Satellite observation of the winter variation of sea surface temperature fronts in relation to the spatial distribution of ichthyoplankton in the continental shelf of the southern East China Sea

The wintertime variations and distributions of sea surface temperature (SST) and thermal fronts associated with the spatial distribution of ichthyoplankton were investigated in the continental shelf waters of the southern East China Sea (ECS) by using 10year (2005-2015) satellite SST images with an entropy-based edge detection method. The Mainland China Coastal Front and Kuroshio Front (KF) in winter (December to March) were examined with SST gradient magnitudes (GMs) of 0.20-0.40 and 0.30-0.45 degrees C Km(-1), respectively, along the 50m and 100-200m isobaths in the southern ECS. These two fronts coincided with isotherms of 14-16 degrees C and 21-22 degrees C, respectively. The Mainland China Coastal Front pattern remained fairly stable along the 50m isobaths, and the coexisting SST front and upwelling were shifted seaward or shoreward with the recession or intrusion of the KF during the winters. Notably, the SST GMs of the KF showed a significant strengthening that was higher than those of the past two decades. Moreover, the total abundance of the nearshore waters of the KF (which was occupied by approximately 75% neritic species) was 23 times higher than that of the offshore waters (which was occupied by approximately 63.60% oceanic species). We suggest that the generation of the KF in winter may act as the biological barrier of oceanic organisms and larval fishes in the study area.