# Spatial and Environmental Drivers of Summer Growth Variability and Adaptive Mechanisms of Euphausia crystallorophias in the Amundsen Sea and Its Adjacent Regions

## TL;DR

This study explores how environmental factors like temperature and sea ice affect the growth of ice krill in the Amundsen Sea and surrounding areas.

## Contribution

The study reveals new insights into how ice krill adapt their growth strategies in response to environmental variability in the Antarctic.

## Key findings

- Ice krill in warmer, productive waters grow longer, while those in colder, less productive areas store more energy.
- Growth patterns are influenced by factors like sea surface temperature, salinity, and sea ice concentration.
- Krill in the Amundsen Sea show higher structural growth, while those in transitional zones prioritize body condition.

## Abstract

Ice krill are a key component of the Antarctic food web, but scientists still lack a full understanding of how different environmental conditions affect their growth. This study focused on the Amundsen Sea and adjacent Antarctic waters to examine how water temperature, salinity (saltiness), sea ice cover, and location influence ice krill growth in summer. The researchers found that environmental differences led to noticeable changes in krill growth. For example, in slightly warmer waters with abundant food (often near melting sea ice), ice krill grew faster and increased in length. In colder conditions with less food available, they gained weight (stored energy) instead of growing longer. This demonstrates that ice krill can adjust their growth strategy in response to different environmental conditions. Understanding this flexibility is important because it helps scientists predict how krill and the Antarctic ecosystem will respond to a warming climate and changing sea ice conditions. Ice krill are a vital food source for penguins, seals, and whales, and they also help store carbon in the ocean. Therefore, understanding their growth helps us anticipate broader effects of climate change in Polar Regions.

Ice krill (Euphausia crystallorophias) play a key role in the Antarctic coastal ecosystem, yet its spatial growth variability remains poorly understood. This study examined 5298 krill individuals from 52 stations across the Amundsen Sea, transitional waters, and the Ross Sea, collected between 2020 and 2024. Length–weight relationships (LWR) were constructed to derive the condition factor a and the allometric growth exponent b, followed by regional comparisons and environmental response analyses using boxplots, redundancy analysis (RDA), and generalized additive models (GAM). Boxplots revealed that a was significantly higher in the Amundsen Sea and transitional zone than in the Ross Sea, while b was highest and most variable in the Amundsen Sea. RDA indicated that a was primarily associated with depth, latitude, mean temperature, and mean salinity, whereas b was influenced by sea surface temperature, chlorophyll-a, sea ice concentration, and longitude. GAM further showed nonlinear responses of a to mean temperature, mean salinity, and depth, with peaks near −0.5 °C, 34.2 PSU, and 3500 m, respectively. These results suggest that krill in deep, cold, and less-productive transitional zone allocate more energy to body condition (high value a), while those in warmer, moderately productive regions like the Amundsen Sea invest more in structural growth (high value b). This study provides new insights into the environmentally driven growth strategies of ice krill and contributes to understanding its ecological adaptability under changing climatic and oceanographic conditions.