Zooplankton and Neustonic Microplastics in the Surface Layer of Yeosu Coastal Areas

여수 연안 표층에 출현하는 동물플랑크톤과 미세플라스틱

In planktonic ecosystems, the microplastics are considered as a potential food source for the zooplankton. To study a relationship between the zooplankton and the neustonic microplastics, a research experiment was carried out during May in the surface layers of the Yeosu coastal areas including Yeoja Bay, Gamak Bay, Yeosuhae Bay, and Botdol Sea. A neustonic zooplankton net (mesh size $300{\mu}m$; mouth area $30cm{\times}18cm$) was towed from the side of the ship in the event that it would not be affected by waves crashing by the ship at a speed of ca. 2.5 knots. All of the microplastic particles were separated from the zooplankton. The zooplankton and microplastics were appearing in a range of 61 to $763indiv.m^{-3}$ and 0.0047 to $0.3471particle\;m^{-2}$, respectively. It was noted that the Acartia omorii, Paracalanus parvus s. l., Labidocera euchaeta, A. hongi, decapod larvae, and cirriped larvae were predominantly seen in the experiment. For verifying relationships between zooplankton and environmental factors in addition to microplastics, a model redundancy analysis (RDA) was performed. The zooplankton were divided into two groups on the basis of feeding types (i.e. particle feeders, and carnivores), and the associated zooplankton larvae were also separately considered. A review of the additional environmental factors such as water temperature, salinity, turbidity, chlorophyll-${\alpha}$ concentration, diatom density, and dinoflagellate density were also contained in the analysis. The results showed that a noted zooplankton abundance had no close relation with the occurring number of microplastic particles, but rather was significantly related with other noted environmental factors such as temperature, salinity, turbidity, and chlorophyll-${\alpha}$ concentration. This fact implies that most zooplankton can feed themselves as a unit, by selecting the most likely available nutritious foods, rather than microplastics under the circumstance of food-richness areas, such what food resources are available as in the location of coastal waters.

동물플랑크톤과 미세플라스틱과의 상관성을 파악하기 위해 2015년 5월 12일부터 14일까지 여수근해 (여자만, 가막만, 여수해만, 봇돌바다) 총 10개의 정점에서 수표성 동물플랑크톤과 미세플라스틱을 채집하였다. 동물플랑크톤은 요각류 13종을 포함해 총 26개의 분류군이 출현하였고, 그 중 요각류가 가장 높은 비율을 차지하였다. 동물플랑크톤의 출현 개체수는 $61{\sim}763indiv.m^{-3}$, 미세플라스틱은 $0.0047{\sim}0.3471particle\;m^{-2}$의 범위였다. 미세플라스틱은 주로 스트로폼, 페인트 조각, 섬유 조각 등이 발견되었다. Acartia omorii, Paracalanus parvus s. l., Labidocera euchaeta, A. hongi, 십각류 유생, 따개비 유생이 우점적으로 출현하였다. 동물플랑크톤을 먹이식성에 따라 입자식성 동물플랑크톤과 육식성 동물플랑크톤으로 구분하였고, 동물플랑크톤 건조중량도 측정하였으며, 동물플랑크톤 유생은 따로 구분하였다. 이밖에 측정한 환경요인으로는 수온, 염분, 탁도, Chl-${\alpha}$ 농도, 식물플랑크톤 (규조류, 와편모조류) 밀도를 조사하였다. 동물플랑크톤과 미세플라스틱과의 상관성을 분석하기 위해 RDA를 실시한 결과 동물플랑크톤은 미세플라스틱보다 다른 환경요인인 수온, 염분, 탁도, Chl-${\alpha}$ 농도와 밀접한 상관성을 나타냈다. 이는 연안해역과 같이 먹이가 풍부한 해역에서 미세플라스틱이 동물플랑크톤 주요 먹이로서 과대평가되어 있음을 시사할 수 있다.