ECOPHYSIOLOGY OF TROPICAL RHODOPHYTES. I. MICROSCALE ACCLIMATION IN PIGMENTATION1,2

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Abstract
Microscale pigment adjustments to a tropical photosynthetically active radiation and ultraviolet (UV) environment by the intertidal turf algae Ahnfeltiopsis concinna (J. Ag.) Silva et DeCew and Laurencia mcdermidiae (J. Ag) Abbott were promoted by thalli densities that self‐shade the under story portions of the same diminutive axes. Tissues of A. concinna from canopy microsites had significantly reduced levels of phycoerythrin, phycocyanin, and allophycocyanin compared to tissues from understory microsites of the same axes. Tissues of L. mcdermidiae from canopy microsites had reduced levels of only phycoerythrin compared to tissues from understory microsites. These alterations coupled with enhanced levels of carotenoid and UV‐absorbing compounds in tissues from canopy compared to tissues from understory microsites indicated a pattern of remarkably sensitive photoacclimation over the ≤10‐cm axes of these turf‐forming rhodophytes.Microscale variation in the in vivo UV absorbance capabilities for turfs of A. concinna and L. mcdermidiae was directly related to the amount of extractable UV‐absorbing compounds. An in vivo absorbance signature at ∼345 nm appears to provide a method to quickly and accurately gauge the potential UV‐shielding capacity of primary producers even at remarkably fine ecological scales. The capacity for highly responsive biochemical adjustments that result in marked canopy–understory distinctions coupled with a turf morphology may be crucial for macroalgal tolerance of physiological stresses associated with tropical intertidal zones. This responsive capacity allows for enhanced photoprotective mechanisms in tissues from canopy microsites while optimizing irradiance capture in deeply shaded tissues from understory microsites < 10 cm away.