Molecular and Morphological Analyses of the Ichthyoplankton Community in Yueqing Bay, China, Reveal High Species Diversity and Variation in Fish Spawning Activity

Yueqing Bay in China supports important marine resources that sustain local fisheries and food security, but increasing anthropogenic pressures and natural environmental changes threaten its biodiversity. This study used morphological identification, COI DNA barcoding, and 12S DNA metabarcoding to assess ichthyoplankton composition and fish spawning patterns. A total of 13,415 eggs and 17,291 larvae were collected using horizontal and vertical plankton nets. Morphological analysis identified 58 taxa, while molecular methods detected 21 species (COI) and 48 species (12S), with an overall total of 105 species from 78 genera and 42 families. Spawning activity showed clear seasonal and spatial patterns, with the highest abundance and diversity in spring and summer, particularly around Ximen Island and the Bay mouth. These areas function as key spawning and nursery grounds. 12S DNA metabarcoding contributed strongly to species detection, especially for cryptic and morphologically indistinguishable larvae, complementing traditional surveys. The findings provide essential baseline information for monitoring fish stocks, protecting critical habitats, and improving fishery management strategies under increasing anthropogenic and climate-related pressures in Yueqing Bay.