Evidence for a novel pigment with in vivo absorption maximum at 708 nm associated with Phaeocystis cf. pouchetii blooms

Abstract

The presence of a chlorophyll a-like (chl a) pigment, with an in vivo absorption maximum in the near-infrared region at 708 to 712 nm, was observed mainly in sedimenting material and Calanus hyperboreus fecal pellets associated with Phaeocystis cf. pouchetii Hariot blooms. (In vivo absorption is attributed to natural absorption found in naturally occurring particulate matter and seston. In vitro absorption refers to extracts in organic solvents.) This absorption peak was observed in conjunction with the absorption peak at 674 to 676 nm, commonly attributed to chl a and its derivatives. The in vivo absorption maximum in the near infrared, centered around 708 nm, was observed only in particulate matter and not in methanolic and aqueous acetonic extracts. Absorption efficiency (Q(a)) of individual particles measured by microphotometry revealed particles 3 to 4 μm in diameter with an in vivo absorption maximum at 708 to 713 nm and no in vivo absorption peak at 676 nm, as expected for chlorophylls and its phaeopigments, indicating a different type of particle in the sample. The visible spectrum also had a broad absorption peak in the blue region, between 420 and 450 nm, suggesting a chlorophyll-like spectrum. The main chl degradation product analyzed by high-performance liquid chromatography of sedimenting matter was identified as a phaeophorbide a-like pigment, with absorption maximum in the red at 665 to 666 nm in organic solvents, with no indication of a pigment with in vitro absorption properties in the near infrared. The accumulation of the 708 nm in vivo absorption peak in particles associated with P. cf. pouchetii seems to be a widespread feature as it was observed during 3 different cruises to the Barents Sea, Fram Strait and the Kattegat. We propose 3 different hypotheses on the origin of this novel peak in in vivo absorption not previously observed in marine environments: (1) P. cf. pouchetii has a chl a breakdown pathway which promotes the accumulation of a known chl degradation product with an in vivo absorption at 708 nm; (2) there is a new chl degradation 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.