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Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

Surma S, Pakhomov EA, Pitcher TJ - PLoS ONE (2014)

Bottom Line: An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend.Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown.The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

View Article: PubMed Central - PubMed

Affiliation: Fisheries Centre, University of British Columbia, Vancouver, BC, Canada.

ABSTRACT
The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

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The changes in predator biomass densities coincident with the peak “krill surplus” in the first three Ecosim scenarios.
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pone-0114978-g009: The changes in predator biomass densities coincident with the peak “krill surplus” in the first three Ecosim scenarios.

Mentions: For each Ecosim scenario, the changes in krill biomass density over the model run time are shown in Fig. 8. The effects of the peak “krill surplus” on predator biomasses in the scenarios where such a surplus appeared are shown in Fig. 9.


Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

Surma S, Pakhomov EA, Pitcher TJ - PLoS ONE (2014)

The changes in predator biomass densities coincident with the peak “krill surplus” in the first three Ecosim scenarios.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269391&req=5

pone-0114978-g009: The changes in predator biomass densities coincident with the peak “krill surplus” in the first three Ecosim scenarios.
Mentions: For each Ecosim scenario, the changes in krill biomass density over the model run time are shown in Fig. 8. The effects of the peak “krill surplus” on predator biomasses in the scenarios where such a surplus appeared are shown in Fig. 9.

Bottom Line: An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend.Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown.The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

View Article: PubMed Central - PubMed

Affiliation: Fisheries Centre, University of British Columbia, Vancouver, BC, Canada.

ABSTRACT
The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

Show MeSH
Related in: MedlinePlus