Rhythmicity of picoeukaryotes
Rhythmicity of coastal marine picoeukaryotes, bacteria and archaea despite irregular environmental perturbations
Abstract
Seasonality in marine microorganisms has been classically observed in phytoplankton blooms, and more recently studied at the community level in prokaryotes, but rarely investigated at the scale of individual microbial taxa across the three domains of life. Here we test if specific marine eukaryotic, bacterial and archaeal taxa display yearly rhythms at a coastal site impacted by irregular environmental perturbations. Our seven-year study in the Bay of Banyuls (North Western Mediterranean Sea) shows that despite some fluctuating environmental conditions, many microbial taxa displayed significant yearly rhythms. The robust rhythmicity was found in both autotrophs (picoeukaryotes and cyanobacteria) and heterotrophic prokaryotes. Sporadic meteorological events and irregular nutrient supplies did, however, trigger the appearance of less common non-rhythmic taxa. Among the environmental parameters that were measured, the main drivers of rhythmicity were temperature and day length. Seasonal autotrophs may thus be setting the pace for rhythmic heterotrophs as there are no real evidence of a genuine circadian clock in the latter. Similar environmental niches may be driving seasonality as well. The observed strong association between Micromonas and SAR11 OTUs, which both need thiamine precursors for growth, could be a first indication that shared nutritional niches may indeed explain some rhythmic patterns of co-occurrence.