Abstract
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.
Highlights
Among macroalgae, the Rhodophyta constitute the group with the highest diversity in the sea
Specimens of N. brassica-florida associated with vermetid reefs (D. petraeum) were collected from Cabo de Gata-Níjar Natural Park (Almería, Spain: 36o48 N, 2o03 W) (Fig. 1a) and transported in temperature-controlled tanks to the mesocosm system at Malaga University’s Unit for Microbiology, Ecophysiology and Genetics of Aquatic Organisms (UMEGOA)
The ΔF/Fm values obtained for N. brassica-florida forming vermetid reefs and incubated in outdoor mesocosms decreased from the morning to noon and increased from noon to the afternoon (Fig. 4a)
Summary
The Rhodophyta constitute the group with the highest diversity in the sea. Calcareous red algae represent a high proportion of species within the Rhodophyta (Lüning 1990). Coralline algae are an ubiquitous algal group and they are dominant in coral reef communities (Littler 1973, Glynn 1996). Calcareous algae can grow in deep waters (200 m depth) at the limit of the photic zone (0.0015 mol m–2 s–1) and in surface waters exposed to high levels of photosynthetically active radiation (PAR) and ultraviolet (UV) radiation (Littler et al 1991, Payri et al 2001). The primary production of crustose coralline macroalgae is considered high due to their great abundance, the contribution of organic carbon production rate is low (Larkum and Wood 1993). According to Chisholm et al (1990), the organic productivity has been possibly underestimated since most studies on photosynthetic activity have been conducted using artificial light sources
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