| Antarctic krill,usually referred to Euphausia superba,is a large perennial crustacean with a certain swimming ability.It mainly feeds on plankton on the sea surface,such as algae and small plankton.Krill has become an important food source for top predators such as penguins,seabirds,and seals in the Southern Ocean ecosystem due to its abundant resources,and plays a key role in the Southern Ocean ecosystem.As the most important form of fishery in the Southern Ocean at present,although the development of krill fishery is restricted due to ecological considerations,it still has huge exploitation potential.As countries pay more and more attention to the strategic position of Antarctica and increase scientific research investment,the study on krill has become the focus and hotspot of Antarctic ecological study.There are many early or traditional research methods,including regression analysis,correlation analysis,discriminant analysis,principal component analysis,etc.,but with the continuous improvement in understanding of marine ecology and the continuous improvement of the requirements for the depth and accuracy about marine animal research,the spatial relationship has received more and more attention from researchers.Compared with traditional statistical methods,spatial statistics integrates geographic spatial relationships into mathematical statistics,which makes up for the limitations of the random independence assumption of traditional statistics,and helps researchers to solve problems by using universally connected methods.In the process of developing krill fishery,determining its resource distribution pattern and its changes has become an important research field.However,due to the vary spatial-temporal dynamics of krill resources,the current study on its resource distribution has not made great progress,which includes the spatial and temporal scale of resource distribution.For this reason,based on the krill density data from 1926 to 2016,this study conducted a hotspot analysis on the spatial and temporal distribution of krill resources around Antarctica,and analyzed the temporal and spatial changes in hotspots and coldspots.On this basis,the krill resource density data was interpolated into 10 spatial scales,and the relationship between the krill resource density and the spatial scale was calculated using linear,logarithmic,exponential,power-law and polynomial functions.The variations of centroid in hotspot(coldspot)areas at different spatial scales were also analyzed,and a multi-scale analysis is carried out on the Antarctic Peninsula which is the main distribution area of krill resources.On the one hand,understanding the long-term changes in the temporal and spatial patterns of krill resources around the Antarctic can provide basic information for the study of krill fisheries.On the other hand,the understanding of the scale effect of krill distribution can provide useful ideas and scientific advice for further study on the temporal and spatial distribution of krill.The main conclusions drawn in this study are summarized as follows,(1)There was one core hotspot area,one sub-hotspot area and one edge hotspot area from 1926 to 1935 and from 1936 to 1945;one core hotspot area,one sub-hotspot area and one edge hotspot/coldspot area from 1976 to 1985;two core hotspot areas,two subhotspot areas,two edge hotspot areas,one sub-coldspot area and one coldspot area from1986 to 1995;two core hotspot areas,two sub-hotspot/sub-coldspot areas and two edge hotspot/coldspot areas from 1996 to 2005,;and from 2006 to 2016,there are two subhotspot areas,two edge hotspot areas,one sub-coldspot area and one edge coldspot area,respectively.Those hotspots/coldspots mostly occurred in the South Sandwich Islands,the Antarctic Peninsula and the west of the Prydz Bay.During the study period(1926-2016),krill abundance,the percentage of krill abundance in the hotspot area and the size of hotspot area had generally reduced,but the percentage of krill abundance in coldspot area and the size of coldspot area were increasing,while krill abundance in coldspot area decreased.It is a feasible approach to build an irregular triangle network to measure the size of hotspot/coldspot area and utilize hotspot analysis with 95% confidence to analyze the spatial-temporal patterns of krill distribution.(2)There was a significant scaling relationship between the maximum,the skewness,kurtosis,the Coefficient of Variation(CV)of global krill density and the spatial scale.Significant scaling relationship between the maximum,skewness,kurtosis,third quartile(Q3),and CV of the krill density in hotspot area and the spatial scale was found.A significant scaling relationship were also found between the maximum,mean,standard deviance(SD),skewness,kurtosis,Q3,CV and spatial scale for the coldspot area.The size of the hotspot(coldspot)area increased with the increasing of the spatial scale,and the offset of centroid indicated the locations of the hotspot(coldspot)area were greatly affected by the spatial scale.Significant shift of centroid for hotspot(coldspot)areas occurred when the spatial scale was greater than 1°×1°.Therefore,it is not recommended to use spatial scale that greater than 1° × 1° to identify the local spatial pattern for hotspot analysis of krill density.(3)The spatial pattern of krill is differed in spatial scales,and the density distribution of krill showed a clustering trend at 11 spatial scales.According to the correlogram between Moran’s I index and spatial scale,the characteristic spatial scales of krill density distribution were determined as 25 ′× 25 ′(the spatial scale that the value of Moran’s I index is across the line where y = 0)and 15 ′× 15 ′(the spatial scale is corresponding to the smallest value at the Moran’s I index is not different significantly from zero),respectively.It was suggested that 15 ′× 15 ′ could be the optimum spatial scale for studying the distribution of krill density in this region. |
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