A Comparison of DMSP Production in 3 Temperate Species of Phaeocystis (P. globosa, P. jahnii and P. cordata) at Saturating and Sub-saturating Irradiances.

This study investigated DMSP production in three temperate species of Phaeocystis; P .globosa, P. jahnii and P. cordata. P. globosa is a well-known bloom forming species that exists as both single cells and in a spherical colony form. On the other hand, P.jahnii and P. cordata are only known to exist in non-colonial, single celled forms. In addition to the well-documented blooms by the colony-forming species, the solitary cell Phaeocystis species have been suggested as potentially important components of open ocean picoplankton communities. Despite this, DMSP production P.jahnii and P.cordata has yet to be studied in cultures or compared to other Phaeocystis species. This study documents DMSP production in these species and compares it to both the single cell and colonial forms of P.globosa to better explain the role of single celled species of Phaeocystis in global DMSP dynamics. Four cultures of Phaeocystis (P.globosa CCMP 627, 629; P.jahnii CCMP 2496; P.cordata CCMP 3104) were grown at 20°C, with a 12:12hr light:dark cycle at 80μmol m-2 sec-1 in polystyrene flasks. The saturating irradiance for each species/strain was determined and a sub-saturating and saturating light treatment were created using GAM mylar neutral density filters. Particulate DMSP, particulate DMSO, POC, chl a, cell number and cell volume were measured daily in each culture. Overall, DMSP:chl a ratios increased with increasing irradiance for all species. DMSP:chl a ratios in P.jahnii and P.cordata were significantly higher than in single celled and colonial P.globosa. But, DMSP:cell volume remained constant across all species indicating that light level affected Chl a but not DMSP. Both P.jahnii and P.cordata produced significant amounts of DMSP and these data illustrate that the species that exist only as solitary cells could play important roles in global DMSP dynamics as part of the picoplankton community, and their contribution to global DMSP production warrants further investigation.