Biological parameters of the large jellyfish Chrysaora plocamia in central Peruvian coast, a ten-year study

Abstract

We report size structure, seasonal abundance, and overwinter of the Scyphozoa Chrysaora plocamia in Peru. Size structure was determined at the seasonal (2007-2009 and 2012-2018) and monthly (2016-2017) scales in the Pisco area (13°42’S – 14°08’S). Abundance was determined employed two methods: 1) By-catch biomass (kg jellyfish 1000 m-3) in the artisanal purse-seine fishery (2016-2017), and 2) seasonal occurrence area (km2) in the water column (2004-2007) in Bahia Independencia. Overwinter was determined by year-round presence/absence. We found a continuous size increase through time, from juvenile during winter, reaching the highest sizes during fall. The same pattern was also observed at monthly scales (Generalized Additive Model - GAM edf=8.96). C. plocamia abundances in both methods showed a steep increase from spring to summer, then decreased in fall and almost disappear in winter. Principal component analysis indicates that most of the variation was explained by C. plocamia size and sea surface temperature. Correspondence analysis revealed that large jellyfish sizes were associated to summer and fall. Two mass die-offs events were recorded in early winter 2012 and 2018. We conclude that C. plocamia follows the classic Metagenetic Life Cycle. Still, the presence of very few adults during winter would be a tiny fraction of the local population.