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closeCoral Color: Evolutionary Pressure to be Unique on the Reef
Posted by bowdenkerby on 20 Aug 2009 at 09:35 GMT
Lets back up and look at thye broader picture: not only do corals have such diverse interspecific color variation, so do giant clams, spirobranchus "christmas tree" worms, etc... Why? it may not all about light capture or internal physiology... but may be related more to predation and competition, in this case fighting for planktonivorous fish... yes the coral are fighting for the fish- especially the blue Chromis and humbug damsels! These fish help the corals grow and reproduce. HMy hypothesis is that the brightest or most differently colored coral tends to get more fish, as it is in their advantage to chose a distinct colony to rapidly get back inside when in danger. We also have reef sites here where parrotfish kill out most of the corals... where people remove all the brightly colored giant clams, but the brown ones escape. All sorts of reasons to be differently clored on the reef. The visual system of fish could be looked at- which are they more or less sensitive to florescent proteins-parrotfish vs groupers for example. Unfortunately we have found that most of the highly colored corals are killed out by thermal stress and bleaching, while the duller colored ones tend to survive... so this does indicate that the proteins may be increasing available light- acting as accesory pigments during low light conditions at dawn, dusk, and during the MANY cloudy days of the rainy tropics. We have great research sites here in Fiji and we have farmed corals of incredible colors... multple colonies of each gemnotype for experimentation. Did you see our corals growing on Discovery Channel Wild Pacific in July?
RE: Coral Color: Evolutionary Pressure to be Unique on the Reef
c-mnstr replied to bowdenkerby on 20 Aug 2009 at 18:45 GMT
Dear Austin,
That coral color may be relevant for coral-fish ecological interaction, ultimately leading to higher fitness of both fish and coral, is an extremely attractive idea. Bill Ward was one of the first who published thoughts along these lines (Ward, W. W. (2002) Fluorescent proteins: who’s got ’em and why? In Bioluminescence and Chemiluminescence (Edited by P. E. Stanley and L. J. Kricka), pp. 22–24. World Scientific Publishers, Singapore). The idea is, however, extremely difficult to test. All we have done so far is modeling whether fish could discriminate coral colors based on their visual capabilities – looks like they can (Matz, M. V., Marshall, N. J. and Vorobyev, M. Are corals colorful? Photochem. Photobiol., 2006, 82: 345-350. PMID: 16613484). I am not aware of any studies taking this further. Fish could see the colors, but do they care? The logical next step would be, as you suggest, to check whether fish respond to coral colors on the reef, perhaps using the colors as navigation landmarks – this is actually a very nice idea of yours, and it feels like it is possible to devise an appropriate experiment.
I am intrigued by your statement that fish help the coral grow and reproduce. I would love to see the data. Can you please elaborate? Perhaps point me to the appropriate references?
Another unexpected piece of news for me was that the brightly colored corals are preferentially killed by stress and bleaching. This goes against the currently prevailing view that fluorescent morphs are actually more resistant to heat-light induced stress (Salih, A., A. Larkum, G. Cox, M. Kuhl and O. Hoegh-Guldberg (2000) Fluorescent pigments in corals are photoprotective. Nature 408, 850–853.) Again, I would greatly appreciate some additional info on this subject!
Cheers
Misha
RE: RE: Coral Color: Evolutionary Pressure to be Unique on the Reef
bowdenkerby replied to c-mnstr on 25 Aug 2009 at 12:11 GMT
Hi Misha,
Thanks for your positive reply and for not complaining about my typos or lack of references! The bit below is copied from my PhD thesis, I can send you the pdf file of the entire chapter if you email me. bowdenkerby@yahoo.com
In the severe bleaching of 2000 here in Fiji at the Cuvu coral coast site all of the bright pinkish colored Pocilloporas and Styloporas on the reef flat died out, leaving only brown colored ones. The yellows and blues mostly did okay, the browns fared the best (A. Bowden-Kerby personal observations for Yanuca Cuvu Fiji). The same thing happens when we move pink corals from the reef to the reef flat. Obviously we need more quantitative data, but this is what we have observed many times.
Austin
The Effect of Fish on Coral Growth
A positive relationship has been established between fish abundance within branching coral colonies and the growth of these corals (Meyer et al., 1983; Meyer and Schultz, 1985a,b; Liberman, 1991). Coral growth is presumably stimulated by excretion of fish living within the coral branches in otherwise nutrient poor, oligotrophic waters of coral reefs (Meyer et al., 1983; Meyer and Schultz, 1985a,b; Liberman, 1991). The establishment and growth of transplanted corals may thus be influenced by the presence of fish, with a potentially mutualistic relationship between corals and their fish recruits.
Liberman, T. 1991. The association between the coral Stylophora pistillata and the damselfish Dascyllus marginatus: possible advantages to the coral. MS Thesis in Zoology, Tel Aviv Univ. 81pp
Meyer, J.L. and Schultz, E.T. 1985a. Migrating haemulid fishes as a source of nutrients and organic matter on coral reefs. Limnol. Oceanogr. 30: 146-156
Meyer, J.L. and Schultz, E.T. 1985b. Tissue condition and growth rate of corals associated with schooling fish. Limnol. Oceanogr. 30: 157-166
Meyer, J.L., Schultz, E.T. and Helfman, G.S. 1983. Fish schools: an asset to corals. Science 20:1047-1049
RE: RE: RE: Coral Color: Evolutionary Pressure to be Unique on the Reef
bowdenkerby replied to bowdenkerby on 25 Aug 2009 at 12:19 GMT
PS. My Thesis showed a highly significant negative correlation between fish numbers adn coral growth in La Parquera PR. It seems that the waters are already near the nutrient threshold for inhibiting coral growth and so it appears that the fish urine puts them over the threshold and begins inhibition.
Bowden-Kerby, W. A. 2001. Coral transplantation modeled after natural fragmentation processes: Low-tech tools for coral reef restoration and management. PhD Thesis, University of Puerto Rico at Mayaguez 195 pp.