Trophic and environmental drivers of the Sechura Bay Ecosystem (Peru) over an ENSO cycle

Abstract

Interannual environmental variability in Peru is dominated by the El Niño Southern Oscillation (ENSO). The most dramatic changes are associated with the warm El Niño (EN) phase (opposite the cold La Niña phase), which disrupts the normal coastal upwelling and affects the dynamics of many coastal marine and terrestrial resources. This study presents a trophic model for Sechura Bay, located at the northern extension of the Peruvian upwelling system, where ENSO-induced environmental variability is most extreme. Using an initial steady-state model for the year 1996, we explore the dynamics of the ecosystem through the year 2003 (including the strong EN of 1997/98 and the weaker EN of 2002/03). Based on support from literature, we force biomass of several non-trophicallymediated 'drivers' (e.g. Scallops, Benthic detritivores, Octopus, and Littoral fish) to observe whether the fit between historical and simulated changes (by the trophic model) is improved. The results indicate that the Sechura Bay Ecosystem is a relatively inefficient system from a community energetics point of view, likely due to the periodic perturbations of ENSO. A combination of high system productivity and low trophic level target species of invertebrates (i.e. scallops) and fish (i.e. anchoveta) results in high catches and an efficient fishery. The importance of environmental drivers is suggested, given the relatively small improvements in the fit of the simulation with the addition of trophic drivers on remaining functional groups' dynamics. An additional multivariate regression model is presented for the scallop Argopecten purpuratus, which demonstrates a significant correlation between both spawning stock size and riverine discharge-mediated mortality on catch levels. These results are discussed in the context of the appropriateness of trophodynamic modeling in relatively open systems, and how management strategies may be focused given the highly environmentally influenced marine resources of the region.

Latitudinal variation in the reproductive cycle of two bivalves with contrasting biogeographical origin along the Humboldt Current Upwelling Ecosystem

“…Several studies have suggested that the continuous gametogenic activity in A. purpuratus is a strategy of adaptation to the combination of environmental conditions, especially temperature and food availability (Illanes et al 1985, Wolff 1988, Avendaño et al 2008. A small seasonal increase in river inflow seems to disturb the gametogenic activity of A. purpuratus as seen in Paita (Taylor et al 2008). Low temperatures at the southern limit of the distributional range may limit the gametogenic activity to a shorter season.…”

Organismal biology joins climate research: the example of ENSO

“…Since the intensity and onset of EN and thus its impact on PaciWc South America strongly varies (Arntz and Fahrbach 1991), management advice tailored to small-scale users is necessary (i.e. Taylor et al 2008;Thatje et al 2008) to evaluate the variable responses of coastal ecosystems along PaciWc South America to climate oscillation, particularly as they have much less destructive track records of resource use than industrial-scale operations, at least unless they are forced into direct competition. …”

“…However, when trying to reveal the development and resilience potential of coastal marine communities, the lack or inaccessibility of information is a general concern Riascos et al 2008). Most studies on the biology and ecology of organisms occurring in upwelling regions are of descriptive nature and underlying processes that are driven by ENSO are far from being understood (Criales-Hernández et al 2008;Sotil et al 2008), which hampers the development of (short-term) predictive or response-management of key resources (Taylor et al 2008).…”

“…CENSOR targets the study of ENSO eVects on near-shore coastal environments and related socio-economics along PaciWc South America ). The present Special Issue of Helgoland Marine Research gives an overview of various scientiWc areas tackled within the project rather than aiming for an integrated view of the ecosystem and management problems associated with ENSO in PaciWc South America (Taylor et al 2008;Thatje et al 2008). The compilation of ongoing work clearly marks the complexity of the Humboldt Current ecosystem in response to both EN and LN, Special Issue: Climate variability and El Niño Southern Oscillation: implications for natural coastal resources and management.…”

El Niño induced changes to the Bolivar Channel ecosystem (Galapagos): comparing model simulations with historical biomass time series

“…The diet matrix of the reference model was modified in light of the fact that many groups are rather unselective, opportunistic feeders and that available food item proportions had changed due to the El Niño-caused changes in biomass of most groups. Following the method of Taylor et al (2008a), we thus adjusted the diet proportions to reflect predatory groups' consumption habits as well as the available production of prey groups. Moreover, an increased base percentage of detritus feeding (10%) was assumed for most benthic feeders, which is proximate to values given in Ortiz & Wolff (2002) and Taylor et al (2008b) for benthic compartments in a Chilean and Peruvian bay system, respectively.…”