No abstract

In the north-central zone of Chile (25°00’-31°40'S), zooplankton samples were taken in 103 oceanographic stations during February-March 2017 (0-70 m). Ostracods were separated, identified, and counted, making it possible to determine their distribution, abundance, species richness, and diversity. Twenty-one species belonging to 12 genera of the Halocyprididae family were identified, three of which had not been previously reported for the southeastern Pacific (Conchoecetta acuminata, Mikroconchoecia stigmatica, and Orthoconchoecia atlantica). The highest abundances, species richness, and diversity were found mainly in stations away from the coast (10 and 20 nm), sampled in hours of darkness. The most abundant species with the highest frequency of occurrence were Archiconchoecia striata, Conchoecetta giesbrechti, Conchoecia magna, and Halocypris inflata. A. striata constituted more than 50% of the total abundance of the ostracods identified.

The presence of juvenile Branchiostoma elongatum captured in plankton samples from the north-central coast of Chile during February-March of consecutive years (2013-2020) is described. Its low abundance showed interannual variation as well as its frequency of occurrence. Its geographical distribution was preferably coastal. It covered the entire sampling area (1-20 nm from the coast) longitudinally, and specimens were captured between the extreme north of the sampling area and 30°20’S. The lowest abundances were found in years of negative thermal anomalies (2017-2018) and the highest mainly in neutral conditions (2013-2015).