Is chain length in phytoplankton regulated to evade predation?

Oda Bjærke, Per R. Jonsson, Asraful Alam, Erik Selander
2015 Journal of Plankton Research  
Many dominating phytoplankton form chains of attached cells. Chain length strongly influences how the organism interacts with its environment, but the factors driving the evolution of chain formation and chain length plasticity are not entirely clear. We tested the hypothesis that chain formation in diatoms is a grazer avoidance strategy. We modelled the effect of chain length plasticity on grazing mortality in Skeletonema marinoi over a temperate year, based on empirical data on grazer
more » ... s, induced chain length plasticity, and grazing rates. The predicted optimal chain length strategy was compared with field data of S. marinoi and copepod biomass. We found that low copepod densities, corresponding to spring conditions in the field, induced chain length reduction in S. marinoi. Modelled grazing risk over an annual cycle showed that fixed traits with either single cells or long chains have respectively 31 % and 36 % higher mortality than S. marinoi with grazer induced chain length plasticity. Field measurements of chain length and grazer abundances also agree well with chain length plasticity as a grazer defense strategy. We conclude that grazer regime could be a major driving force in the evolution of chain length plasticity in phytoplankton organisms.
doi:10.1093/plankt/fbv076 fatcat:zldgcgqgebfexfba7uqco6syru