deep water coral

Photoadaptations of zooxanthellae living with- in the deep water coral Leptoserisfragilis taken from the Gulf of Aqaba (Red Sea) were studied. Specimens - col- lected in summer 1988 between 110 and 120 m depth - were transplanted to 70 and 160 m. At each depth indi- viduals were exposed in their natural growth position (oral side facing the surface) or in a reverse growth posi- tion (oral side facing the bottom). After 1 yr of exposure the corals were collected and the zooxanthellae were iso- lated. As a function of the availability of light with depth and growth position several algal parameters showed changes which are related to photoadaptations. The rela- tively low density of zooxanthellae of 0.15 x 106 cells x cm -2 at a natural growth depth of 116 m de- creased to 0.0034 x 106 cells x cm -2 (A2%) at 160 m in specimens growing with a natural orientation. In corals with a downward-facing oral surface at the same depth (160 m) only degenerated algae could be observed. With respect to depth dependence the volume of the algae de- creased from 728 ixm 3 at 116 m to 406 ~tm 3 at a depth of 160 m and the content of pigments increased. The aug- mentation of peridinin per cell was low (two times at 160 m compared to 116 m). Chlorophyll a and in particu- lar chlorophyll c2 concentrations per cell were enhanced. Compared to natural amounts at 116 m, chl a was five times and chl c2 eight times higher at 160 m. At all depths the chl c 2 content per cell was higher than for chl a. The formation of chl a/chl c 2 complexes as light harvestor is discussed. Light harvesting, with chl c2 prevailing may be explained as a special type of chromatic adaptation of L. fragilis in a double sense: (1) in the habitat light short wavelengths predominate. This light can be directly ab- sorbed with pigments such as chl a and chl c2. (2) Host pigments absorb visible violet light and transform these wavelengths, less suitable for photosynthesis, into longer ones by means of autofluorescence. The emitted longer wavelengths fit the absorption maxima of the algal pig- ments. Thus the host supports photosynthesis of his sym- bionts. Corals exposed at 160 m depth with a downward

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