The spatial-temporal consistency of chlorophyll-a and fishery resources in the water of the Zhoushan archipelago revealed by high resolution remote sensing

Abstract

Details of the chlorophyll-a (Chl-a) distribution in the water of the Zhoushan archipelago were analyzed based on data from the panchromatic multispectral sensor (PMS) of the GaoFen-6 (GF-6). A new Chl-a inversion model was built using in-situ Chl-a and the green-red bands of the 2 m spatial resolution GF-6/PMS image. Combined with fishery data, the relationship between Chl-a concentration and fish resources were revealed. The results show that: (1) High Chl-a concentration area was mainly concentrated in the nearshore intensive islands waters, and Chl-a concentration changes obviously with the change of tidal currents. Chl-a concentration around islands increases, especially downstream of islands. Seasonally, Chl-a concentration is higher in spring and summer, lower in autumn, and lowest in winter. (2) The change of fish eggs and larvae in the water of the Zhoushan archipelago shows consistency with the spatial distribution and seasonal variation of Chl-a. (3) The interaction between tidal currents and islands results in the diverse currents (upstream upwelling and downstream vortex currents) around the islands, promoting vertical water exchange and the uplifting of nutrients, resulting in a high overall Chl-a concentration in the waters around the islands. The diverse flow conditions, the ideal nutrient-rich environment, and the abundant phytoplankton attract a large number of fish to gather and breed in the waters around the islands. (4) Chl-a of intensive island waters is an essential indicator for fish spawning grounds.

Study of the Response of Environmental Factors of the Coastal Area in Zhoushan Fishery to Typhoon In-fa Based on Remote Sensing

“…In-fa induced Ekman pumping significantly contributed to the rise in SSS, while rainstorms and changes in currents efficiently decreased SSS; this is a phenomenon that has also been observed in other nearshore seas [33,58,61] Previous studies [46,62,63] have shown that Chl-a concentrations are higher in the coastal area of Zhoushan Fishery in summer (Figure 6(a1,a2)), which is probably due to the rich nutrients carried by the Yangtze diluted water, coastal upwelling, and sufficient sunlight. The maximum Ch1-a concentration usually occurs at the surface or subsurface layers, and the concentration decreases with depth [62].…”

“…Previous studies [46,62,63] have shown that Chl-a concentrations are higher in the coastal area of Zhoushan Fishery in summer (Figure 6(a1,a2)), which is probably due to the rich nutrients carried by the Yangtze diluted water, coastal upwelling, and sufficient sunlight. The maximum Ch1-a concentration usually occurs at the surface or subsurface layers, and the concentration decreases with depth [62].…”

“…This product includes daily and monthly averaged data on global ocean biogeochemical parameters. To assess the suitability of the Chl-a reanalysis product within the coastal area of Zhoushan Fishery, we compared it with the surficial in situ Chl-a data gathered on 23-24 October 2019 [46] and the CMEMS Chl-a data (Figure 1). We calculated the spatial average for the 4 km region surrounding each in situ location.…”

“…Previous studies have shown a strong correlation between changes in the biomass density of fish eggs and larvae and variations in Chl-a concentration in the water [46], indicating that Chl-a is a reliable indicator of phytoplankton biomass and the prior status of the aquatic food chain [69]. Additionally, Chl-a levels can influence the fertility of waters and help evaluate the potential productivity of fishing grounds [70,71].…”

Monitoring Dissolved Oxygen Concentrations in the Coastal Waters of Zhejiang Using Landsat-8/9 Imagery

“…The models were evaluated using R 2 and adj-R 2 values (Table 1), showing the best-fit models under different independent variable inputs. The results indicated that the model had a significant response to the blue (Rrs_483) and red (Rrs_613, Rrs_655) bands of Landsat imagery, which are also commonly used to establish statistical relationships with the Chl-a and TSM concentrations [36][37][38]. Therefore, the model can explain the impact of SST on the DO concentration and reflects the relationships among the Chl-a, TSM, and DO concentrations to a certain extent, offering good interpretability and practical significance.…”