Abstract
In this study, we investigate the distribution of calanoid copepod eggs in the sediments of Masan Bay (South Sea, Korea), in which hypoxic conditions occur every summer. In August (2011), hypoxia was observed at all stations, while normoxia was observed in April (2012). The pH and hydrogen sulphide concentration at the sediment-water interface in the inner bay during August were 7.7 and >20 mol L−1, respectively, and there was no significant difference between the stations in April. The abundance of eggs in the sediment ranged from 0.69 to 1.49 × 106 eggs m−2 in August, and from 0.59 to 1.08 × 106 eggs m−2 in April. Notably, the proportion of abnormal eggs was high (a maximum of 77.1%) in August, and a uniform distribution of normal eggs (>80%) was observed in April. A generation of abnormal eggs hatched with deformed nauplii in Masan Bay during the summer, and a failure to hatch was likely due to the high H2S concentration and low pH caused by hypoxia. In this paper, we discuss the effects of hypoxia and seabed environments on the hatching success of calanoid copepod eggs.
Highlights
Eutrophication is a problem that persists in coastal waters worldwide, including those in Korea, Masan Bay [1]
Oxygen-deficient sediments are frequently associated with the formation of hydrogen sulphide (H2 S), which is toxic to most benthic organisms [3]
The purpose of this study is to investigate the environmental factors of the seabed and the copepod egg abundance to evaluate the effect of hypoxia on the copepod egg hatching rate in Masan Bay, wherein hypoxia is widespread during the summer
Summary
Eutrophication is a problem that persists in coastal waters worldwide, including those in Korea, Masan Bay [1]. Oxygen-deficient sediments are frequently associated with the formation of hydrogen sulphide (H2 S), which is toxic to most benthic organisms [3]. The equilibrium concentration of different sulphide species (i.e., H2 S, HS− , and S2− ) varies with the pH. The pH of natural seawater ranges from 7.9 to 8.3, and HS− is dominant. In pore water, where the pH can be as low as 6.0–6.5, the dominant species is H2 S [4,5]. The toxicity of sulphide to marine benthic organisms is controlled by pH, and it increases with a decrease in pH [4]
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