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

Abstract

During a strong El Niño event, nutrient and phytoplankton concentrations around the Galapagos archipelago greatly decrease, while sea surface temperature increases (> 7°C). Several species suffer under these conditions, while some benefit and new species appear. To understand the mechanisms behind observed changes, a trophic reference model of the Bolivar Channel ecosystem was forced by a 16 yr (1994 to 2009) satellite-derived time series of phytoplankton biomass including the El Niño period 1997/98. Emergent changes in model compartment biomasses, as derived from dynamic simulations, were compared to in situ observations of the subtidal communities and marine vertebrates over the study period. Observed population reductions of seabirds (penguins and flightless cormorants) and of several fish groups were well predicted by the simulations, suggesting that bottom-up effects largely control the system during an El Niño event. Observational data also enabled modifying the reference model to an El Niño state model. In this El Niño model, ecosystem size (total energy throughput) was reduced by 70.1%. Overall system characteristics show great similarities with other coastal upwelling systems of the Peruvian coast in that strong El Niño events cause disruptions to trophic flows and keep them at a low (but highly productive) development state.

Impacts of Climate Variability on Latin American Small-scale Fisheries

“…Thus, heavily grazed reefs with crustose coralline algae, "urchin barrens," replaced former macroalgal and coral habitats, resulting in declines in biodiversity (Edgar et al 2010). Wolff et al (2012a) evaluated the dynamics of subtidal communities and marine vertebrates during the period 1994-2009, based on a trophic mass balance model of the Bolivar Channel ecosystem, the most productive area of the archipelago. These authors showed that SST increased by 7°C during the 1997/1998 El Niño, when phytoplankton concentration decreased by 46% and 33%, respectively, and the ecosystem size (total energy throughput) was reduced by 70%.…”

“…This was reflected in the reduction of pelagic and demersal fish, seabirds, reptiles, and marine mammals. Wolff et al (2012a) suggested that bottomup effects largely control the system during El Niño events.…”

“…The high production levels registered for the sea cucumber SSF in 2002 have been the combined result of two main factors (Hearn et al 2005, Castrejón 2011, Wolff et al 2012a): (1) a strong recruitment pulse triggered by the 1997/1998 El Niño that led to unusually high stock densities during years 2000-2003; and (2) an increase in fishing effort that resulted from the opening of the sea cucumber artisanal fishery in 1999. Sea cucumber recruits increased in density by a factor of 20 in the west part of the archipelago (Hearn et al 2005).…”

“…After 1998, warm anomalies associated with ENSO have been mostly confined to the central Pacific Ocean (Lee and McPhaden 2010). Thus, Galápagos experienced an extended cool regime during the last decade, which together with overfishing might be responsible for the low levels of sea cucumber recruitment (Wolff et al 2012a). The combined effects of poor recruitment and high fishing levels have severely affected this SSF, leading to its closure in 2006, 2009, 2010, and 2012.…”

Weather, Hydrological and Oceanographic Conditions of the Northern Coast of the Río de la Plata Estuary during ENSO 2009–2010

“…Surface ocean temperature is the most analyzed oceanographic variable regarding the "El Niño" phase and its ecosystem effects in oceanic and coastal marine zones [13]. Nevertheless, estuarine zones are expected to experience a greater impact of hydrologic effects (fresh water or ocean water inputs) [14].…”