## 4 Discussion
### Key Environmental Factors of the Habitat of Krill and Their Impacts
The average monthly contribution rates of SSH and SST are both approximately 10%. Although their influence is relatively limited, they can change the marine hydrological conditions, thereby affecting the distribution of phytoplankton and the physico-logical adaptability of krill and further regulating the habitat suitability. SSH mainly affects the distribution of phytoplankton by changing the ocean currents and water body structure. Its annual variation range is small, with an adaptation range of \(-\)3.43 to \(-\)2.9 m, a peak suitable range of \(-\)3.41 to \(-\)2.91 m, and the environmental response curve shows a trend of rising first and then falling. SSH is related to the water depth. The hydrological environment in deep waters is complex, and krill have weak swimming abilities and are easily affected by hydrological dynamic factors such as ocean currents and eddies. For example, mesoscale eddies may become suitable habitats for krill due to their high primary productivity [6]. Small fluctuations in SST can have a significant impact on the physiological status of Antarctic krill. The suitable SST varies in different sub-regions. The suitable SST in sub-region 48.1 is \(-\)1.78 to 0.73 \({}^{\circ}\)C, with a peak suitable range of \(-\)1.75 to \(-\)0.54 \({}^{\circ}\)C; the suitable SST in sub-region 48.2 is \(-\)1.81 to 1.98 \({}^{\circ}\)C, with a peak suitable range of \(-\)1.61 to 1.4 \({}^{\circ}\)C; the suitable SST in sub-region 48.3 is \(-\)0.18 to 1.29 \({}^{\circ}\)C, with a peak suitable range of 0.34 to 1.03 \({}^{\circ}\)C. Under low temperature conditions, the probability of species occurrence shows an upward trend, while it shows a downward trend at relatively high temperatures. The suitable SST in each sub-region is consistent with the research results of [PERSON] [43], but the peak range is smaller than that in [PERSON]'s research. This may be due to the natural fluctuations of the marine environment between different years and the differences in the operation modes of the vessels. SIC shows an obvious seasonal influence, with an average monthly contribution rate usually only 7.6%, but in late autumn and winter (from May to August), this contribution rate will increase to 13.5%, with a suitable range of 0-75.92% and a peak suitable range of 0-27.73%. Its dynamic changes not only contribute to the growth of phytoplankton but also provide a sheltering effect for krill habitats, especially during the critical stages of krill reproduction and growth. Its environmental response curve shows an upward trend when SIC is at a relatively high level, which is consistent with the research results of [PERSON] (2018) and others. However, as SIC continues to rise, the environmental response curve shows a downward trend. This may be because SIC poses a danger to ships, causing them to actively stay away from areas with high SIC density for fishing operations, thus leading to a decrease in environmental adaptability ([PERSON], 2018). SSS plays a key role in providing long-term guarantees for the physiological metabolism and reproductive activities of krill, with an average monthly contribution rate of up to 9.9%. It is worth noting that the differences in SSS in different seasons and different sub-regions are relatively small, with a suitable range of 33.61-34.69% and a peak suitable range of 33.82-34.29%, and the corresponding environmental response curve shows a trend of rising first and then falling, which is consistent with the research results of [PERSON] and others (2018). Ship position factors and policy factors also have a certain impact on the habitat selection and distribution patterns. Fishing vessels usually avoid entering quota areas or areas with high SIC density due to fishing quotas or to avoid the dangers posed by SIC, thus affecting the development and utilization of habitats.