Abstract. 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 δ13C and δ15N 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 δ13C values. Calanoid isotopic values indicated a mixture
of different genera including species with high δ15N values (e.g.,
Labidocera, Sinocalanus, and Tortanus), moderate
values (Calanus sinicus, Centropages, Paracalanus,
and Acartia), and relatively low δ15N values
(Eurytemora pacifica and Pseudodiaptomus). 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 < 20 µm vs. microplankton at
20–200 µm) indicated that Acartia and
Centropages preferred large particles; Paracalanus,
Calanus, Eurytemora, and Pseudodiaptomus
apparently preferred small particles. Tortanus was typically
carnivorous with low selectivity on different copepods. Labidocera
preferred marine calanoids Acartia, Centropages, and
harpacticoids; on the other hand, Sinocalanus and Corycaeus
preferred brackish calanoids Paracalanus and
Pseudodiaptomus. 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 (Acartia, Calanus,
Centropages, and Paracalanus) and
detritivores
(Pseudodiaptomus, Eurytemora, and harpacticoids)
to carnivores (Corycaeus, Tortanus, Labidocera,
and Sinocalanus).
Morphology and stable isotope analysis demonstrate different structuring of bat communities in rainforest and savannah habitats