In vivo absorbance spectra and the ecophysiology of reef macroalgae

Abstract.

 In vivo absorbance spectra were obtained for 12 species of tropical macroalgae. Absorbance of UV irradiance was greater than absorbance of photosynthetically active radiation in most algal taxa. UV irradiance may be pre-emptively captured by UV absorbing compounds as indicated by the significant relationship between in vivo and extract absorbance characteristics. In vivo and extract absorbance characteristics indicated that concentrations of UV absorbing compounds were highest among rhodophytes. Additionally, a marked consistency was observed in the visible spectral region, 400 to 750 nm, for in vivo absorbance and fourth derivative maxima for species within specific taxonomic divisions. For Gracilaria salicornia, pigment and photosynthetic performance acclimation paralleled the sun to shade irradiance gradient established by its mat-like morphology. Regression relationships of in vivo absorbance for phycoerythrin and carotenoid-specific maxima with I _k , I _c , and P _max were significant and may have utility in modeling algal photosynthetic parameters.