NUTRIENT DECREASE IN THE SETO INLAND SEA, JAPAN, AND THE RESPONSE OF THE PHYTOPLANKTON ASSEMBLAGE TO THE DECREASE

The nutrient decrease in the eastern part of the Seto Inland Sea and its influence on the lower trophic levels of the coastal ecosystem are discussed based on the information obtained during our previous study. During the high economic growth from the 1960s onwards, the Seto Inland Sea became heavily eutrophicated. Since the enactment of the Law for Conservation of the Environment of the Seto Inland Sea in 1973, nutrient concentrations gradually decreased after 1970 and dissolved inorganic nitrogen (DIN) concentration in particular decreased after 1990. One fundamental explanation for the gradual decrease of DIN concentration from 1970 to the present is the enactment of the above law by the Environmental Agency. However, the reason for the recent decrease of DIN concentrations is still unknown. It was thought that the decrease of the upward nutrient flux across the overlying water-sediment interface greatly affected the water column nutrient concentrations. The response of phytoplankton assemblages to the decrease of nutrient concentrations seemed to be no apparent decrease of biomass but a change of species group and species composition.

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Influences of Nutrient Sources on the Alternation of Nutrient Limitations and Phytoplankton Community in Jiaozhou Bay, Southern Yellow Sea of China

Sustainability ◽

10.3390/su12062224 ◽

2020 ◽

Vol 12 (6) ◽

pp. 2224

Author(s):

Jie Shi ◽

Qian Leng ◽

Junying Zhu ◽

Huiwang Gao ◽

Xinyu Guo ◽

...

Keyword(s):

Atmospheric Deposition ◽

Phytoplankton Community ◽

Inorganic Nitrogen ◽

Marine Ecosystem ◽

Jiaozhou Bay ◽

Nutrient Concentrations ◽

River Input ◽

Aquaculture Wastewater ◽

The 1960S ◽

Yellow Sea Of China

A marine ecosystem box model was developed to reproduce the seasonal variations nutrient concentrations and phytoplankton biomasses in Jiaozhou Bay (JZB) of China. Then, by removing each of the external sources of nutrients (river input, aquaculture, wastewater discharge, and atmospheric deposition) in the model calculation, we quantitatively estimated its influences on nutrient structure and the phytoplankton community. Removing the river input of nutrients enhanced silicate (SIL) limitation to diatoms (DIA) and decreased the ratio of DIA to flagellates (FLA); removing the aquaculture input of nutrients decreased FLA biomass because it provided less dissolved inorganic nitrogen (DIN) but more dissolved inorganic phosphate (DIP) as compared to the Redfield ratio; removing the wastewater input of nutrients changed the DIN concentration dramatically, but had a relatively weaker impact on the phytoplankton community than removing the aquaculture input; removing atmospheric deposition had a negligible influence on the model results. Based on these results, we suppose that the change in the external nutrients sources in the past several decades can explain the long-term variations in nutrient structure and phytoplankton community. Actually, the simulations for the 1960s, 1980s, and 2000s in JZB demonstrated the shift of limiting nutrients from DIP to SIL. A reasonable scenario for this is the decrease in riverine SIL and increase in DIP from aquaculture that has reduced DIA biomass, promoted the growth of FLA, and led to the miniaturization of the phytoplankton.

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Dynamics of dissolved inorganic nitrogen and its effect on the discoloration of Porphyra yezoensis cultured along the eastern coast of Hiroshima Prefecture, the Seto Inland Sea

NIPPON SUISAN GAKKAISHI ◽

10.2331/suisan.76.849 ◽

2010 ◽

Vol 76 (5) ◽

pp. 849-854 ◽

Cited By ~ 5

Author(s):

OSAMU KAWAGUCHI ◽

HIDEYUKI TAKATSUJI

Keyword(s):

Inorganic Nitrogen ◽

Porphyra Yezoensis ◽

Seto Inland Sea ◽

Eastern Coast ◽

Dissolved Inorganic Nitrogen ◽

The Seto Inland Sea ◽

Hiroshima Prefecture

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Estimation of Benthic Fluxes of Dissolved Inorganic Nitrogen and Phosphorus from Sediments of the Seto Inland Sea.

