Plasticity in dormancy behaviour of Calanoides acutus in Antarctic coastal waters

Tristan E G Biggs,David W Pond,Claire Evans,Corina P D Brussaard,Hugh J Venables

doi:10.1093/icesjms/fsaa042

Abstract

Abstract Copepods that enter dormancy, such as Calanoides acutus, are key primary consumers in Southern Ocean food webs where they convert a portion of the seasonal phytoplankton biomass into a longer-term energetic and physiological resource as wax ester (WE) reserves. We studied the seasonal abundance and lipid profiles of pre-adult and adult C. acutus in relation to phytoplankton dynamics on the Western Antarctic Peninsula. Initiation of dormancy occurred when WE unsaturation was relatively high, and chlorophyll a (Chl a) concentrations, predominantly attributable to diatoms, were reducing. Declines in WE unsaturation during the winter may act as a dormancy timing mechanism with increased Chl a concentrations likely to promote sedimentation that results in a teleconnection between the surface and deep water inducing ascent. A late summer diatom bloom was linked to early dormancy termination of females and a second spawning event. The frequency and duration of high biomass phytoplankton blooms may have consequences for the lifespan of the iteroparous C. acutus females (either 1 or 2 years) if limited by a total of two main spawning events. Late summer recruits, generated by a second spawning event, likely benefitted from lower predation and high phytoplankton food availability. The flexibility of copepods to modulate their life-cycle strategy in response to bottom-up and top-down conditions enables individuals to optimize their probability of reproductive success in the very variable environment prevalent in the Southern Ocean.

Highlights

Lipid-rich copepods are important conduits of carbon flow from the base of the marine food web to higher trophic levels and support fish, mammal and seabird communities (Pervushin, 1968; Hopkins and Torres, 1989; Voronina, 1998)
Two main periods of phytoplankton accumulation occurred in S1 (2012–2013), 30 November–2 January and 11 February–15 April (Figure 2), as indicated by chlorophyll a (Chl a) dynamics, which were dominated by diatoms (86 6 14% n 1⁄4 13 and 88 6 19% n 1⁄4 17, of total Chl a, respectively; Biggs et al, 2019)
Chl a concentrations had been increasing for 2 weeks prior to vertical migration events (VMEs) 3 and a high biomass phytoplankton bloom developed over a period of 2 months (Figure 2)

Summary

Introduction

Lipid-rich copepods are important conduits of carbon flow from the base of the marine food web to higher trophic levels and support fish, mammal and seabird communities (Pervushin, 1968; Hopkins and Torres, 1989; Voronina, 1998). The life cycles of copepods are strongly affected by this distinct seasonality, and they have developed specific adaptations to take advantage of short-term food availability to survive long periods of VC International Council for the Exploration of the Sea 2020. Little is known about the life span of overwintered late stage copepodites with some studies suggesting a 1 year life cycle (Marin, 1988; Atkinson et al, 1997) whilst others suggest that individuals may re-enter dormancy and survive an extra year (Drits et al, 1994; Hagen and Schnack-Schiel, 1996)

Methods

Results

Discussion

Conclusion