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Variation of fucoid community metabolism during the tidal cycle: Insights from in situ measurements of seasonal carbon fluxes during emersion and immersion
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Edité par CCSD ; Association for the Sciences of Limnology and Oceanography -
International audience. Intertidal communities dominated by canopy-forming brown seaweed are typically highly productive sys-tems. However, their metabolism can vary significantly over time, due to fluctuations in abiotic parameters.If tidal and/or seasonal cycles play an important role in the regulation of metabolism in these communities,they may therefore strongly influence community functioning and dynamics. Here, we investigated the lowmid-intertidalFucus serratuscommunity, measuring in situ carbon fluxes of its primary production and respi-ration during different seasons. To perform direct comparisons of its underwater and aerial metabolism, thesemeasurements were carried out during immersion and emersion, analyzing the changes in dissolved inorgan-ic carbon and in CO2concentrations under closed benthic chambers. Our results showed that during bothemersion and immersion periods, primary production and respiration varied seasonally with minimum val-ues in winter and maximum values in summer. These values were, on average, 5 and 3.5 times higher whenthe community was exposed to air than when immersed, due to the large changes that occur in abiotic envi-ronmental conditions during the tidal cycle. Primary production fluctuated greatly during immersion andwas generally limited by underwater light availability. In contrast, primary production remained high duringemersion, partly because canopies limit the water loss of their understory layers. During both tidal periods,community respiration was mainly driven by temperature. Our results suggest that the relatively high metab-olism during emersion contributes substantially to the total energy budget of fucoid mid-intertidal communi-ties, even those that are low on the shore and spend most of their time underwater
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