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Photosynthetic activity was estimated, in 2 different sets of experiments, as in vivo chlorophyll a fluorescence in 2 calcareous red macroalgae: Neogoniolithon brassica-florida, which forms vermetid reefs with Dendropoma petraeum, and the rhodolith-forming Lithophyllum margaritae. In the first set of experiments, vermetid reefs collected from the Cabo de Gata-Níjar Natural Park (Almería, Spain) were incubated for 6 months in outdoor mesocosms at 2 different temperatures: ambient temperature (T) and ambient temperature plus 2 ºC (T+). Daily variations in effective quantum yields were related to the increase in solar radiation. Electron transport rate (ETR) was higher at T+ than at T. Oxygen production, estimated from ETR, was higher in N. brassica-florida growing in vermetid reefs in the coastal area than in those incubated in mesocosms or under laboratory conditions. In the second set of experiments, L. margaritae specimens with or without attached epifauna (mainly sponges) were collected at 2 sites (Pedregoso and CFE) on the Baja California Peninsula, Mexico, and at 2 depths (1 and 2 m). ETR values for rhodoliths collected at 1 m depth and with attached epifauna were higher than those for rhodoliths collected at 2 m depth, indicating the importance of greater incident radiation on photosynthetic activity. Photosynthetic activity was higher in L. margaritae collected from Pedregoso, the site with better water quality (high transparency and low pollution) and rocky substrate availability. In the CFE samples, the photosynthetic efficiency (alphaETR) was highest in rhodoliths with attached epifauna. The highest ETR values for N. brassica-florida at T+ and the highest alphaETR or ETR values for L. margaritae with attached sponges may be explained by the increase in CO2 available for photosynthesis due to the respiration of the associated fauna. The usefulness of in vivo chlorophyll a fluorescence for estimating photosynthetic production in calcareous macroalgae under multifactorial experiments is discussed.
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