Phytoplankton pigments in relation to carbon content in phytoplankton communities

The in situ diet of the pearl oyster Pinctada margaritifera was determined in the lagoon of Takapoto Atoll by comparing the phytoplankton composition of water and bivalve gut contents using 2 different methods, optical microscopy and HPLC pigment analysis. In order to evaluate the available food resources for pearl oysters in the water column, a new method for estimating the pigment/chlorophyll a (chl a) ratio (based on an inverse analysis) was developed which allowed us to determine the contribution of the main phytoplanktonic groups in terms of chl a. In the water, picocyanobacteria and nanoflagellates predominated, the latter being mainly chlorophytes and prymnesiophytes. Comparisons between the results obtained by the 2 methods of investigation indicated that most of the dinoflagellates are unpigmented and, therefore, heterotrophic. An examination of the gut contents showed that picocyanobacteria were only weakly ingested by the oyster and, thus, nanoflagellates constituted the main food resource. Cryptophytes, although poorly represented in the water, were preferentially ingested. Chlorophytes were inefficiently hgested since they were found alive and motile in the faeces of the oyster. The ecological implications of this feeding behaviour are discussed.

Section: Discussionmentioning

confidence: 99%

Phytoplankton composition and selective feeding of the pearl oyster Pinctada margaritifera in the Takapoto lagoon (Tuamotu Archipelago, French Polynesia):in situ study using optical microscopy and HPLC pigment analysis

Loret¹,

Pastoureaud²,

Bacher³

et al. 2000

“…Filters were subsequently transferred to 3 ml acetone, sonicated on ice for 15 min, and left to extract for 24 h at 4°C prior to filtering (0.2 µm) into HPLC vials containing 1 ml water. HPLC analyses were performed on a Shimadzu LC 10A system with a Supercosil C18 column (250 × 4.6 mm, 5 µm) using a slight modification of the methodology of Wright et al (1991), as described in Schlüter & Havskum (1997). Pigments were identified by reten-tion times and absorption spectra identical to those of authentic standards, and quantified against standards purchased from the International Agency for 14 C Determination, Hørsholm, Denmark.…”

Section: Methodsmentioning

confidence: 99%

Pigment specific in vivo light absorption of phytoplankton from estuarine, coastal and oceanic waters

Stæhr

Markager²,

Sand‐Jensen³

2004

The influence of phytoplankton photoacclimation and adaptation to natural growth conditions on the chlorophyll a-specific in vivo absorption coefficient (a* ph ) was evaluated for samples collected in estuarine, coastal and oceanic waters. Despite an overall gradient in the physio-chemical environment from estuaries, over coastal, to oceanic waters, no clear relationships were found between a* ph and the prevailing light, temperature, salinity and nutrient concentrations, indicating that short-term cellular acclimation was of minor importance for the observed variability in a* ph . The clear decline in a* ph from oceanic, over coastal, to estuarine waters was, however, strongly correlated with an increase in cell size and intracellular chlorophyll a (chl a) content of the phytoplankton, and a reduction of photosynthetic carotenoids relative to chl a. Variations in photoprotective carotenoids relative to chl a seemed to be of minor importance for the variability in a* ph . In addition, significant differences in phytoplankton composition and abundance were observed, primarily driven by an increase in the abundance of diatoms, which furthermore correlated with increasing pigment packaging and decreasing a* ph . The observed differences in a* ph were, therefore, primarily driven by longerterm adaptations of the phytoplankton community. Our data suggests that an overall increase in nutrient loading from oceanic to estuarine waters increases phytoplankton abundance and favors larger sized species, particularly within the diatoms. These changes eventually decrease a* ph through a rise in the package effect and a lower abundance of photosynthetic carotenoids relative to chl a.

“…Chl a concentrations were determined fluorometrically for samples collected onto Whatman GF/F filters and extracted overnight at 4°C in 90% acetone. Phytoplankton pigment composition was analyzed by high pressure liquid chromatography (HPLC) according to the method of Wright et al (1991), with modifications described in Schlüter & Havskum (1997). The relative concentrations of marker pigments were obtained by relating the concentration of each marker pigment to the sum of the 8 marker pigments considered.…”

Section: Methodsmentioning

confidence: 99%

Spatial variability in bacterioplankton community composition at the Skagerrak-Kattegat Front

Pinhassi¹,

Winding²,

Binnerup³

et al. 2003

The distribution of bacterial heterotrophic production and cell concentrations in the world oceans is well documented. Nevertheless, information on the distribution of specific bacterial taxa and how this is influenced by environmental factors in separate sea areas is sparse. Here we report on bacterial community structure across the Skagerrak-Kattegat front. The front separates North Sea water from water with a Baltic Sea origin. We documented community differences across the front using denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified bacterial 16S ribosomal DNA and whole-genome DNA hybridization towards community DNA. Analysis of the community 'fingerprints' by DGGE revealed clustering of samples according to side of the front and depth. Consistent with these results, whole-genome DNA hybridization for 28 bacterial species isolated from the sampling region indicated that bacteria related to the Roseobacter clade and Bacteroidetes as well as prosthecate bacteria (e.g. Hyphomonas) showed distinct distribution patterns on each side of the front, and also with depth. Differences in bacterioplankton species composition across the frontal area were paralleled by differences in quantitative variables such as phytoplankton biomass (chl a), dissolved organic carbon, and bacterial production. Furthermore, we observed differences in more descriptive variables such as salinity range, bacterial growth-limiting nutrients and phytoplankton composition. We suggest that not only quantitative but also qualitative differences in variables that affect bacterial growth are required to cause divergence in bacterioplankton community composition between marine regions.