Carbon isotopic fractionation in macroalgae from Cádiz Bay (Southern Spain): comparison with other bio-geographic regions

Mercado, Jesús M.; de los Santos, Carmen B.; Pérez-Lloréns, J. Lucas; Vergara, Juan J.

http://hdl.handle.net/10400.1/17627

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Authors

Mercado, Jesús M.

de los Santos, Carmen B.

Pérez-Lloréns, J. Lucas

Vergara, Juan J.

Abstract(s)

The 13C signature of forty-five macroalgal species from intertidal zones at Ca´diz Bay was analysed in order to research the extension of diffusive vs. non-diffusive utilisation of dissolved inorganic carbon (DIC) and to perform a comparison with data published for other bio-geographic regions. The v13C values ranged from !6.8& to !33&, although the span of variation was different depending on the taxa. Thus, v13C for Chlorophyta varied from !7& (Codium adhaerens) to !29.6& (Flabellia petiolata), while all the Phaeophyceae (excepting Padina pavonica with v13C higher than !10&) had values between !10&, and !20&. The widest variation range was recorded in Rhodophyta, from values above !10& (Liagora viscida) to values lower than !30& obtained in three species belonging to the subclass Rhodymeniophycidae. Accordingly, the mean v13C value calculated for red algae (!20.2&) was significantly lower than that for brown (!15.9&) and green algae (!15.6&). Most of the analysed red algae were species inhabiting crevices and the low intertidal fringe which explains that, on average, the shaded-habitat species had a v13C value lower than those growing fully exposed to sun (i.e. in rockpools or at the upper intertidal zone). The comparison between the capacity for non-diffusive use of DIC (i.e. active or facilitated transport of HCO3 ! and/or CO2) and the v13C values reveals that values more negative than !30& indicate that photosynthesis is dependent on CO2 diffusive entry, whereas values above this threshold would not indicate necessary the operation of a non-diffusive DIC transport mechanism. Furthermore, external carbonic anhydrase activity (extCA) and v13C values were negatively correlated indicating that the higher the dependence of the photosynthesis on the CO2 supplied from HCO3 ! via extCA, the lower the v13C in the algal material. The comparison between the v13C values obtained for the analysed species and those published for species inhabiting other bio-geographic areas (warm-temperate, cold and polar) suggests that globally (at least for the red and brown algae) the non-diffusive entry of DIC is more widely spread among the species from Ca´diz Bay than among those of polar regions. If it is assumed that nondiffusive use of DIC implies saturation of photosynthesis at the present-day CO2 concentration in seawater, our data indicate that the potential impact of the acidification on photosynthesis in the seaweed communities will be different depending on the latitude.