Relationships between primary production and ii radiance in coral reef algal communities1

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Abstract
Shallow water algal turf communities are the major primary producers on coral reefs. High rates of primary production are maintained despite extremely high light intensities and exposure to ultraviolet wavelengths. The relationships between the light intensity and primary production in these assemblages are typical of algae adapted to a high light environment [low α (initial slope), high Ik (saturating light intensity), and high Ic (compensation point light intensity)]. Seasonal variations in algal standing crop due to herbivory and daylength result in some characteristic photoadaptive changes in a, Ik, and Ic, and changes in Pnetmax rate s (maximum net photosynthetic rate achieved at light saturation) on both a chlorophyll a and an areal basis. Exposure to UV wavelengths results in significantly higher respiration rates but no changes in α, Pnetmax, or Ik, when compared with these parameters for the same algal communities incubated at the same light intensities without UV wavelengths. The apparent lack of photoinhibition in these algae allows calculation of the daily integrated production from the P vs. I parameters. This integrated production is highest in July (3.1 ± 0.2 g C m−2 d−1) and is reduced by 30% from this maximum in December (2.1 ± 0.1 g C m−2 d−1).