Abstract
Diatoms, a major component of the large-sized phytoplankton, are able to produce and release polyunsaturated aldehydes after cell disruption (potential PUAs or pPUA). These organisms are dominant in the large phytoplankton fraction (>10 µm) in the Strait of Gibraltar, the only connection between the Mediterranean Sea and the Atlantic Ocean. In this area, the hydrodynamics exerts a strong control on the composition and physiological state of the phytoplankton. This environment offers a great opportunity to analyze and compare the little known distribution of larger sized PUA producers in nature and, moreover, to study how environmental variables could affect the ranges and potential distribution of these compounds. Our results showed that, at both tidal regimes studied (Spring and Neap tides), diatoms in the Strait of Gibraltar are able to produce three aldehydes: Heptadienal, Octadienal and Decadienal, with a significant dominance of Decadienal production. The PUA released by mechanical cell disruption of large-sized collected cells (pPUA) ranged from 0.01 to 12.3 pmol from cells in 1 L, and from 0.1 to 9.8 fmol cell−1. Tidal regime affected the abundance, distribution and the level of physiological stress of diatoms in the Strait. During Spring tides, diatoms were more abundant, usually grouped nearer the coastal basin and showed less physiological stress than during Neap tides. Our results suggest a significant general increase in the pPUA productivity with increasing physiological stress for the cell also significantly associated to low nitrate availability.
Highlights
Diatoms often dominate the fraction of the large-sized phytoplankton in the ocean
Diatoms represented more than 70% of phytoplankton cell abundance at both tidal regimes (Table 1), followed by a 15%–20% of dinoflagellates and lower percentages of coccolitophorids and silicoflagellates (0.03% and 0.8%, respectively)
Diatom cell abundance varied from a minimum of 0.06 × 103 cell L−1 (St 28 under Neap tide regime) to a maximum of 50.9 × 103 cell L−1
Summary
Diatoms often dominate the fraction of the large-sized phytoplankton in the ocean. The reason of this ecological success still constitutes a matter of discussion and diverse mechanisms have been proposed to explain its widespread presence in the ocean [1,2,3]. There are oceanic areas where the microplanktonic fraction is usually dominated by diatoms and constitute valuable natural laboratories for the study of the ranges of variability of these compounds in natural conditions. This is the case of the Strait of Gibraltar, where diatoms represent a dominant phytoplankton group [16]. We examine the PUA productivity of the large-sized phytoplankton in the Strait of Gibraltar This area is the only connection between the Mediterranean Sea and the Atlantic. (as indicator of physiological stress in phytoplankton [22]) in order to find insight on the environmental control of PUAs production in nature
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