On the trophic fate of Phaeocystis pouchetii. VII. Sterols and fatty acids reveal sedimentation of P. pouchetii-derived organic matter via krill

Abstract

As part of a joint project on the fate of phytoplankton in Balsfjorden in Northern Norway, we investigated the trophic fate and sedimentation potential of Phaeocystis pouchetii by tracing the transition of biomarker patterns from a phytoplankton bloom to sediment traps and during a gutpassage experiment. The phytoplankton biomass during the spring bloom 1996 was dominated by colonial P. pouchetii (ca 85%) and 4 members of the diatom family Thalassiosiraceae (ca 10%). Particulate organic carbon in sediment traps largely consisted of fecal material from the Arctic krill Thysanoessa sp. Sterol and fatty acid biomarker patterns in the phytoplankton bloom could be reproduced by combining the individual biomarker patterns of the isolated phytoplankters P. pouchetii and Thalassiosira decipiens in a ratio of ca 75:25. In a laboratory experiment, Arctic krill (Thysanoessa raschii) fed with similar efficiency on P. pouchetii colonies and the Thalassiosiraceae. During gut passage, the abundance of Thalassiosiraceae biomarkers in fecal strings increased relative to P. pouchetii biomarkers, while biomarkers from krill became dominant. This transition of biomarker patterns due to gut passage in T. raschii closely resembled the biomarker transition from the surface bloom to material in sediment traps at 40 to 170 m depth, which was mainly composed of krill fecal strings. We conclude that krill grazed efficiently on P. pouchetii colonies in Balsfjorden and caused sedimentation of P. pouchetii-derived organic matter below the euphotic zone via fecal strings. Hence, both transfer to higher trophic levels and sedimentation of Phaeocystis spp.-derived organic matter can be more effective than is commonly believed. KEY WORDS: Phaeocystis · Diatoms · Krill · Trophic fate · Vertical flux · BiomarkersResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 209: 55-69, 2001 rates of recognizable Phaeocystis spp. colonies and cells are low (Wassmann 1994 and references therein, Andreassen &Wassmann 1998). In contrast, the sudden disappearance of Phaeocystis spp. blooms from the euphotic zone, the existence of nitrate-depleted, silicate-rich water bodies with low phytoplankton concentrations in the vicinity of Phaeocystis spp. blooms (Wassmann et al. 1990, Smith et al. 1991, and the occurrence of pigments and dimethylsulphoniopropionate (DMSP) typical of Phaeocystis spp. in deeper layers and the sediment (di Tullio et al. 1996(di Tullio et al. , 2000 have suggested efficient sedimentation of Phaeocystis spp.-derived organic matter to aphotic zones in spite of the low sedimentation potential of Phaeocystis spp. aggregates (Riebesell 1993, Passow & Wassmann 1994, Riebesell et al. 1995.Arctic krill were argued to be largely responsible for the vertical flux of particulate organic carbon in Balsfjorden, where krill feces dominated sedimentation during Phaeocystis pouchetii blooms (Lutter et al. 1990, Riebesell et al. 1995. The resulting proposition that krill grazed efficiently on P. pouch...

Lipid biomarkers and trophic linkages between ctenophores and copepods in Svalbard waters

“…The dinoflagellates tend to be rich in 18:4n3, 18:5n3 and especially 22:6n3, but deficient in 16:1n7. Phaeocystis pouchetii, a species that often dominates the blooms in polar waters, tend to be characterised by this pattern (Sargent et al 1985, Hamm et al 2001. The synthesised data in Table 4 indicate that diatoms were the dominating food source of Calanus spp.…”

Anomalously low zooplankton abundance in the Ross Sea: An alternative explanation

“…In addition, P. antarctica colonies have a tough outer skin and can reach up to 2 mm in diameter (Hamm 2000), allowing them to resist grazing by microzooplankton once the colonial stage is reached (Bautista et al 1992). As a result, microzooplankton have a minimal grazing impact upon phytoplankton stocks in the Ross Sea (Caron et al 2000).…”

“…While the colonial habit of many Phaeocystis species prevents grazing by the smaller microzooplankton, Hansen et al (1994) suggest that mesozooplankton and macrozooplankton, such as L. helicina and the raptorial feeder M. gerlachei, are able to actively graze large colonies of P. antarctica. Hamm et al (2001) found that Phaeocystis colonies were a potentially valuable food source due to their high fatty acid composition. Lebour (1922) observed feeding on Phaeocystis sp.…”

Chemical cues induce consumer-specific defenses in a bloom-forming marine phytoplankton

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