Climate-related changes in seasonal habitat pattern of Sthenoteuthis oualaniensis in the South China Sea

A habitat suitability index model (HSI) was established to examine seasonal habitat pattern of Sthenoteuthis oualaniensis in the South China Sea and assessed the impacts of the El Nino event on habitat variations based on sea surface temperature (SST), chlorophyll-a (Chla) and sea surface height (SSH). Environmental conditions and habitat patterns showed significant seasonal and spatial variations. Spatial pattern of favorable environmental conditions played important roles in regulating the ranges and longitudinal and latitudinal distributions of suitable habitats (areas with HSI >= 0.6) of S. oualaniensis across seasons. Significant positive correlation was found between SST and HSI, whereas negative relationship was revealed between HSI and Chla as well as SSH by correlation analysis. Comparing to normal climate condition in spring 2014, the El Nino events in spring 2015 and 2016 yielded lower SST and higher Chla and SSH, which were unfavorable for the formation of high-quality habitats. Favorable ranges of environmental conditions showed decreasing trend from spring 2014 to 2016. Consequently, the suitable habitats in spring 2015 and 2016 largely contracted and became discontinuity. Our findings indicated that seasonal habitat patterns of S. oualaniensis in the South China Sea were strongly affected by the El Nino events and local environmental conditions.