Photosynthetic capacities and photosynthetic action spectra of endozoic algae of the massive coral Favia

1. The living part of the massive coral Favia is inhabited by a symbiotic dinoflagellate (Zooxanthellae) which resembles Symbiodinium microadriaticum. Intensity/response curves for this alga show that saturation occurred at 95,000 erg. cm.-2 sec-1 in blue light (440 nm). Action spectrum determinations were performed either with an automatic field instrument, or by a point method. The results are mainly as to be expected for a dinoflagellate. A high activity band was noticeable around 540 nm. A similar band was also visible in the in vivo excitation spectrum of fluorescence, as well as in the in vivo absorption spectrum (Shibata, unpublished data).

2. A green alga Ostreobium (Siphonales) can live and photosynthesize within the massive coral. The light levels within the coral are very low; however, wave-lengths above 700 nm are preferentially transmitted by the living part of the coral with the zooxanthellae. Ostreobium showed saturation at or below 1000 erg. cm.-2 sec1 at 440 nm. Some samples showed photooxidation at all light intensities. It was shown that the position of Ostreobium within the coral was decisive for its response to light. Action spectra determinations and in vivo spectrophotometric analyses showed that Ostreobium was adapted to the particular light conditions within Favia in that a pigment, presumably a chlorophyll a form with absorption maximum at 720 nm(Ca720) actively participated in photosynthesis. The effect at 720 nm was up to 80% of the effect at 680. Enhancement studies at 675 and 720 nm gave positive results.