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

• Main Authors: M. Chen, D. Kim, H. Liu, C.-K. Kang
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-04-01
• Series: Biogeosciences
• Online Access: https://www.biogeosciences.net/15/2055/2018/bg-15-2055-2018.pdf

Trophic preference (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 <i>δ</i>¹³C and <i>δ</i>¹⁵N values of copepods in the bay displayed significant spatial heterogeneity as well as seasonal variations, which were indicated by their significant relationships with salinity and temperature, respectively. Both spatial and temporal variations reflected those in isotopic values of food sources. The major calanoid groups (marine calanoids and brackish water calanoids) had a mean trophic level of 2.2 relative to nanoplankton as the basal food source, similar to the bulk copepod assemblage; however, they had dissimilar food sources based on the different <i>δ</i>¹³C values. Calanoid isotopic values indicated a mixture of different genera including species with high <i>δ</i>¹⁵N values (e.g., <i>Labidocera</i>, <i>Sinocalanus</i>, and <i>Tortanus</i>), moderate values (<i>Calanus sinicus</i>, <i>Centropages</i>, <i>Paracalanus</i>, and <i>Acartia</i>), and relatively low <i>δ</i>¹⁵N values (<i>Eurytemora pacifica</i> and<i> Pseudodiaptomus</i>). Feeding preferences of different copepods probably explain these seasonal and spatial patterns of the community trophic niche. Bayesian mixing model calculations based on source materials of two size fractions of particulate organic matter (nanoplankton at  &lt;  20 µm vs. microplankton at 20–200 µm) indicated that <i>Acartia</i> and <i>Centropages</i> preferred large particles; <i>Paracalanus</i>, <i>Calanus</i>, <i>Eurytemora</i>, and <i>Pseudodiaptomus</i> apparently preferred small particles. <i>Tortanus</i> was typically carnivorous with low selectivity on different copepods. <i>Labidocera</i> preferred marine calanoids <i>Acartia</i>, <i>Centropages</i>, and harpacticoids; on the other hand, <i>Sinocalanus</i> and <i>Corycaeus</i> preferred brackish calanoids <i>Paracalanus</i> and <i>Pseudodiaptomus</i>. Overall, our results depict a simple energy flow of the planktonic food web of Gwangyang Bay: from primary producers (nanoplankton) and a mixture of primary producers and herbivores (microplankton) through omnivores (<i>Acartia</i>, <i>Calanus</i>, <i>Centropages</i>, and <i>Paracalanus</i>) and detritivores (<i>Pseudodiaptomus</i>, <i>Eurytemora</i>, and <i>harpacticoids</i>) to carnivores (<i>Corycaeus</i>, <i>Tortanus</i>, <i>Labidocera</i>, and <i>Sinocalanus</i>).