Lipid storage consumption and feeding ability of Calanus glacialis Jaschnov, 1955 males

Maja Hatlebakk,Martin Graeve,Lauris Boissonnot,Janne E Søreide

doi:10.1016/j.jembe.2019.151226

Abstract

Calanus is one of the best studied genera of Arctic zooplankton, but still we know very little about the males since they are short-lived and mainly present in winter. Their short life-span compared to females is assumed to be a combination of high mating activity, no feeding and consequential depletion of lipid stores. In this study we tested 1) if the life span of male Calanus glacialis is limited by their lipid storage reserves and 2) if males are capable of feeding and utilize food if present. We ran two separate experiments from January to March; one on starvation and one on feeding. In the 39-days long starvation experiment we followed the lipid sac size of individually incubated males until their time of death. On average the total lipid (TL) content decreased by 2.6 to 4.5 μg day−1, but despite this males had substantial amounts of lipids left (131.4 μg, SD 44.0) when they died. This strongly suggests that the depletion of lipid reserves is not the main reason for males' short life span which in this study was measured to be up to 73 days. In the feeding experiment, we fed both C. glacialis males and females ad libitum with 13C labelled microalgae. Both males and females were capable of feeding and assimilate the diatom monoculture, but females responded faster to the sudden favourable food conditions, and produced more and larger fecal pellets than the males. Assimilation of 13C labelled 20:5(n-3), an essential polyunsaturated fatty acid (PUFA), from the diatom diet was traceable in both males and females on day 21, and then with a higher enrichment in females than males. Morphological investigations of the feeding appendages showed some differences between sexes, suggesting males to be more omnivorous than females. In conclusion, lipid storage depletion is not the cause of death for male C. glacialis, and males may even compensate for some of the mating energy costs by feeding. In future, we recommend further studies on the role of essential fatty acids (FA) for sperm formation and aging as determining factors for males' relatively short life span.

Highlights

The mesozooplankton community of Arctic and Sub-Arctic seas, in terms of biomass, are dominated by copepods of the genus Calanus (Kosobokova and Hirche, 2009)
C. hyperboreus are only found in low numbers in Svalbard fjords (Scott et al, 2000; Arnkværn et al, 2005), we focused on C. glacialis in this study
These were not included in the calculations since we could not rule out the effect of handling as cause of death

Summary

Introduction

The mesozooplankton community of Arctic and Sub-Arctic seas, in terms of biomass, are dominated by copepods of the genus Calanus (Kosobokova and Hirche, 2009). Copepods have developed three different foraging strategies: ambush feeders which waits passively for prey to come within range (Kiørboe et al, 2009), cruise feeders which encounter and catch prey as they swim through the water (Kjellerup and Kiørboe, 2011) and feeding-current feeders which create a feeding current and harvest their catch in the current (Koehl and Strickier, 1981). The passive ambush feeders have lower risk of being eaten, but at the cost of lower feeding efficiency (Henriksen et al, 2007; Kiørboe et al, 2010) while the active feeders benefit from high feeding efficiency, but at the cost of higher risk of encountering predators (Gonçalves et al, 2014; Van Someren Gréve et al, 2017).

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Conclusion