MEPS 441:15-24 (2011)  -  DOI: https://doi.org/10.3354/meps09353

ABSTRACT: Direct interactions between phytoplankton and bacteria are hypothesized to impact bloom dynamics, community succession, and primary productivity. Such impacts may be dependent upon bacterial attachment to phytoplankton, but few studies have quantified this relationship in natural marine waters and little is known regarding factors regulating attachment. During a study of thin layer dynamics in Monterey Bay, California, USA, we collected over 18000 phytoplankton cells and analyzed them for attached bacteria. We focused our statistical analysis on abundant diatoms and dinoflagellates often associated with thin layers and surface slicks. More than 90% of phytoplankton cells analyzed did not harbor attached bacteria. When colonization had occurred, a single attached bacterium was the most common occurrence and few cells had multiple attached bacteria. Visually healthy phytoplankton were rarely colonized, but those collected outside of dense thin layers and surface slicks had higher incidences of colonization and were more likely to harbor multiple bacteria. Longer diatom chains had a higher probability of being colonized and of bacteria being selectively attached to specific regions within the chains. These results strongly suggest that phytoplankton abundance, health, and morphology regulate colonization by bacteria in the natural marine environment.

KEY WORDS: Bacteria · Colonization · Attachment · Diatom · Dinoflagellate · Monterey Bay · Thin layers