Mortality of Calanus helgolandicus: Sources, differences between the sexes and consumptive and nonconsumptive processes

Jacqueline L Maud,Angus Atkinson,Andrea J Mcevoy,Penelope K Lindeque,Andrew G Hirst

doi:10.1002/lno.10805

Abstract

AbstractWhile losses from mortality are as important as gains from reproduction in zooplankton population dynamics, the former are more challenging to quantify. We used two approaches to provide complementary insights into the mortality of a biomass‐dominant copepod, Calanus helgolandicus, at Station L4 in the English Channel. Using a neutral‐red staining method, we found that dead carcasses represented a mean of 9% of the C. helgolandicus copepodites sampled. The resulting nonconsumptive mortality rates are the first that have been derived for C. helgolandicus; and estimates suggest a contribution of 0–54% (median of 4.4%) to the total mortality rate. Consumptive mortality (i.e., that due to removal by predation), dominated for most of the year and contributed a mean of 89% to total mortality. Nonconsumptive mortality increased during summer and winter, and was positively related to maximum wind speed during the preceding 72 h, indicating that extreme weather events may lead to increased mortality. Using the Vertical Life Table approach, mortality rates across the CV‐adult male stage pair were on average ∼ 2.5 times greater than those of CV‐adult females. Adult male consumptive mortality rates were ∼ 6 times greater than those for females; adult male nonconsumptive rates were twice those of females, suggesting that predation is of greater significance to male loss rates. Summer CV‐adult mortality rates were positively correlated to temperature, and to the abundance of predatory chaetognaths and siphonophores, suggesting that the gelatinous predator assemblage is the dominant agent for population control of late stage copepodites of C. helgolandicus at L4.

Highlights

While losses from mortality are as important as gains from reproduction in zooplankton population dynamics, the former are more challenging to quantify
Calanus helgolandicus reproduction appears to occur throughout the year at L4, as CI to CV stages were present through most months, except for the winter when there was an increase in the abundance of CV stages and adult females (Fig. 1b)
Mortality was calculated over various temporal scales, including over 4 yr (CV-adult Vertical Life Table (VLT)) and seasonal over 1 yr

Summary

Introduction

While losses from mortality are as important as gains from reproduction in zooplankton population dynamics, the former are more challenging to quantify. While the consumption of a copepod by most predators typically involves the removal of the entire animal from the water column, including consumption by fish, fish larvae, jellyfish, and chaetognaths (Bonnet et al 2005, 2010), other copepod species (Daan et al 1988; Boersma et al 2014), and even via cannibalism (Bonnet et al 2004); nonconsumptive mortality, that is mortality not caused by predation, tends not to lead to the immediate removal of the body of the animal, and typically results in a carcass This nonconsumptive mortality can result from death from old age (Rodr ıguezGran~a et al 2010), disease, and parasitism (Kimmerer and McKinnon 1990), the ingestion of toxic prey (K^a et al 2014), Mortality of Calanus helgolandicus exposure to environmental pollutants (Cohen et al 2014; Wendt et al 2016), and physical stresses such as during extreme weather events (Dubovskaya et al 2005; Bickel et al 2011; Tang et al 2014)

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Conclusion