New insights into the biology of Calanus spp. (Copepoda) males in the Arctic

Abstract

Adult males of <i>Calanus</i> copepods in the Arctic are mainly observed between late autumn and late spring, and are seldom recorded during summer. Due to logistical constraints, there are still relatively few studies on zooplankton in high-latitude regions during the winter, and subsequently, little is known about <i>Calanus</i> males. Here, we present data on abundance, spatial distribution, prosome length, lipid content, respiration and swimming activity of i>Calanus</i> adults, along with adult sex ratios in i>Calanus</i> populations from 5 Arctic fjords in Svalbard, Norway (78-80° N) during the polar night in January 2015, 2016 and 2017. Adult males and females of i>Calanus</i> were observed at all locations and occurred throughout the entire water column. Morphological examination and molecular identification of i>Calanus</i> males proved that all males encountered belong to <i>Calanus glacialis</i>, even in the fjords where overwintering copepodite stage CV of <i>C. finmarchicus</i> dominated at the time. Adult sex ratios in <i>C. glacialis</i> populations varied from 1 male per 4 females to 2 males per female. From 3 to 18% of females carried spermatophores attached to the genital segment. Lipid content in males was slightly higher than in females. Shipboard experiments showed that males had higher swimming activity and respiration rates than females. Our observations indicate that adult males of <i>C. glacialis</i> stay active and demonstrate active mating behavior in mid-winter, and that the mating phenology of <i>C. glacialis</i> is decoupled from that of <i>C. finmarchicus</i> in the study area in January.