (1980). Expansion–contraction behavior in
the sea anemone Metridium senile: Environmental clues and energetic
consequences. In Nutrition in the Lower Metazoa (ed. D. C. Smith and Y.
Tiffon), pp. 101-116. New York: Pergamon.
Lasker, H. R. (1981). Phenotypic variation in the coral Montastrea cavernosa
and its effects on colony energetics. Biol. Bull. 160, 292-302.
Crossland, C. J. and Barnes, D. J. (1977). Gas-exchange studies with staghorn
coral Acropora acuminata and its zooxanthellae. Mar. Biol. 40, 185-194.
...just in case you want to look it up. :wink:
