Dynamics of phytoplankton groups in three contrasting situations of the open NW Mediterranean Sea revealed by pigment, microscopy, and flow cytometry analyses

Mikel Latasa, Renate Scharek, Xose Anxelu G. Moran, Andrés Gutiérrez-Rodríguez, Mikhail Emelianov, Jordi Salat, Montserrat Vidal, Marta Estrada

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

A detailed study of phytoplankton composition and dynamics was carried out during three contrasting situations (cruises F1, F2, and F3) in the northwestern (NW) Mediterranean Sea. Haptophytes, diatoms, and green algae dominated in F1, during the spring bloom, with high nutrients and high phytoplankton biomass. In F2, the post-bloom situation with a still weak stratification and lower nutrient concentrations, we found a high spatial variability. Stations were clearly dominated by either Synechococcus, haptophytes or cryptophytes; with Synechococcus reaching the highest abundance (4 × 105 cells mL−1, 60% of the integrated chlorophyll a) reported to date for the open Mediterranean Sea. Cryptophytes accumulated close to the surface in very shallow mixed layer stations. In late summer, F3 revealed a fully developed stratification with low nutrients and a marked deep chlorophyll maximum (DCM). Prochlorococcus was present only during this cruise, mainly in deep layers together with haptophytes and pelagophytes, while haptophytes and Synechococcus dominated the upper mixed layer. Flow cytometry (FCM) and pigment-based abundance estimates for Prochlorococcus, Synechococcus and cryptophytes were well correlated, as happened also between small picoeukaryotes (FCM) and green algae (pigments), and between large picoeukaryotes (FCM) and haptophytes (pigments). Dinoflagellate abundance by microscopy and by pigments did not agree well, probably due to the presence of heterotrophic forms or because they contained pigments other than peridinin, the standard dinoflagellate marker. The decrease in size of the FCM large picoeukaryotes group with depth was presumably related to the increasing contribution of pelagophytes, with smaller cells than haptophytes, the other main component of this fraction. Cell size increase of Prochlorococcus and Synechococcus with depth suggests vertical segregation of genotypes or photoadaptation. The groups' ecological preferences are presented with respect to depth and nutrient concentrations. Synechococcus and cryptophytes occupied shallow layers; diatoms, green algae and Prochlorococcus showed a tendency for deep layers and pelagophytes for even deeper layers, while haptophyte and dinoflagellate allocations were less clear. As for nutrients, the maximum relative contributions of green algae and especially diatoms occurred when dissolved inorganic phosphorus (DIP) concentrations were highest, of Prochlorococcus, dinoflagellates and pelagophytes when lowest, and of Synechococcus and cryptophytes when DIP concentrations were low but not minimal. The contribution of haptophytes did not show a relationship with DIP concentration. These results from individual groups stand as significant exceptions to the general relationship between phytoplankton cell size and nutrient availability.
Original languageEnglish (US)
Pages (from-to)102737
JournalProgress in Oceanography
Volume201
DOIs
StatePublished - Dec 24 2021

Bibliographical note

KAUST Repository Item: Exported on 2022-10-14
Acknowledgements: We thank the captain and crew of R/V Sarmiento de Gamboa and the Marine Technology Unit (UTM) for their co-operation and support during the cruises. We thank Carmen Cabeza and Felipe González for their help with HPLC pigment and microscopy analyses, and Alejandro Isla for his help with figure preparation and data processing. The thoughtful comments of two anonymous reviewers helped to improve the manuscript. This work was funded by Spanish Government, Ministerio de Ciencia e Innovación (project FAMOSO, grant CTM2008-06261-C03/MAR). AGR was also supported by the Generalitat de Catalunya (Grup de Recerca 2061).

ASJC Scopus subject areas

  • Aquatic Science
  • Geology

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