EVIDENCE FOR A NOVEL PIGMENT WITH IN-VIVO ABSORPTION MAXIMUM AT 708 NM ASSOCIATED WITH PHAEOCYSTIS CF POUCHETII BLOOMS

The presence of a chlorophyll a-like (chi a) pigment, with an in vivo absorption maximum in the near-infrared region at 708 to 712 nm, was o bserved mainly in sedimenting material and Calanus hyperboreus fecal p ellets associated with Phaeocystis cf. pouchetii Harlot blooms. (In vi vo absorption is attributed to natural absorption found in naturally o ccurring particulate matter and seston. In vitro absorption refers to extracts in organic solvents.) This absorption peak was observed in co njunction with the absorption peak at 674 to 676 nm, commonly attribut ed to chi a and its derivatives. The in vivo absorption maximum in the near infrared, centered around 708 nm, was observed only in particula te matter and not in methanolic and aqueous acetonic extracts. Absorpt ion efficiency (Q(a)) of individual particles measured by microphotome try revealed particles 3 to 4 mu m in diameter with an in vivo absorpt ion maximum at 708 to 713 nm and no in vivo absorption peak at 676 nm, as expected for chlorophylls and its phaeopigments, indicating a diff erent type of particle in the sample. The visible spectrum also had a broad absorption peak in the blue region, between 420 and 450 nm, sugg esting a chlorophyll-like spectrum. The main chi degradation product a nalyzed by high-performance liquid chromatography of sedimenting matte r was identified as a phaeophorbide a-like pigment, with absorption ma ximum in the red at 665 to 666 mn in organic solvents, with no indicat ion of a pigment with in vitro absorption properties in the near infra red. The accumulation of the 708 nm in vivo absorption peak in particl es associated with P. cf. pouchetii seems to be a widespread feature a s it was observed during 3 different cruises to the Barents Sea, Fram Strait and the Kattegat. We propose 3 different hypotheses on the orig in of this novel. peak in in vivo absorption not previously observed i n marine environments: (1) P. cf. pouchetii has a chi a breakdown path way which promotes the accumulation of a known chi degradation product with an in vivo absorption at 708 mn; (2) there is a new chl degradat ion product produced by grazing of C. hyperboreus on P. cf. pouchetii, as yet to be isolated; and (3) there is a new pigment, synthesized by either P. cf. pouchetii or another organism associated with this alga , during mature blooms of Phaeocystis. These hypotheses are discussed in view of the available evidence.