새만금 방조제 해역 중형동물플랑크톤의 군집 특성

Abstract

This study investigates the spatiotemporal variation of environmental factors and mesozooplankton community in the Saemangeum Dyke area, an artificial coastal system affected by the construction of a large-scale dyke from 2012 to 2014. Environmental factors and mesozooplankton were investigated at eight stations of the Saemangeum Dyke area from 2012 to 2014: five in the inner region and three in the outer region.

Water temperature ranged from 3.7–25.6 ℃ in the inner region of the Saemangeum Dyke and 4.6–27.7 ℃ in the outer region of the Dyke. Salinity remained relatively stable at an average of 30 psu or higher in the outer region of the Saemangeum Dyke, while it varied significantly between 9.8–29.8 psu in the inner region of the Dyke. Dissolved oxygen (DO) concentrations were observed at 3.8–13.6 mg/L and 4.0–12.7 mg/L in the inner and outer regions of the Saemangeum Dyke, respectively. Chlorophyll-a (Chl-a) concentrations displayed broader variability in the inner region of the Saemangeum Dyke (1.4–178.8 ㎍/L) compared to the outer region of the Dyke (0.1–16.6 ㎍/L).

Throughout the study period, a total of 84 mesozooplankton taxa or subgroups were identified, with 69 taxa recorded in the inner region of the Saemangeum Dyke and 73 in the outer region of the Dyke. Mesozooplankton abundance varied from 98.8–46,547.4 inds./m³ in the inner region of the Saemangeum Dyke and 249.0–5,387.3 inds./m³ in the outer region of the Dyke, with more significant temporal variability observed in the inner region of the Dyke. In the inner region of the Saemangeum Dyke, mesozooplankton abundance was positively correlated with surface Chl-a concentrations. In contrast, in the outer region of the Saemangeum Dyke, mesozooplankton abundance exhibited negative correlations with surface, bottom, and average salinity.

From 2012 to 2022, water temperature in the Saemangeum Dyke area increased while salinity and DO levels progressively declined. Chl-a concentrations generally increased but demonstrated significant interannual and seasonal variability. The number of mesozooplankton taxa decreased, with copepod species peaking in 2017 before declining. Mesozooplankton abundance sharply increased in 2014, followed by a gradual reduction. Mesozooplankton diversity indices varied highly due to environmental changes and dominance of specific taxa, with a general decline from 2012 to 2020 and partial recovery after 2021.

Throughout most sampling periods, 100 ㎛ and 200 ㎛ nets yielded similar results for total taxa, copepod species, copepod nauplii, copepod abundance, cirriped abundance, cladoceran abundance, and community diversity indices. However, the 300 ㎛ net consistently produced significantly lower results. Total mesozooplankton abundance and copepod nauplii abundance differed between the 100 ㎛ and 200 ㎛ nets, with smaller mesh sizes capturing more organisms. These differences likely stemmed from the inability of the 200 ㎛ and 300 ㎛ nets to collect smaller nauplii and microzooplankton. The cladoceran abundance was less affected by mesh size, suggesting lower susceptibility to mesh size ranges. Mesozooplankton community structure differed significantly by mesh size, with the 300 ㎛ net showing distinct community compositions compared to the 100 ㎛ and 200 ㎛ nets.

This study highlights the ecological impacts of large-scale coastal constructions on marine environments and mesozooplankton communities. This underscores the importance of selecting appropriate sampling gears and the necessity of long-term monitoring to provide critical scientific insights for marine ecosystem conservation and restoration strategies.