Fig 1.
(A) Schematic map of the Southern Sea of Korea with offshore sampling locations and (B) two intertidal and two subtidal sampling sites in the Yeoja Bay.
Black squares (A) and rectangles (B) represent offshore and subtidal (T1 and T2) trawling sites, respectively; black circles (B) indicate intertidal sites (I1 and I2) where fence nets were deployed. The common reed Phragmites australis was collected at Site P. The ark shell Scapharca subcrenata and the Pacific oyster Crassostrea gigas were cultured by local fishermen and collected at sites S and O, respectively.
Fig 2.
Mean of δ13C and δ15N values (±1 SD) of suspended particulate organic matter (POM), sedimentary organic matter (SOM), microphytobenthos (MPB), and the common reed Phragmites australis.
Black, gray, and white colors for POM and SOM represent the within-bay (Site S), the outer-bay (Site O), and offshore sites, respectively. FPOM, fine POM fraction <20 μm; CPOM, coarse POM fraction of 20 to 180 μm.
Fig 3.
Seasonal variations in (A) δ13C and (B) δ15N values of Scapharca subcrenata, and (C) δ13C and (D) δ15N of Crassostrea gigas.
Mean represents annual means (±1 SD). Circles represent the bivalves; triangles coarse (gray) and fine (black) particulate organic matter (CPOM and FPOM), respectively.
Fig 4.
Dual plots of mean δ13C and δ15N values for food sources (black color) and consumers in spring (white) and fall (gray) in (A) intertidal, (B) subtidal, and (C) offshore habitats.
Vertical and horizontal bars represent standard deviations. FPOM, fine (< 20 μm) suspended particulate organic matter; CPOM, coarse (> 20 μm) suspended particulate organic matter; SOM, sedimentary organic matter; MPB, microphytobenthos; Phragmites, Phragmites australis; Riverine POM, Riverine particulate organic matter [57]. MPB, Phragmites, and Riverine POM are in grey on B and C plots because they were not sampled at the subtidal and offshore areas. Dashed lines indicate the average trophic enrichment factors of +1.7‰ and +1.7‰ for δ13C and δ15N values in the ark shells; +1.8‰ and +2.8‰, respectively, in the oysters obtained in the present study.
Fig 5.
Scatter plots comparing (A) δ13C and (B) δ15N of consumers collected in both spring and fall in intertidal, subtidal, and offshore habitats.
Values are mean δ13C and δ15N (‰ ± 1 SD). The dashed lines represent the 1:1 ratio line.
Fig 6.
Frequency distribution of individual consumer δ13C (‰) collected in (A) intertidal, (B) subtidal, and (C) offshore habitats.
Gray bar segments represent motile consumers and black bar segments sedentary consumers.
Table 1.
List of intertidal and subtidal consumers whose isotope composition was analyzed in the present study.
Fig 7.
Dual plots of mean δ13C and δ15N values for sedentary and motile invertebrates, and fish in spring (white) and fall (gray) in (A−C) intertidal and (D−F) subtidal habitats.
The groups of taxa were clustered according to the result of hierarchical cluster analysis (see details in Methods). Numbers designate different taxa (see Table 1 for species code). Circle, suspension feeder; triangle, deposit feeder; diamond, omnivore; inverted triangle, carnivore and scavenger; square, fish. Grey ellipses represent potential sources of organic matter: SPOM, suspended particulate organic matter; SOM, sedimentary organic matter; MPB, microphytobenthos.
Fig 8.
Dual plots of mean δ13C and δ15N values for zooplankton, other invertebrates, and fish in spring (white) and fall (gray) in offshore habitats.
The groups of taxa were clustered according to the result of hierarchical cluster analysis (see details in Methods). Circle, zooplankton; triangle, arthropods; diamond, mollusks; square, fish. Grey ellipses represent suspended particulate organic matter (SPOM) and sedimentary organic matter (SOM). Species name and isotope data are given in S1 Appendix.
Table 2.
The 95% credibility intervals of trophic contribution (%) of organic matter sources or prey groups to the diet of the consumer groups.