New insights into the abundance and seasonal distribution of the Portuguese man-of-war Physalia physalis (Cnidaria: Siphonophorae) in the southeastern Pacific

Abstract

During summer 2017 an anomalous and unprecedented developing of warm water off the coast of Chile was presented, namely Coastal El Niño event. Coincidentally, a high amount of strandings of Portuguese Man-of-War (Physalia physalis) were present at that time. In this work we determine the latitudinal and seasonal distribution of the pleustonic siphonophore P. physalis in the southeastern Pacific, from January 2016 to December 2017. The northernmost and southernmost records for the southeastern Pacific were recorded in this study, from Arica (18∘26’S; 70∘18’W) to Quellón (43∘21’S; 74∘07’W) in Chile, respectively. During the surveyed period, the greatest strandings of this species were recorded both in the north (23∘S) and south of Chile (36–38∘S) during the austral summer months, coinciding when sea surface is relatively warmer. The number of strandings registered in 2017 was more than 4 times the number of strandings during 2016; this is 17339 colonies in 2017 and 3910 colonies in 2016. The association between the maximum observed strandings and the time of appearance of Coastal El Niño event during summer 2017 are also discussed. Our findings can be used as guidance in the monitoring of P. physalis, in order to prevent encounters and therefore possible accidents with humans in coastal waters and beaches by strandings.