The heterotrophy cultures reported a total EPA production of 2.7% of dry cell weight, 18 mg L−1 culture, a productivity of 1.3 mg L−1 day−1, which are promising values in the prospective of improving culture parameters for the biotechnological exploitation of dark cultivation. Photoautotrophic conditions led to a total EPA production of 1.6% of dry weight, 12.2 mg L−1 culture and productivity of 0.9 mg L−1 day−1. The marine diatom Cyclotella cryptica was cultivated for 14 days under photoautotrophic and heterotrophic conditions to define the effects on growth parameters, lipid production, total fatty acids and EPA content. Few species of diatoms are capable to grow in the dark using organic carbon sources. Marine diatoms are the major ecological producers of ω-3 fatty acids. Due to the high operation costs of photoautotrophic microalgae cultivation, heterotrophic growth represents a promising economic solution. Microalgae are considered a valuable and “green” source of EPA alternative to fish oils, but considerable efforts are necessary for their exploitation at an industrial level. Recently, the marketable value of ω-3 fatty acid, particularly eicosapentaenoic acid (EPA), increased considering their health effects for human consumption. However, the rate of detection of DCOIT was low because it degraded rapidly in the seawater before treatment for chemical analysis, except in the case of the treatment on the research vessel. Considering the NOECs, the environmental concentrations of these biocides suggest that the ecological risks posed by diuron and Irgarol are low, whereas those posed by DCOIT are high. The highest concentrations of diuron, Irgarol, and DCOIT in the environmental seawater in the Seto Inland Sea were 27.6, 3.2, and 24 ng/L, respectively. Compared to diuron and Irgarol, DCOIT exhibited a higher toxicity toward oyster embryos, and the minimum 24-h NOEC toxicity value for the oyster embryos was <3 ng/L. In recent years, the spat settlement of Pacific oysters has become poor, which presents a challenge for oyster aquaculture in Hiroshima Bay hence, we conducted embryotoxicity and larva settlement tests using Pacific oysters. We investigated the occurrence of antifouling biocides used worldwide including diuron, Irgarol 1051 (Irgarol), and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), which have been detected at sub-ppb levels in seawater in Japan, and estimated their no observed effect concentrations (NOECs). Hiroshima Bay is one of the most important oyster farming areas in Japan.
The Pacific oyster (Crassostrea gigas) is an important species in oyster farming worldwide, including in Japan. sustain the recruitment of oyster spat as an essential food. choctawhatcheeana was abundantly detected in the digestive tract of oyster larvae collected in the field, suggesting that Cyclotella spp. in sea water led to a successful larval settlement in both 20. The results of metabarcoding analysis indicated that increase in <10 μm size diatom Cyclotella spp. We also examined the species composition of 26.9 ☌ and chlorophyll a concentrations for 5 μg L⁻¹. In order to elucidate the favorable environmental window for oyster spat collection, we investigated water quality parameters (water temperature, salinity and nutrients), abundance of larval food and success of larval settlement during the period of spat collection in Hiroshima Bay. Rafted aquaculture using natural spat of the native oyster is conducted in this bay and spat collection during the spawning season in summer is a key process for sustainable farming.
Hiroshima Bay, located in the western part of the Seto Inland Sea, is the largest Pacific oyster Crassostrea gigas farming area in Japan.
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