[OANNES Foro] Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

[raul sanchez]

Progress In Oceanography
Volume 79, Issues 2-4, October-December 2008, Pages 366-378 
The Northern Humboldt Current System: Ocean Dynamics, Ecosystem Processes, and Fisheries 
doi:10.1016/j.pocean.2008.10.008    

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO 

Marc H. Taylora, , , Jorge Tamb, Verónica Blaskovicb, Pepe Espinozab, R. Michael Ballónb, c, Claudia Wosnitza-Mendob, Juan Argüellesb, Erich Díazb, Sara Purcab, Noemi Ochoad, Patricia Ayónb, Elisa Goyab, Dimitri Gutiérrezb, Luis Quipuzcoab and Matthias Wolffa

aCenter for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany

bInstituto del Mar del Perú, Esq. Gamarra y Valle s/n, Apartado 22, Callao, Peru

cIRD, UR097, CRH, Avenue Jean Monnet, 34203 Sete, France

dUniversidad Nacional Mayor de San Marcos, Apartado 12, Lima, Peru

Abstract
The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú
 (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.

Keywords: Coastal upwelling; Ecosystem disturbance; El Niño phenomena; Trophic relationships; Trophodynamic model; Peru Humboldt Current


Saludos,

Raúl E. Sánchez Scaglioni