Estimation of photosynthesis and calcification rates of &lt;i&gt;Corallina elongata&lt;/i&gt; Ellis and Solander, 1786, by measurements of dissolved oxygen, pH and total alkalinity

Bouazza El Haïkali,Jean Claude Romano,Vincent Bousquet,Nathaniel Bensoussan

doi:10.3989/scimar.2004.68n145

Abstract

Experiments were conducted on the calcareous red alga, Corallina elongata, a species representative of shallow water vegetal cover in Mediterranean areas with biomass ranging from 820 to 2544 gDW.m-2, in order to estimate its productivity and calcification rates. Carbonate and oxygen budgets were estimated on samples incubated in situ under natural light cycles, by measuring initial and final dissolved oxygen, pH and alkalinity levels. In light conditions, oxygen concentrations and pH values increased as a consequence of oxygen production and carbon dioxide consumption due to the productivity process, and were a direct function of sample biomass. Strictly-reverse dynamics were recorded in dark conditions. A comparison of photosynthetic performances was conducted on a non-calcareous green alga, Ulva rigida, which showed higher rates of oxygen production and pH modification than C. elongata, but no significant change in total alkalinity. For C. elongata, a significant decrease in total alkalinity with incubation time was observed under light conditions, which was directly related to the algal sample biomass (R2 = 0.95; n=16). Light to dark calcification ratio (L/D) was about 3.6. In these experiments, the photosynthetic quotient of C. elongata was 0.89, its net carbon productivity was 2.5 g C.m-2.d-1, gross production to daily respiration (Pg/R) was about 4.9 and its calcification rate was estimated at 13.8 g CaCO3.m-2.d-1.

Highlights

Calcification process studies in calcareous macroalgae are recent and mainly focus on coralreef ecosystems which are the most striking example of calcifying ecosystems (Gattuso et al., 1999)
We present the evolution of dissolved oxygen, pH and total alkalinity during dark or light in-situ incubation experiments of a calcareous C. elongata collected in the shallow waters of the Marseilles area, in relation to the biomass employed for the experiment
In order to express photosynthetic activities in milligrams of carbon, we calculated photosynthetic quotients according to the following method: The total CO2 change or dTCO2 (TCO2: the sum of CO2, H2CO3, HCO3- and CO32-) in the incubation flask is the sum of total inorganic carbon changes due to calcification and to photosynthesis/respiration

Summary

Introduction

Calcification process studies in calcareous macroalgae are recent and mainly focus on coralreef ecosystems which are the most striking example of calcifying ecosystems (Gattuso et al., 1999). In the northwestern Mediterranean Sea, recent research (Canals and Ballesteros 1997; Massé 1999; Cebrián et al, 2000) has studied coastal benthic ecosystems with a relatively high carbonate content and high carbonate production. Photosynthetic and respiratory activities of marine organisms have an impact on the sea water content of various compounds such as oxygen, CO2 and carbonate ionic forms (Smith and Key, 1975; Sournia 1982) Among the latter, bicarbonate ions (HCO3-) may be used as a potential carbon source for photosynthetic processes (Larkum et al, 1989; Johnston et al, 1992; Bjôrk et al., 1992). In most cases, it is considered that in the natural environment photosynthetic and respiratory budgets do not change TA values due to the CaCO3 oversaturation situation in surface waters (Sournia, 1982; Copin-Montégut, 1996)

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Conclusion