Accurate and timely quantification of widespread harmful algal bloom (HAB) distribution is crucial to respond to the natural disaster, minimize the damage, and assess the environmental impact of the event. Although various remote sensing-based quantification approaches have been proposed for HAB since the advent of the ocean color satellite sensor, there have been no algorithms that were validated with in-situ quantitative measurements for the red tide occurring in the Korean seas. Furthermore, since the geostationary ocean color imager (GOCI) became available in June 2010, an algorithm that exploits its unprecedented observation frequency (every hour during the daytime) has been highly demanded to better track the changes in spatial distribution of red tide. This study developed a novel red tide quantification algorithm for GOCI that can estimate hourly chlorophyll-a (Chl a) concentration of Cochlodinium (Margalefidinium) polykrikoides, one of the major red tide species around Korean seas. The developed algorithm has been validated using in-situ Chl a measurements collected from a cruise campaign conducted in August 2013, when a massive C. polykrikoides bloom devastated Korean coasts. The proposed algorithm produced a high correlation (R=0.92) with in-situ Chl a measurements with robust performance also for high Chl a concentration (300mg/m) in East Sea areas that typically have a relatively low total suspended particle concentration (<0.5mg/m).

The climate-induced changes in marine fishery resources in South Korea have been a big concern over the last decades. The climate regime shift has led to not only a change in the dominant fishery resources, but also a decline in fishery landings in several species. The habitat suitability index (HSI) has been widely used to detect and forecast fishing ground formation. In this study, the catch data of the Todarodes pacificus (Japanese Common Squid) and satellite-derived environmental parameters were used to estimate the HSI for the T. pacificus around South Korea. More than 80% of the total catch was found in regions with a sea surface temperature (SST) of 14.91–27.26 ℃, sea surface height anomaly (SSHA) of 0.05–0.20 m, chlorophyll-a of 0.32–1.35 mg m-3, and primary production of 480.41–850.18 mg C m-2 d-1. Based on these results, the HSI model for T. pacificus was derived. A strong positive relationship (R2 = 0.9260) was found between the HSI and the fishery landings. The climatological monthly mean HSI from 2002 to 2016 showed several hotspots, coinciding with the spawning and feeding grounds of T. pacificus. This outcome implies that our estimated HSI can yield a reliable prediction of the fishing ground for T. pacificus around South Korea. Furthermore, the approach with the simple HSI model used in this study can be applied elsewhere, and will help us to understand the spatial and temporal distribution of fishery resources.

Abstract:Our main objective in this study was to determine the inter-annual variation of the annual new production in the East/Japan Sea (EJS), which was estimated from MODIS-aqua satellite-derived sea surface nitrate (SSN). The new production was extracted from northern (>40 • N) and southern (>40 • N) part of EJS based on Sub Polar Front (SPF). Based on the SSN concentrations derived from satellite data, we found that the annual new production (Mean ± S.D = 85.6 ± 10.1 g C m −2 year −1 ) in the northern part of the EJS was significantly higher (t-test, p < 0.01) than that of the southern part of the EJS (Mean ± S.D = 65.6 ± 3.9 g C m −2 year −1 ). Given the relationships between the new productions and sea surface temperature (SST) in this study, the new production could be more susceptible in the northern part than the southern part of the EJS under consistent SST warming. Since the new production estimated in this study is only based on the nitrate inputs into the euphotic depths during the winter, new productions from additional nitrate sources (e.g., the nitrate upward flux through the MLD and atmospheric deposition) should be considered for estimating the annual new production.

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