Depth distribution of photosynthetic pigments and diatoms in the sediments of a microtidal fjord

• The depth distribution of photosynthetic pigments and benthic marine diatoms was investigated in late spring at three different sites on the Swedish west coast. At each site, sediment cores were taken at six depths (7-35 m) by scuba divers. It was hypothesized that (1) living benthic diatoms constitute a substantial part of the benthic micro. ora even at depths where the light levels are <1% of the surface irradiance, and (2) the changing light environment along the depth gradient will be reflected in ( a) the composition of diatom assemblages, and (b) different pigment ratios. Sediment microalgal communities were analysed using epifluorescence microscopy ( to study live cells), light microscopy and scanning electron microscopy ( diatom preparations), and HPLC ( photosynthetic pigments). Pigments were calculated as concentrations (mg m(-2)) and as ratios relative to chlorophyll a. Hypothesis (1) was accepted. At 20 m, the irradiance was 0.2% of surface irradiance and at 7 m, 1%. Living (epifluorescent) benthic diatoms were found down to 20 m at all sites. The cell counts corroborated the diatom pigment concentrations, decreasing with depth from 7 to 25 m, levelling out between 25 and 35 m. There were significant positive correlations between chlorophyll a and living (epifluorescent) benthic diatoms and between the diatom pigment fucoxanthin and chlorophyll a. Hypothesis (2) was only partly accepted because it could not be shown that light was the main environmental factor. A principal component analysis on diatom species showed that pelagic forms characterized the deeper locations (25-35 m), and epipelic-epipsammic taxa the shallower sites (7-20 m). Redundancy analyses showed a significant relationship between diatom taxa and environmental factors temperature, salinity, and light intensities explained 57% of diatom taxa variations.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

benthic

diatoms

photosynthetic pigments

sediment

hplc

water sandy sediment

microbenthic community

chlorophyll-a

microphytobenthos

nutrient

biomass

field

sea

denitrification

phytoplankton

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)