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Physical forcing and the dynamics of the pelagic ecosystem in the eastern tropical Pacific: simulations with ENSO-scale and global-warming climate drivers

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We used a model of the pelagic ecosystem in the eastern tropical Pacific Ocean to explore how climate variation at El Niño – Southern Oscillation (ENSO) scales might affect animals at middle and upper trophic levels. We developed two physical-forcing scenarios: (1) physical effects on phytoplankton biomass and (2) simultaneous physical effects on phytoplankton biomass and predator recruitment. We simulated the effects of climate-anomaly pulses, climate cycles, and global warming. Pulses caused oscillations to propagate through the ecosystem; cycles affected the shapes of these oscillations; and warming caused trends. We concluded that biomass trajectories of single populations at middle and upper trophic levels cannot be used to detect bottom-up effects, that direct physical effects on predator recruitment can be the dominant source of interannual variability in pelagic ecosystems, that such direct effects may dampen top-down control by fisheries, and that predictions about the effects of climate change may be misleading if fishing mortality is not considered. Predictions from ecosystem models are sensitive to the relative strengths of indirect and direct physical effects on middle and upper trophic levels.

Un modèle de l'écosystème pélagique du Pacifique oriental tropical nous a permis d'explorer comment des variations à l'échelle d'El Niño et de l'oscillation australe (ENSO) peuvent affecter les animaux des niveaux trophiques moyens et supérieurs. Nous avons imaginé deux scénarios de forçage physique : (1) les effets physiques sur la biomasse du phytoplancton et (2) les effets physiques simultanés sur la biomasse du phytoplancton et le recrutement des prédateurs. Nous avons simulé les effets des pulsations des anomalies climatique, de cycles climatiques et du réchauffement global. Les pulsations engendrent des oscillations qui se propagent dans l'écosystème, les cycles modifient la forme des oscillations et le réchauffement global engendre des tendances. Nos conclusions sont les suivantes : les trajectoires de la biomasse de populations isolées des niveaux trophiques moyens ou supérieurs ne peuvent servir à déceler les effets ascendants; les effets physiques qui affectent directement le recrutement des prédateurs peuvent être la source principale de la variation inter-annuelle dans les écosystèmes pélagiques; de tels effets directs peuvent tamponner le contrôle descendant exercé par la pêche commerciale; les prédictions sur les effets des changements climatiques peuvent être trompeurs, si on ne tient pas compte de la mortalité des poissons due à la pêche. Les prédictions des modèles d'écosystèmes sont aussi affectées par l'importance relative des effets physiques directs et indirects sur les niveaux trophiques moyens et supérieurs.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2003-09-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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