Oceanography in Japan ◽

10.5928/kaiyou.7.151 ◽

1998 ◽

Vol 7 (3) ◽

pp. 151-158 ◽

Cited By ~ 9

Author(s):

Tamiji Yamamoto ◽

Osamu Matsuda ◽

Toshiya Hashimoto ◽

Hidekazu Imose ◽

Tomoaki Kitamura

Keyword(s):

Inorganic Nitrogen ◽

Seto Inland Sea ◽

Benthic Fluxes ◽

Dissolved Inorganic Nitrogen ◽

Nitrogen And Phosphorus ◽

The Seto Inland Sea

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Discovery of the fish host of the ‘planktonic’ caligid Caligus undulatus Shen & Li, 1959 (Crustacea: Copepoda: Siphonostomatoida)

Biodiversity Data Journal ◽

10.3897/bdj.8.e52271 ◽

2020 ◽

Vol 8 ◽

Author(s):

Susumu Ohtsuka ◽

Masaki Nawata ◽

Yusuke Nishida ◽

Masato Nitta ◽

Katsushi Hirano ◽

...

Keyword(s):

Life Cycle ◽

Adult Stage ◽

Species Group ◽

Fish Host ◽

Seto Inland Sea ◽

West Pacific ◽

The Seto Inland Sea

The siphonostomatoid copepod Caligus undulatus Shen & Li, 1959 has been widely reported from plankton samples obtained from neritic and oceanic waters off coasts of the Indo-West Pacific and Atlantic Oceans. Until now, its fish host has remained unknown. This copepod belongs to an intriguing group of congeners that, despite being part of a chiefly parasitic group, are consistently found as zooplankters. Quite unexpectedly, in October 2019, a fish host of C. undulatus was discovered in the Seto Inland Sea, Japan—namely, the Japanese sardinella Sardinella zunasi (Bleeker, 1854). Both juvenile (chalimus) and adult individuals of this caligid were observed as parasites of the fish host. The discovery suggests that the species has an alternative life cycle as previously proposed for other purportedly ‘planktonic’ congeners and might frequently switch hosts during the adult stage. Thus, the C. undulatus group is newly proposed as a species group in the genus, in which five species are known as planktonic. Some hypotheses on the modified life cycle of caligids also briefly discussed.

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EVALUATION OF MOUNTAIN AREA AS NON-POINT SOURCE OF NITROGEN FOR SETO INLAND SEA: THE NORTHERN SHIKOKU REGION, JAPAN

Proceedings of International Conference "Managinag risks to coastal regions and communities in a changinag world" (EMECS'11 - SeaCoasts XXVI) ◽

10.31519/conferencearticle_5b1b9389d98135.84095825 ◽

2017 ◽

Author(s):

Shohei Morisawa ◽

Yukio Komai ◽

Takao Kunimatsu ◽

...

Keyword(s):

Average Concentration ◽

Point Sources ◽

Seto Inland Sea ◽

Mountain Streams ◽

Unit Load ◽

Mountain Areas ◽

Mountain Area ◽

The Seto Inland Sea ◽

Unit Load Method ◽

Important Position

The northern Shikoku region is located in the Western part of Japan and faces towards the Seto Inland Sea. The forest area, which is one of the non-point sources in the Seto Inland Sea watershed, occupies 75% of the land use in the watershed of the northern Shikoku region. The amount of loadings of nutrients and COD in the Seto Inland Sea has been estimated by the unit load method but actually the data has not been investigated. It is however, necessary to know the real concentration of nitrogen in mountain streams to evaluate the role which is the mountain area plays as non-point sources. Therefore, more water samples of mountain streams in the watershed need to be taken and the concentrations of nitrogen analyzed. The mountain streams in the northern Shikoku area were investigated from April, 2015 to November, 2015. The number of sampling sites was 283, in addition to the past data by Kunimatsu et al. The average concentration of nitrate nitrogen in Ehime, Kagawa, and Tokushima was 0.61mg/L, 0.78mg/L and 0.34mg/L, respectively. The environmental standard range for nitrogen in the Seto Inland Sea is from between less than 0.2mg/L and less than 1mg/L. Therefore, the average concentration of nitrogen in these regions was over category II, and those of mountain streams in Kagawa Prefecture exceeded category III. About 20% of mountain streams were more than 1mg/L. It has become clear that mountain areas occupy an important position as non-point sources for the Seto Inland Sea.

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