Observations of coastal eutrophication and the succession of hab species in Korean waters over three decades

Kim, Hak-Gyoon, Sam-Geun Lee, Chang-Su Jeong
Marine Environment, Oceanography and Harmful Algal Blooms Research Department, National Fisheries Research & Development Institute
Busan, 619 - 900
Republic of Korea

Email: hgkim@haema.nfrda.re.kr

The concentration of dissolved inorganic nitrogen and phosphate in korean coastal waters has increased over the last three decades. The N/P ratio shows no significant inter-annual change with the exception of the abnormal surplus of nitrogen and phosphate in some waters. Until the 1970s, the outbreaks of harmful algal blooms (HABs) were rare and sporadic, but the frequency and persistence increased during the 1980s. During the last decade, HABs became widespread encompassing the whole coast and persisting more than one month. The gradual coastal eutrophication is consistent with widespread and persistent HABs.

The prevailing species in HABs were diatoms until the 1970s, but the dinoflagellates have been responsible for most of the monospecific and persistent HABs since 1981. In the last decade, the dominant dinoflagellates were Heterosigma akashiwo, Prorocentrum mican, Noctiluca scintillance, and Cochlodinium polykridkoides. Among them, C. polykrikoides has made the most widespread and persistent blooms, extending along the whole southern and eastern coast of Korea. This high density of monospecific Cochlodinium blooms has caused consecutive fisheries damages since 1995. According to the coastal HABs monitoring, spring diatom blooms dominated by Skeletonema costatum are replaced by Heterosigma akashiwo and then Prorocentrum spp. Following these, C. polykrikoides is responsible for the summer harmful dinoflagellate bloom. Skeletonema costatum and Thalassiosira spp. gradually become predominant in fall, and transition into the winter community is completed.

It is clarified that the development of coastal eutrophication leads to frequent, widespread and persistent dinoflagellate blooms, and causes species succession towards high growth and motile species.