Effects of elevated CO2 and nutrients on the community metabolism of a Cymodocea nodosa bed

Authors: FAISAL KHAN, ANA ALEXANDRE, HADAYET ULLAH, RUI SANTOS

Abstract: We assessed the combined effects of elevated CO₂ and nutrients on the metabolism of a benthic community dominated by the seagrass Cymodocea nodosa (Ucria) Ascherson in a mesocosm experiment. C. Nodosa plants and their associated community were exposed to two CO₂ levels simulating future (700 ppm, pH 7.84) and current (360 ppm, pH 8.12) conditions, and two nutrient levels (enriched and ambient concentration) in a total of four treatments (-C-N, -C+N, +C-N, +C+N). Net community production (NCP) was estimated from changes in the concentration of dissolved inorganic carbon in the seawater in light incubations using benthic chambers. The variation pattern of NCP with the ordinance was consistent for all treatments. Although differences among treatments were not statistically significant, average NCP values were lowest under CO₂ enrichment conditions. NCP was lower at a high CO₂ level and ambient nitrogen concentration compared to when nutrient availability was higher, suggesting that the low nutrient availability may modulate the community response to CO₂ enrichment. The results obtained suggest that the stimulation of the net community production of C. Nodosa by elevated CO₂ concentrations may be curtailed by low nutrient availability.

Keywords: CO₂ enrichment, net community production, nutrients, seagrass

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