Zooplankton biovolumes, abundance and distribution of ichthyoplankton, euphausiids, and cephalopod paralarvae (summer 2022)

Abstract

Zooplankton biovolumes ranged from 6.02x10^-4 and 7.23 mL.m^-3, averaging 0.53 mL.m^-3 with a median of 0.22 mL.m^-3 during the summer of 2022. The lower biovolumes (0.01-0.2 mL.m^-3) were more prevalent, accounting for 49.5 % of the samples, and were primarily concentrated along the coastal zone. Values exceeding 1 mL.m^-3 were scattered outside the continental shelf, notably off Punta Sal-Talara, Punta La Negra, Huarmey-Huacho, Callao, San Juan de Marcona, and Atico. Engraulis ringens was the most frequently observed ichthyoplankton species, comprising 51.96 % of the samples for eggs and 41.67 % for larvae. Ichthyoplankton densities varied from 4,000 to 10,000 eggs.m^-2, predominantly in the coastal area between Chimbote and Huarmey. Densities surpassing 1,000 larvae.m^-2 were observed between Malabrigo and Huarmey. Larvae were predominantly found in the size range of 3 to 3.5 mm (2,472 larvae.m^-2). The prevalent euphausiid species was Euphausia mucronata, with adults (34.8 %) and juveniles (29.9 %) distributed both within and beyond the continental shelf, spanning from Paita (north) to Ilo (south). Furcilia (45.59 %) and calyptopis stages (36.27 %) of “undetermined” species were common in the overall count, with a higher concentration within the shelf from north of Talara to the south of Punta La Negra and a more dispersed presence beyond the shelf in the central-southern zone, from Malabrigo to the south of Ilo. Concerning cephalopod paralarvae, Argonauta spp. were the most frequently encountered species (11.27 %), with a median count of 3 ind.m^-2.