Microbial dynamics during the decline of a spring diatom bloom in the Northeast Atlantic

• Published in: Journal of Plankton Research
• Main Authors: Llewellyn, Carole A., Tarran, Glen A., Galliene, Chris P., Cummings, Denise G., De Menezes, Alex, Rees, Andy P., Dixon, Jo L., Widdicombe, Claire E., Fileman, Elaine S., Wilson, Willie H.
• Format: Text
• Language: English
• Published: Oxford University Press 2007
• Subjects: Article; Northeast Atlantic
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/fbm104v1; https://doi.org/10.1093/plankt/fbm104

The microbial dynamics during a spring diatom bloom decline was monitored in the Northeast Atlantic during a five day Lagrangian study (8 - 12th April 2002). Phytoplankton abundance, composition and health status were related to viral and bacterial abundance, zooplankton abundance and grazing rates, and bacterial production. Phytoplankton reached maximum concentrations on Day 3 (Chl-a > 5 μg L−1) and declined on Day 5 (Chl-a ∼2 μg L−1) and was dominated (70% of Chl-a) by diatoms. Bacterial production increased substantially to>20 μg C L−1 d−1 on Day 3 and concomitantly large viruses decreased in number by half to < 10 x 103 mL−1. This was followed by a five fold increase in large viruses on Day 5 indicating infection and subsequent lysis on Days 3 and 5 respectively. Micro- and mesozooplankton grazing were not the principal cause for the decline of the bloom and pheophorbide-a showing little variation in concentration from Days 1 to 4 (approx 100 ng L−1) although doubled on Day 5. The poor physiological status of the diatoms, indicated by the high chlorophyllide-a concentrations (50 - 480 ng L−1), likely promoted a series of closely interrelated events involving bacteria and viruses leading to the demise of the diatom bloom.