Prey Preference of the Freshwater Jellyfish Craspedacusta sowerbii: Integrated Behavioral Observations and Transcriptomic Responses to Phytoplankton and Zooplankton

Freshwater ecosystems are highly vulnerable to biological invasions. The globally distributed invasive hydrozoan Craspedacusta sowerbii imposes strong top-down pressure on plankton communities owing to its distinct feeding selectivity. While prior studies have confirmed its preferential predation on zooplankton over phytoplankton, the integrated mechanisms underlying this prey discrimination remain poorly understood. Here, we integrated behavioral observations and comparative transcriptomics to investigate the prey preference strategy of adult C. sowerbii medusae. Behavioral assays demonstrated active predation exclusively on zooplankton, with no targeted hunting toward phytoplankton. Microscopic observations revealed efficient degradation of ingested zooplankton within 6 h, whereas phytoplankton cells were excreted with no apparent digestion. Transcriptomic analyses indicated that zooplankton feeding induces profound transcriptional reprogramming in C. sowerbii. Genes related to catalytic and hydrolase activities were significantly enriched, accompanied by substantial up-regulation of ribosome biogenesis and mitochondrial oxidative phosphorylation. In contrast, phytoplankton exposure triggered negligible metabolic perturbation. The coordinated activation of hydrolase, protein synthesis, energy metabolism, cytoskeletal movement, and mucus production forms the potential physiological basis for the feeding preference of C. sowerbii. Field observations further suggest that algicidal bacteria in the gastric cavity of medusae may assist auxiliary phytoplankton utilization. This study elucidates the regulatory mechanisms governing the trophic selectivity of C. sowerbii, fills key knowledge gaps in its feeding ecology, and offers new insights into the environmental adaptability and survival strategies of this species.