Variability in copepod trophic levels and in feeding selectivity based on stable isotope analysis in Gwangyang Bay off the southern coast of Korea

Abstract

Abstract. Trophism (i.e., food resources and trophic levels) of different copepod groups was assessed along a salinity gradient in the temperate estuarine Gwangyang Bay of Korea, based on seasonal investigation of taxonomic results in 2015 and stable isotope analysis incorporating multiple linear regression models. The Acartia preferred large particles, Paracalanus and Pseudodiaptomus apparently preferred small particles, and Corycaeus was typically omnivorous with low selectivity on particle size. In addition, the carnivorous genus Tortanus predated on copepods without apparent selectivity, Labidocera preferred Acartia to Paracalanus, and Sinocalanus preferred Paracalanus to Acartia and cyclopoids. Overall, our results depict a simple energy flow of the planktonic food web of Gwangyang Bay: 25 from primary producers (nanoplankton) and a mixture of primary producers and herbivores (microplankton), through omnivores (Acartia, Paracalanus, and Corycaeus) and detrivores (Pseudodiaptomus and Euterpina) to carnivores (Tortanus, Labidocera, and Sinocalanus).

Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay

“…Dominant zooplankton had consistent δ 13 C values with those of phytoplankton throughout the year. This result suggests that switching plankton assemblages guarantees the persistence of patterns of planktonic food chains (e.g., trophic base, resource utilization, and trophic niche) 43 .…”

“…Consistently high salinity and low inorganic nutrient concentrations and turbidity in the deep bay reflect that river discharge is rapidly diluted with and diffused into inflowing marine water that is highly dynamic and quickly renewed owing to the short water residence time of 2.5-3.4 d driven by semidiurnal tides 46 . Previous studies also proposed seasonal succession in the phytoplankton community (i.e., relative abundances of centric and pennate diatoms and flagellates) in response to temperature fluctuation, inorganic nutrient loading status and N:P stoichiometry 47 as well as zooplankton assemblages linked to temperature, salinity and Noctiluca vs. diatom densities 43,48 . Our SOM training intuitively differentiated the macrobenthic community into clusters 1 and 2 (estuarine channel) and cluster 3 (deep bay), reflecting a salinity gradient 49 .…”

“…The plankton community was first divided into estuarine-channel and deep-bay clusters. The estuarine-channel clusters were clearly associated not only with the occurrence of freshwater, brackish, and benthic indicator taxa (e.g., Diatom a sp., Nitzchia sp., Cylindrotheca closterium , Sinocalanus tenellus , and T. dextrilobatus ) 43 , 44 but also with low salinity and high inorganic nutrient and chlorophyll a concentrations. Along with the seasonal reduction of river discharge in November and February, the plankton community in the estuarine channel shifted towards deep-bay cluster B.…”