Changes in N:P stoichiometry influence taxonomic composition and nutritional quality of phytoplankton in the Peruvian upwelling

Hauss, Helena, Franz, Jasmin and Sommer, Ulrich (2012) Changes in N:P stoichiometry influence taxonomic composition and nutritional quality of phytoplankton in the Peruvian upwelling Journal of Sea Research, 73 . pp. 74-85. DOI 10.1016/j.seares.2012.06.010.

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Abstract

Inorganic dissolved macronutrient (nitrogen, N, and phosphorus, P) supply to surface waters in the eastern tropical South Pacific is influenced by expanding oxygen minimum zones, since N loss occurs due to microbial processes under anoxic conditions while P is increasingly released from the shelf sediments. To investigate the impact of decreasing N:P supply ratios in the Peruvian Upwelling, we conducted nutrient manipulation experiments using a shipboard mesocosm setup with a natural phytoplankton community. In a first experiment, either N or P or no nutrients were added with mesozooplankton present or absent. In a second experiment, initial nutrient concentrations were adjusted to four N:P ratios ranging from 2.5 to 16 using two "high N" and two "high P" levels in combination (i.e., +N, +P, +N and P, no addition). Over six and seven days, respectively, microalgal biomass development as well as nutrient uptake was monitored. Phytoplankton biomass strongly responded to N addition, in both mesozooplankton-grazed and not grazed treatments. The developing diatom bloom in the "high N" exceeded that in the "low N" treatments by a factor of two. No modulation of the total biomass by P-addition was observed, however, species-specific responses were more variable. Notably, some organisms were able to benefit from low N:P fertilization ratios, especially Heterosigma sp. and Phaeocystis globosa which are notorious for forming blooms that are toxic or inadequate for mesozooplankton nutrition. After the decline of the diatom bloom, the relative contribution of unsaturated fatty acid to the lipid content of seston was positively correlated to diatom biomass in the peak bloom, indicating that positive effects of diatom blooms on food quality of the protist community to higher trophic levels remain even after the phytoplankton biomass was incorporated by grazers. Our results indicate an overall N-limitation of the system, especially in the case of dominating diatoms, which were able to immediately utilize the available nitrate (within two days) and develop a biomass maximum within three days of incubation. After the decline of diatom biomass, detection of the cyanobacterial marker pigment aphanizophyll indicated the occurrence of diazotrophs, especially in those enclosures initially provided with high N supply. This was surprising, as diazotrophs are thought to play a role in compensating to some extent the N deficit above OMZs in the succession of phytoplankton after an upwelling event

Document Type: Article
Additional Information: WOS:000309032600009
Keywords: Eastern boundary current; Fatty acids; Nutrient inventories; Oxygen minimum zone; Bacillariophyceae; Phaeocystis globosa; EASTERN TROPICAL PACIFIC; NUTRIENT-ENRICHMENT EXPERIMENTS; EGG HATCHING SUCCESS; NORTH-ATLANTIC OCEAN; PLANKTONIC FOOD-WEB; COMMUNITY COMPOSITION; NITROGEN-FIXATION; N-2 FIXATION; FATTY-ACIDS; PHOSPHORUS LIMITATION; Marine & Freshwater Biology; Oceanography
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > SFB 754 > B2
OceanRep > SFB 754
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
OceanRep > SFB 754 > B8
Refereed: Yes
DOI etc.: 10.1016/j.seares.2012.06.010
ISSN: 1385-1101
Related URLs:
Projects: SFB754
Date Deposited: 29 Oct 2012 14:33
Last Modified: 19 Jul 2017 10:37
URI: http://eprints.uni-kiel.de/id/eprint/16581

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