In a comfort zone and beyond-Ecological plasticity of key marine mediators.

Emilia Trudnowska,Thomas Brown,Joanna Stoń-Egiert,Marta Gluchowska,Irina Smolina,Kaja Balazy

doi:10.1002/ece3.6997

Abstract

Copepods of the genus Calanus are the key components of zooplankton. Understanding their response to a changing climate is crucial to predict the functioning of future warmer high‐latitude ecosystems. Although specific Calanus species are morphologically very similar, they have different life strategies and roles in ecosystems. In this study, C. finmarchicus and C. glacialis were thoroughly studied with regard to their plasticity in morphology and ecology both in their preferred original water mass (Atlantic vs. Arctic side of the Polar Front) and in suboptimal conditions (due to, e.g., temperature, turbidity, and competition in Hornsund fjord). Our observations show that “at the same place and time,” both species can reach different sizes, take on different pigmentation, be in different states of population development, utilize different reproductive versus lipid accumulation strategies, and thrive on different foods. Size was proven to be a very mutable morphological trait, especially with regard to reduced length of C. glacialis. Both species exhibited pronounced red pigmentation when inhabiting their preferred water mass. In other domains, C. finmarchicus individuals tended to be paler than C. glacialis individuals. Gonad maturation and population development indicated mixed reproductive strategies, although a surprisingly similar population age structure of the two co‐occurring species in the fjord was observed. Lipid accumulation was high and not species‐specific, and its variability was due to diet differences of the populations. According to the stable isotope composition, both species had a more herbivorous diatom‐based diet in their original water masses. While the diet of C. glacialis was rather consistent among the domains studied, C. finmarchicus exhibited much higher variability in its feeding history (based on lipid composition). Our results show that the plasticity of both Calanus species is indeed impressive and may be regulated differently, depending on whether they live in their “comfort zone” or beyond it.

Highlights

The fundamental way by which organisms cope with climate change is through ecological plasticity, which encompasses any type of environmentally induced change
Copepods of the genus Calanus are the key components of zooplankton in the Arctic and northern Atlantic waters (Aarflot et al, 2017; Carstensen et al, 2019; Jaschnov, 1970), and they play a crucial role in marine food webs as the main mediators between the microbial system, phytoplankton, and higher trophic levels
Such knowledge would be of great importance to verify and extend many existing models aimed at predicting the future of the Arctic ecosystem based on Calanus ecology (Banas et al, 2016; Bandara et al, 2019; Feng et al, 2018; Ji et al, 2012; Melle et al, 2014; Renaud et al, 2018)

Summary

Introduction

The fundamental way by which organisms cope with climate change is through ecological plasticity, which encompasses any type of environmentally induced change (e.g., morphological, physiological, behavioral, phenological). Zooplankton can respond to global environmental changes phenotypically (with alterations in their physiology or behavior) or evolutionarily (with a shifting genetic composition of populations) (Dam, 2013; Kelly et al, 2017) It is still not known whether marine species will have the capacity to adjust to ongoing changes through phenotypic plasticity in the short term or adapt in the longer term (Byrne et al, 2020). Copepods of the genus Calanus are the key components of zooplankton in the Arctic and northern Atlantic waters (Aarflot et al, 2017; Carstensen et al, 2019; Jaschnov, 1970), and they play a crucial role in marine food webs as the main mediators between the microbial system, phytoplankton, and higher trophic levels. Due to problems with proper Calanus species identification, knowledge about their ecological plasticity and functioning in various oceanic conditions is still very limited

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