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Global change, zooplankton shifts, and C, N and P cycles in the southern ocean

AutorAlcaraz, Miquel ; Almeda, Rodrigo ; Duarte, Carlos M. ; Horstkotte, Burkhard ; Lasternas, Sebastien; Agustí, Susana
Fecha de publicación7-sep-2014
EditorRussian Academy of Sciences
CitaciónA variety of interactions in marine environment. Abstracts volume from 49th European Marine Biology Symposium: 65 (2014)
ResumenThe transfer of matter and energy from autotrophs to upper consumers in the Southern Ocean is essentially controlled by two groups of zooplankton, krill and salps. While krill (mainly Euphausia superba) is almost the unique food source for Antarctic fish, birds and mammals, salps (Salpa thompsoni) are of very indifferent nutritious value. Salps play a role at least as important as krill in the carbon cycle, filtering and packing biogenic carbon into larger and heavier faecal pellets than krill, thus accelerating the vertical flux of matter towards the long-lived and even sequestered carbon pools. Both groups show huge temporal and spatial fluctuations, with the irregular alternation of krill-dominated and salp-dominated years when salps, owing to their high rates of population growth and short life cycles dominate Antarctic zooplankton. At the same time, the continuous decreasing trend of krill populations along the last forty years has lead to predict a shift in Antarctic ecosystems, with the global substitution of krill by salps. The drivers of the change are not clear, but warmer temperatures, the extension of sea ice, and the decimation of whales appear as the most probable sources. Another consequence of the high warming rates in some Antarctic areas (i.e., the Antarctic Peninsula) would be the reduction of the individual biomass spectrum. Under these conditions, not only the populations depending of krill as food source will be severely threated, but the removal rates and fate of biogenic carbon, as well as the regeneration rates of nutrients by zooplankton excretion would change. With the objective of ascertaining the possible consequences for the cycling of biogenic carbon and the stoichiometry of regenerated nutrients of the predicted shifts in the Southern Ocean zooplankton we estimated the metabolic carbon requirements and inorganic N and P excretion rates of three major zooplankton groups in the Southern Ocean in the vicinity of the Antarctic Peninsula in February 2009. The carbon respiratory demands and NH4-N and PO4-P excretion rates of < 5 mm size copepods, krill (adult E. superba and E. crystalloropias and furcilia spp) and salps (blastozoids of Salpa thompsoni) were estimated by incubation experiments. The carbon-specific metabolic rates and N:P metabolic quotients of salps were higher than those of krill (furcilia spp. and adults) and copepods. There was also a negative relation between average individual zooplankton biomass and their metabolic rates, each metabolic process showing a particular response that leaded to different metabolic N:P ratios as a function of individual biomass. The predicted community shifts from krill to salps and the decrease of individual biomass in the Southern Ocean would therefore encompass not only the substitution of a pivotal group of Antarctic food webs (krill) by one of low nutritive value (salps). In a zooplankton community dominated by salps and of reduced individual size (biomass) there will be an increase of the zooplankton metabolic carbon demand and therefore of the proportion of primary production that should be allocated to compensate for the global zooplankton respiratory C-losses. At the same time, the production by salps of larger, faster sinking faecal pellets will increase the sequestration rate of biogenic carbon. Regarding the changes in excretion rates and N:P stoichiometry of the metabolic products by zooplankton, the characteristics of the dissolved nutrient pool could be modified, accelerating the changes on the functional and structural properties of primary producers (i.e., from diatoms to haptophytes) that would accelerate the change for the whole Antarctic ecosystem.
Descripción49th European Marine Biology Symposium (49TH EMBS), 7-12 september 2014, S. Petersburg, Russia.-- 1 page
Versión del editorhttp://www.onlinereg.ru/site.php?go=217&page=4917&lang=ENG
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(ICM) Comunicaciones congresos
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