Influence of the lunar cycle on the variability of the copepod community in subtropical waters

Abstract

Zooplankton abundance, biomass, and taxonomic composition are parameters of paramount importance to study marine ecosystems. Also, their variability in relation to water column properties such as temperature or salinity is of importance to know their development and ecosystem changes. In this study, we analyzed the temporal variability of the copepod community in subtropical waters north of Gran Canaria during the Late Winter Bloom (LWB) period and its relationship with the lunar cycle, focusing on a seven-month sampling period. Weekly sampling in the epipelagic layer (0–200 m) was conducted from November 2010 to June 2011and it was analyzed at two oceanic stations. Abundance was obtained using a digital image classification method, with a taxonomic emphasis on copepods from the orders Cyclopoida (genera Oithona, Sapphirina; families Corycaeidae, Sapphirinidae, Oncaeidae), Harpacticoida, and Calanoida. From this data, we estimated biomass and individual biomass for the different taxonomic groups. As expected, we found an increase in biomass and abundance of most groups (e.g., Calanoida) during the LWB. By contrast, the genus Oithona exhibited an opposite pattern, decreasing during the LWB. We also observed a relationship of some copepod groups with the lunar cycle as the effect of reduced predation pressure from diel vertical migrants during the illuminated phase of the moon. Although Calanoida was the dominant group, its response to the lunar cycle was less pronounced compared to Oithonidae, Oncaeidae, or Harpacticoidae. This study underscores the influence of the lunar cycle on copepod dynamics, providing additional information about how these organisms interact with predation pressure from diel vertical migrants in the ocean.