The larval and benthic stages of the scyphozoan medusa Chrysaora plocamia under El Niño–La Niña thermal regimes

• El Niño/La Niña anomalies affect performance of early life stages of C. plocamia.
• Larval and benthic stages of scyphozoans perform better within thermal optima.
• Thermal optima are species-specific, resembling site-specific environmental seasonality.
• Warming scenarios would not favour abundance of scyphozoan larval and benthic stages.

Jellyfish particularly scyphozoan population blooms appear to be increasing in strength and frequency in recent decades but efforts to understand drivers of population variability are hampered by the limited understanding of the ecology of the larval and benthic stages of the majority of species which may ultimately determine the abundance of the pelagic phase. Planula larvae and polyps of the large scyphomedusa Chrysaora plocamia inhabiting the Humboldt Current Upwelling System of Chile and Peru were experimentally exposed to temperature regimes representing El Niño–La Niña and Neutral conditions. Settlement of planulae was significantly affected only by El Niño temperature whereas survivorship of polyps was affected by both El Niño and La Niña temperatures. Somatic growth of polyps was negatively affected by both La Niña and El Niño temperatures although responses changed over the course of the experiment: whereas La Niña caused a longer term effect on the growth of polyps, under El Niño this showed a rapid recovery after an initial decrease in somatic growth. Therefore we concluded that increased abundances of the pelagic phase of C. plocamia observed during El Niño cannot be attributed to improved conditions for settlement of larvae growth or survivorship of the benthic stage. A comparative analysis of the effects of temperature on settlement and metamorphosis of larvae and survivorship of polyps of scyphozoans showed that the performance of animals in these stages is higher within a species-specific thermal range which reflects seasonal temperature variability of their environment.