Feeding habits and ecological roles of marine cladocerans in offshore zooplankton food-web in Suruga Bay, Japan

Abstract Marine cladocerans, primarily found in shallow coastal waters, play a crucial role in the food-web system. In Suruga Bay, Japan, cladocerans are abundant in offshore waters during the spring–summer season, dominating mesozooplankton communities. However, their roles in offshore food-webs remain unclear. This study focuses on two dominant cladoceran species in Suruga Bay, Penilia avirostris and Pseudevadne tergestina. Both stable isotope ratio and metabarcoding diet analyses were conducted to reveal their feeding habits and trophic positions in offshore food-webs. Stable isotope analysis suggested that the trophic levels of cladocerans are similar to or lower than those of other herbivorous and omnivorous zooplankton. The difference in the δ 15 N values between the two species indicated a lower trophic position for Pe. avirostris than Ps. tergestina . Metabarcoding analysis suggested that while the main prey organisms of the two cladocerans were similar, Pe. avirostris fed on small-sized prey, such as chlorophytes and cyanobacteria, unlike Ps. tergestina . This integrated approach suggests that Pe. avirostris and Ps. tergestina have different feeding habits and trophic positions, playing an important role in connecting lower and higher trophic levels in the offshore food-web.