Dancing with the Tides: Fluctuations of Coastal Phytoplankton Orchestrated by Different Oscillatory Modes of the Tidal Cycle

• Published in: PloS one Vol. 7; no. 11; p. e49319
• Main Authors: Blauw, Anouk N., Benincà, Elisa, Laane, Remi W. P. M., Greenwood, Naomi, Huisman, Jef
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 14.11.2012; Public Library of Science (PLoS)
• Subjects: Algae; Analysis; Animal behavior; Automation; Biodiversity; Biology; Chlorophyll; Chlorophyll - metabolism; Coastal environments; Coastal waters; Diurnal variations; Earth Sciences; Ecology; Ecosystems; Environmental monitoring; Estuaries; Eutrophication - physiology; Fluctuations; Fluorescence; Hypotheses; Light; Natural variability; Neap tides; North Sea; Particulate matter; Particulate Matter - analysis; Periodicities; Phytoplankton; Phytoplankton - growth & development; Plankton; Population Dynamics; Population growth; Salinity; Sediments; Tidal currents; Tidal cycles; Tidal mixing; Tidal Waves; Time Factors; Time series; Vertical mixing; Wavelet analysis; North Sea; Netherlands
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0049319

Population fluctuations are often driven by an interplay between intrinsic population processes and extrinsic environmental forcing. To investigate this interplay, we analyzed fluctuations in coastal phytoplankton concentration in relation to the tidal cycle. Time series of chlorophyll fluorescence, suspended particulate matter (SPM), salinity and temperature were obtained from an automated measuring platform in the southern North Sea, covering 9 years of data at a resolution of 12 to 30 minutes. Wavelet analysis showed that chlorophyll fluctuations were dominated by periodicities of 6 hours 12 min, 12 hours 25 min, 24 hours and 15 days, which correspond to the typical periodicities of tidal current speeds, the semidiurnal tidal cycle, the day-night cycle, and the spring-neap tidal cycle, respectively. During most of the year, chlorophyll and SPM fluctuated in phase with tidal current speed, indicative of alternating periods of sinking and vertical mixing of algal cells and SPM driven by the tidal cycle. Spring blooms slowly built up over several spring-neap tidal cycles, and subsequently expanded in late spring when a strong decline of the SPM concentration during neap tide enabled a temporary "escape" of the chlorophyll concentration from the tidal mixing regime. Our results demonstrate that the tidal cycle is a major determinant of phytoplankton fluctuations at several different time scales. These findings imply that high-resolution monitoring programs are essential to capture the natural variability of phytoplankton in coastal waters.