ECOPHYSIOLOGY OF TROPICAL RHODOPHYTES. I. MICROSCALE ACCLIMATION IN PIGMENTATION^1,2

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.

Size, survival and the potential for reproduction in transplants of Mazzaella splendens and M. linearis (Rhodophyta)

“…Several factors can lead to algal bleaching and could be responsible for this condition of M. linearis genets in the sheltered transplant site. These include higher irradiance due to lack of shading, potentially lower nitrate levels due to less mixing events during the summer, a disruption of nutrient uptake by higher levels of desiccation, and a thicker blade (Waaland et al 1974, Gerard & Mann 1979, Thomas et al 1987, Gantt 1990, Hurd & Dring 1991, Beach & Smith 1996, Hurd et al 1996. We consider the bleaching of M. linearis to indicate physiological damage, unlike for M. splendens, because M. linearis genets from natural populations do not demonstrate the degree of bleaching demonstrated by M. linearis experimental genets, and bleached individuals of M. linearis in our experiment were more likely to die or lose biomass.…”

Effects on aquatic ecosystems

“…They also differ in their ability to cope with enhanced UV radiation [107]. A broad survey was carried out to understand photosynthesis in aquatic ecosystems and the different adaptation strategies to solar radiation of ecologically important species of green, red and brown algae from the North Sea, Baltic Sea, Mediterranean, Atlantic, polar and tropical oceans [26,106,[108][109][110][111][112][113].…”

“…Since these substances are chemically very stable, they accumulate in the sediment of lakes and can be used of a permanent record for past ultraviolet radiation environments [131]. In tropical algae, enhanced levels of carotenoids and UV-absorbing compounds were detected in tissues from the canopy compared to tissues from understorey locations in turf-forming rhodophytes [110,111]. Current research indicates that solar UV-B is a stress factor for macroalgae and seagrasses even at current levels; therefore further increases in UV-B may reduce biomass production and changes in species composition in macroalgae ecosystems.…”

UV‐acclimation responses in natural populations of cyanobacteria (Calothrix sp.)

“…Research on phytochrome‐mediated shade responses in higher plants has shown that plants acclimated under highly crowded, low‐irradiance conditions display significant stem elongation that confers a fitness advantage in a crowded setting compared with plants acclimated to high‐irradiance conditions where crowding is not a problem (Schmitt et al ., 1995; Dudley and Schmitt, 1996). Similarly, marine micro‐ and macroalgae have been shown to precisely regulate photopigment content in response to changes in irradiance (Goldsborough and Kemp, 1988; Villafañe et al ., 1995; Beach and Smith, 1996a; Beach and Smith, 1996b; Helbling et al ., 1996; Robinson et al ., 1997; Vergara et al ., 1998; Zudaire and Roy, 2001). Many of these studies also found an increase in UV‐absorbing pigments (e.g.…”