ABSTRACT: In situ diel patterns of productivity, total daily productivity (¹⁴C-uptake) and microphytobenthic biomass were measured at 3 sites from different tidal regimes: a shallow subtidal site with negligible tidal fluctuations (Sweden), a shallow subtidal site exposed to distinct salinity and turbidity variations (Italy) and an intertidal site in a macrotidal estuary (Portugal). Measurements were taken at regular intervals (5 to 7) throughout the period that the sediment was light-exposed and replicated over 3 d. The pattern of diel productivity varied between the sites. The subtidal Swedish site showed the clearest pattern, closely following daily irradiance, while productivity at the Italian subtidal site was influenced by varying freshwater input affecting the turbidity. Daily productivity at the intertidal site was controlled mainly by the tidal exposure patterns, but changes in rates of productivity also occurred across the emersion period. This variation could not be explained purely by irradiance, suggesting the influence of further factors, e. g. nutrient limitation. Despite different sediment type, tidal amplitude and species composition, the biomass and total daily primary productivity at the sites was of the same order of magnitude, suggesting a similar carrying capacity. The main difference between the sites was in the degree of intra-site variation, being greatest for the intertidal site. The relationship between in situ productivity (measured across the diel cycle) and irradiance varied between sites. No relationship could be determined for the highly motile intertidal microphytobenthic community, while a statistically significant relationship between in situ microphytobenthic productivity and irradiance was found at the 2 subtidal sites.

KEY WORDS: Primary productivity · Diel variation · Tidal amplitude · Microphytobenthos · Sediments

Full text in pdf format

Published in MEPS Vol. 205 (2000) on October 19
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000