Decline in top predator body size and changing climate alter trophic structure in an oceanic ecosystem

Globally, overfishing large-bodied groundfish populations has resulted in substantial increases in their prey populations. Where it has been examined, the effects of overfishing have cascaded down the food chain. In an intensively fished area on the western Scotian Shelf, Northwest Atlantic, the bio...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 2010-05, Vol.277 (1686), p.1353-1360
Main Authors: Shackell, Nancy L., Frank, Kenneth T., Fisher, Jonathan A. D., Petrie, Brian, Leggett, William C.
Format: Article
Language:English
Subjects:
Animals
Biomass
Body Size
Climate
Climate Change
Ecosystem
Ecosystems
Functional groups
Gadiformes - classification
Gadiformes - growth & development
Marine ecosystems
Marine Fisheries
Marine fishes
Materials
Oceans and Seas
Phytoplankton - growth & development
Predators
Predatory Behavior - physiology
Species Specificity
Temperature
Trophic Interactions
Trophic levels
Trophic relationships
Zooplankton - growth & development
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Summary:Globally, overfishing large-bodied groundfish populations has resulted in substantial increases in their prey populations. Where it has been examined, the effects of overfishing have cascaded down the food chain. In an intensively fished area on the western Scotian Shelf, Northwest Atlantic, the biomass of prey species increased exponentially (doubling time of 11 years) even though the aggregate biomass of their predators remained stable over 38 years. Concomitant reductions in herbivorous zooplankton and increases in phytoplankton were also evident. This anomalous trophic pattern led us to examine how declines in predator body size (approx. 60% in body mass since the early 1970s) and climatic regime influenced lower trophic levels. The increase in prey biomass was associated primarily with declines in predator body size and secondarily to an increase in stratification. Sea surface temperature and predator biomass had no influence. A regression model explained 65 per cent of prey biomass variability. Trait-mediated effects, namely a reduction in predator size, resulted in a weakening of top predation pressure. Increased stratification may have enhanced growing conditions for prey fish. Size-selective harvesting under changing climatic conditions initiated a trophic restructuring of the food chain, the effects of which may have influenced three trophic levels.
ISSN:0962-8452
1471-2945
1471-2954
DOI:10.1098/rspb.2009.1020