A year-round study on digestive enzymes in the Arctic copepod Calanus glacialis: implications for its capability to adjust to changing environmental conditions

Abstract

43Zooplankton communities in Arctic shelf regions are dominated in terms of biomass by the calanoid copepod 44Calanus glacialis. During the winter months their metabolic rate decrease while they reside at deep water layers. 45In late winter, it migrates to the surface where the spring generation develops. To date, it is not fully understood 46what regulates the activity of the copepods and how it coincides with food availability. We sampled C. glacialis 47 in a high Arctic fjord in monthly intervals for a one year cycle and determined proteinase and lipase/esterase 48 activities in relation to food availability and depth distribution of the copepods. By substrate SDS-PAGE 49(sodium dodecylsulfate polyacrylamide gel electrophoresis), we tackled changes in specific isoforms. We found 50 clear seasonal enzyme activity patterns; activities of individuals in winter were reduced by at least 75 % as 51 compared to those feeding in spring. SDS-PAGE showed a high heterogeneity of lipolytic enzymes in C. 52glacialis, which reflects an extensive accumulation and metabolization of internal lipid. One band of proteolytic 53 activity was found and it intensified with the onset of the algal blooms. Females and younger developmental 54 stages showed high digestive enzyme activities when they resided in surface water and low activities when they 55 were in deep water. High enzyme activities were closely correlated to the onset of ice algae bloom in spring. 56However, the copepods descended in autumn even though food was still available. These results suggest that C. 57glacialis should be benefit from an earlier ice-break up on thus, earlier algal blooms in the season, but that the 58 copepods would not benefit from long lasting phytoplankton blooms.

Physiological acclimatization in high‐latitude zooplankton

“…Furthermore, chlorophyll a levels of large cells, the copepod's preferred food size (Dagg et al, 2009), differed by two orders of magnitude. One organismal response to food deprivation is the down‐regulation of digestive enzymes and their gene expression (Wang et al, 2006), which has been reported in copepods (Freese et al, 2016; Hassett & Landry, 1990; Mayzaud et al, 1992). Thus, not surprisingly, genes involved in digestion were differentially expressed in N .…”

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

“…Traditionally, Calanus copepods have been regarded as herbivores; however, their omnivore preferences (Cleary et al., 2017; Levinsen et al., 2000; Søreide et al., 2008; Yeh et al., 2020) and their ability to adjust to shifts in the timing and availability of their prey (Banas et al., 2016; Forest et al., 2011; Freese et al., 2016) can vary greatly. In addition, the complex hydrography (i.e., mixing of Atlantic, Arctic, and coastal water masses) around Svalbard significantly expands the pool of resources and niche diversity in terms of their habitat and diet (Kortsch et al., 2019).…”

“…An experimental study of the effects of temperature and food on C. finmarchicus and C. glacialis implies that the adaptation of C. glacialis to future warmer ocean conditions in the Arctic by spawning early will no longer be beneficial when C. finmarchicus matches the timing of gonad maturation with blooms (Kjellerup et al., 2012). Moreover, C. glacialis is probably not capable of exploiting longer periods of food availability in contrast to C. finmarchicus (Freese et al., 2016; Swalethorp et al., 2011). At the same time, the northward expansion of C. glacialis and its greater developmental rate are predicted to be an effect of increased primary production and decreased extent of ice in the central Arctic (Feng et al., 2018).…”

Spatial distributions of Southern Ocean mesozooplankton communities have been resilient to long‐term surface warming

“…A flexibility and responsiveness to changing environmental conditions allows species to optimize their performance over annual cycles. For instance, in the Arctic, Freese, Søreide, and Niehoff () found distinct seasonal oscillations in digestive enzyme activity in the copepod Calanus glacialis with much lower activity levels during winter, while Lischka, Giménez, Hagen, and Ueberschär () found differing seasonal patterns in digestive enzyme between two further Arctic copepod species, Pseudocalanus minutus and Oithona similis , with a spring activity peak in the former and a lower level of seasonal oscillation in the latter. The differing patterns of activity in each species reflect the diversity in their respective lifecycle strategies, both in terms of timing of reproduction and peak energy demand and their optimal diets.…”