Differential contribution of diatoms and dinoflagellates to phytoplankton biomass in the NE Atlantic Ocean and the North Sea

Abstract

Sampling by the continuous plankton recorder (CPR) survey over the North Atlantic Ocean and the North Sea has enabled long-term studies of phytoplankton biomass. Analysis of an index of phytoplankton biomass, the phytoplankton colour index (PCI), has previously shown an increase in phytoplankton biomass in the NE Atlantic. In the current study, further investigations were conducted to determine the contribution of diatom and dinoflagellate cell counts to the PCI, their fluctuations over the last 45 yr and their geographical variations in the eastern North Atlantic and the North Sea. An increased contribution of dinoflagellates to the PCI was revealed over the south NE Atlantic and the northern North Sea. In contrast, the contribution of diatoms decreased in the north NE Atlantic and the northern North Sea. No discernible trends were found in the other regions of the North Sea. The relative contributions of diatoms and dinoflagellates to the PCI led to the identification of 3 geographically distinct dynamic regimes in the diatom/dinoflagellate dynamics in the NE Atlantic and the North Sea. Finally, it is stressed that the discrepancy observed in the patterns of PCI and diatom and dinoflagellate cell counts suggests that changes in PCI do not reflect changes in the community structure and that the exclusive use of PCI is not adequate to investigate the long-term trends in the trophic link between phytoplankton and herbivorous zooplankton.

Distribution of micro-organisms along a transect in the South-East Pacific Ocean (BIOSOPE cruise) using epifluorescence microscopy

“…9) decreased towards the hyper-oligotrophic zone and increased towards the mesotrophic and eutrophic zones. This is in agreement with Leterme et al (2006) who showed that the dinoflagellate abundances increased with trophic status in the NE Atlantic Ocean. The observed increase in heterotrophic dinoflagellates contribution with depth is coherent with previous observations in the Equatorial Pacific (Chavez et al, 1990).…”

High-resolution analysis of a North Sea phytoplankton community structure based on in situ flow cytometry observations and potential implication for remote sensing

“…Such low abundances were found for some of the clusters identified in this study (NanoORG, MicroORG and Micro2 clusters for which the median abundance value was close to 30 cells cm −3 ), in agreement with concentrations observed in previous studies for the possibly related phytoplankton genus, as discussed below, i.e. cryptophytes (Buma et al, 1992), diatoms and dinoflagellates (Leterme et al, 2006). Previous comparisons between bench-top flow cytometry and remote sensing (Zubkov and Quartly, 2003) could technically not include the entire size range of nano-to microphytoplankton.…”

Estimation of the Potential Detection of Diatom Assemblages Based on Ocean Color Radiance Anomalies in the North Sea

“…In particular, the CPR dataset (5,977 samples, Figure 1) recorded an abundance of 72 diatom species or taxa over the period 1998-2010, representing from 40 to 90% of the total microphytoplankton abundance in Summer (June-August) and Spring (March-June), respectively (Leterme et al, 2006). These diatoms are identified at a species or taxonomic level (one taxon could represent more than one species).…”

“…For this purpose, the CPR diatom database from the North Sea and the English Channel were used (Figure 1). Broadly, diatoms represent a dominant taxon in the North Sea, at least during part of the year, with an abundance contribution from 40 to 90% of total microphytoplankton (Reid et al, 1990;Leterme et al, 2006). Please note that here the term "dominant" has not the same meaning that the one used in PHYSAT (see definition n • 6 in Supplementary Material).…”