AIR-SEA CO2 FLUXES IN MACROALGAL DOMINATED COMMUNITIES

ALFONSO, B.; EPHERRA, L.; HERNÁNDEZ, C.A.; GONZÁLEZ-DELGADO, S.; HERNÁNDEZ, J.C.; RODRÍGUEZ, A.

Szczecin

Congreso; 11th International Phycological Congress; 2017

Journal of the International Phycological Society

The ocean helps mitigate climate change due to its large capacity to store CO2, enabled by the interplay of physical, chemical and biological processes. Ocean CO2 absorption results in the sequestration of 25% of the total emissions from human activity. The contributions of various vegetated systems to this percentage have been intensively studied. However, the sink capacity of benthic macroalgae and its carbon dynamics are largely unknown. In this sense, the aim of this study was to gain a better understanding of the biogeochemical cycle of carbon in macroalgal dominated ecosystems. Community metabolism was investigated using a minimum of two benthic chambers on four rocky reefs at two different marine protected areas off El Hierro Island and La Graciosa islet (Canary Islands, Spain). The chambers consist of plastic domes enclosing a set of O2, CO2, pH and PAR autonomous sensors. Alkalinity was also measured at different times during the 24 h incubation time by extracting seawater from the chambers with syringes. The dynamics of community gross primary production (Pg), respiration (R) and community net calcification (G) were calculated. Then, the daily air-sea CO2 flux (FCO2) was calculated using the formula: FCO2 = -Pg +R+ YG, Y being the ratio of CO2 released to CaCO3 precipitated. The daily FCO2 obtained at contrasting macroalgae systems was significantly different between studied reefs. La Graciosa islet reefs released CO2 (1.52/3.53 mmol C × m-2 × day-1) to the atmosphere while El Hierro island reefs absorbed CO2 (?45.40/?61.22 mmol C × m-2 × day-1). This contrasting ability to absorb CO2 was mainly due to the contrasting dominant macroalgae communities found at each studied area. We believe that the data obtained in this study, as well as the methodology used, is of interest to community ecologist and environmental managers.