Influence of intensive net cage farming on hydrodynamic and geochemical environmental conditions and the mass mortality of abalone in South Korea.

The abalone aquaculture industry in South Korea has grown rapidly since the 2000s. In this study, we investigated the sedimentary pollution at four major abalone farms responsible for ~60% of all South Korean abalone produced. We also surveyed the current statuses of cage facilities, abalone mass mortality, and current velocities within and outside farm cages. The concentrations of total organic carbon in the study area were 7.92 ± 2.09 mg g-1, indicating a mild level of sedimentary pollution. We observed higher mortality rates in rectangular-shaped shelter cages than in triangular shelters. With increases in the number and size of abalone farming facilities, current velocities inside the cages declined by an average of 45% relative to those outside the cages, leading to poor habitat conditions for farmed abalone. Our results provide insights into the current status of the benthic environments and major causes of mass mortality in the abalone farms of South Korea.

Toxicity of dietary selenomethionine in juvenile steelhead trout, Oncorhynchus mykiss: tissue burden, growth performance, body composition, hematological parameters, and liver histopathology.

The steelhead trout (Oncorhynchus mykiss) is the species most at risk from selenium (Se) exposure in the San Francisco Bay Delta (SFBD). However, although steelhead trout are usually exposed to environmental Se in the juvenile stage, data to test their sensitivity to excess Se, especially its organic form, in the juvenile stage are scarce. Therefore, the objective of the current study was to assess the sensitivity of juvenile steelhead trout to ecologically relevant forms of Se using integrated sensitive endpoints. Fish (mean weight: 22.3 g) were fed one of five diets containing 1.1 (control), 8.8, 15.4, 30.8, and 61.6 µg Se/g diet dw (Se1.1, Se8.8, Se15.4, Se30.8, and Se61.6, respectively) in the form of selenomethionine for 4 weeks. After 4 weeks, Se significantly accumulated in a dose-dependent manner in all tissues at different rates. The growth rate and plasma cholesterol were significantly depressed in fish fed diets containing Se30.8 and above. Hematological parameters and mortality were significantly elevated in fish fed the Se61.6 diet. Marked histopathological alterations were observed in fish fed the Se8.8 diet (the lowest observed effect concentration, LOEC) and above. The current results suggest that the steelhead trout is more sensitive to excess Se than nonanadromous rainbow trout used in previous studies because of its lower LOEC despite the use of selenomethionine and the shorter experimental duration. Additionally, it should be noted that the current Se levels found in the SFBD are already a threat to the threatened population of steelhead trout on the central California coast.

Evaluation of phytoplankton community composition in the eutrophic Masan Bay by HPLC pigment analysis.

To assess the spatiotemporal changes in phytoplankton community composition in relation to the environment of Masan Bay, a semi-enclosed bay on the southern coast of Korea, photosynthetic pigments and environmental variables were analyzed in seawater, every month between March and November 2010. The level of dissolved inorganic nutrients was highest between July and September when the freshwater influx was at its peak, whereas chlorophyll a level was highest in April and August. Phosphate concentration was low in April (average: 0.22 +/- 0.17 microM), indicating the role of phosphate as a growth-limiting factor for phytoplankton. The results of pigment analysis indicate that dinoflagellate blooms occurred under favorable conditions, where competition with diatoms occurred. Fucoxanthin- and chlorophyll b-containing phytoplankton dominated the surface layer of Masan Bay from July to September. The composition of phytoplankton community in Masan Bay changed dramatically each month according to variations in the amount and composition of nutrients introduced through surface runoff.