First Assessment of Copepods Feeding in a Marine Reserve of the Humboldt's Archipelago

Abstract

The function and structure of coastal marine ecosystems are tightly coupled to zooplankton dynamics and processes, yet no attempt to address these issues has been made in the Humboldt’s Archipelago. Belonging to the Coquimbo upwelling system in central-northern Chile, the archipelago holds several marine reserves which congregate a high marine diversity involving several trophic levels and endemic species. Over the course of the El Niño 2023-year, copepod community clearance (CR) and ingestion rates (IR) of Calanus chilensis, Calanoides patagoniensis, Metridia lucens and Paracalanus sp., were studied in a marine reserve of the archipelago, the Chañaral de Aceituno Island, in relation to phytoplankton biomass (Chl) and particulate organic carbon (POC) concentration. Four grazing experiments were carried out with single copepod species across different year seasons and upon variable food availability. Phytoplankton biomass was relatively low (<2 µg Chl L-1) and exhibited temporal changes likely related to the seasonal transition over the year. The POC concentration was relatively high (180 µg C L-1) and constant throughout the experiments. Copepod feeding responses were associated with food availability, and there were significant differences in CR and IR among copepod species. Daily ration varied from 4% in large-sized and likely herbivorous C. chilensis and C. patagoniensis species, to 160% in the small-sized and omnivorous Paracalanus sp. Current findings are discussed considering different foraging strategies and upwelling-driven changes in food availability, seeking to contribute to the understanding of zooplankton-mediated processes supporting the productivity and diversity of this ecosystem.

Keywords: Plankton, trophic-dynamics, Coquimbo, upwelling, marine reserve, Chañaral de Aceituno Island.