Biometrics in Laminaria digitata: a useful tool to assess biomass, carbon and nitrogen contents

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Carbon and nitrogen content of <i>Laminaria saccharina</i> in the eastern English Channel: biometrics and seasonal variations

Fresh weight (FW), dry weight (DW), carbon and nitrogen content were measured for specimens of Laminaria saccharina (Heterokontophyta: Phaeophyceae) sampled in the eastern English Channel in order to conduct a biometrical study. The aim was to relate carbon and nitrogen masses of the algae to a simple and rapid morphological measurement of the total length of the sporophyte. These relationships were highly significant and appeared very useful to express the standing biomass of L. saccharina in terms of carbon or nitrogen and then to consider dynamic processes such as primary production. Variations in tissue carbon (C) and nitrogen (N) were examined over a complete seasonal cycle. Average carbon and nitrogen content ranged from 23·9 to 31·4% and 2·23 to 3·42% of the total dry weight, respectively. Variations in C/N ratio showed a clear seasonal pattern with an increase in the early spring corresponding to strong photosynthesis and growth

Calculation of annual budget of net benthic production in the Mont Saint-Michel Bay with emphasis on the influence of cloudiness, migration of microphytobenthos and variation of the respiration rate with the alternation of emersion-immersion periods

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Annual budget of benthic production in Mont Saint-Michel Bay considering cloudiness, microphytobenthos migration, and variability of respiration rates with tidal conditions

International audienceIn order to provide an accurate annual rate of net benthic community production, community photosynthetic response to incident irradiance and respiration were measured at different times of the year, at mid-tide level on the muddiest part of the Mont Saint-Michel Bay. As the water turbidity prevented any photosynthesis by the microphytobenthos during immersion periods, primary production was measured only during emersion periods. In contrast respiration was expected to vary according to the tidal cycle and was measured during both emersion and immersion periods. Primary production and respiration rates under emersion were assessed using in situ infra-red gas analysis of CO(2) exchange measured in a benthic chamber. Respiration rates under immersion were assessed through total CO(2) concentration variations in incubated cores. When respiration rate was considered constant over a day and equal to the rate measured under emerged conditions, the community respiration was 54.56 gC m(-2) yr(-1). Taking into account the variations of respiration during the emersion/immersion cycle, community respiration increased to 101.76 gC m(-2) yr(-1) (86% increase). Assuming that community primary production varied as a function of irradiance from the time of exposure until flooding, GCP was 53.22 gC m(-2) yr(-1) when calculated with theoretical irradiance and 45.86 gC m(-2) yr(-1) after correction for cloudiness (14% decrease). Then, by integrating the effect of vertical migration of microphytobenthos, the rate was adjusted to 23.49 gC m(-2) yr(-1) (49% decrease). The net community production budget, calculated as the difference between the GCP and the CR budgets taking into account the corrections described above, was -78.27 gC m(-2) yr(-1). This example of annual budget calculation highlights the need to integrate several processes occurring over various time scales to accurately reflect the metabolic balance of a system The results also confirmed the heterotrophic status generally suggested for intertidal muddy sediments. (C) 2009 Elsevier Ltd. All rights reserved

Conditions and diet of larval Pleuragramme antarcticum (Nototheniidae) from Terre Adélie (Antarctica) during summer.

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