Fig. 4

Owing to the high concentration of nutrients, the Humboldt Current upwelling system is the most productive marine ecosystem of the world. Upwelling fuels high primary and secondary production by bringing nutrient-rich water to the surface layers. Under El Niño conditions water temperature increases and the thermocline drops, which limits upwelling to the nutrient-poor surface layer. This in turn reduces primary production. Thus, less energy can be assimilated by suspension feeding coastal marcobenthic species. Additionally, increased temperatures impact the organisms. Even when temperatures are not lethal, more energy is necessary for metabolism under stress. This means a greater amount of energy has to be allocated to metabolic energy and less “surplus” energy is available for reproduction and somatic growth. Temperature is often a trigger for the reproductive cycle, thus the temperature increase during EN may cause changes in an existing rhythm