eDNA-based Ship Tracking Unveils Early Dispersal Patterns and Microecological Dynamics of Ulva prolifera Micropropagules in Yellow Sea Green Tide Outbreaks

Green tides caused by Ulva prolifera in the Southern Yellow Sea pose significant ecological and economic threats. Early detection of micropropagules is critical for effective management. This study systematically investigated the spatiotemporal distribution characteristics and key environmental driving mechanisms of environmental DNA (eDNA) from U. prolifera in early-stage green tide algae accumulation zones in the South Yellow Sea, using eDNA technology combined with environmental parameters. Surveys in April and June 2024 across raft-farming (RD transect) and non-raft (SY transect) areas revealed ecological differences during early green tide development. Key findings include: (1) In April, U. prolifera eDNA abundance in RD showed a "nearshore-high, offshore-low" pattern regulated by temperature and total nitrogen (TN), while SY exhibited similar trends driven primarily by temperature. No significant correlations were observed in June. (2) High U. prolifera eDNA abundance at SY4 in April was driven by hydrodynamics (tidal asymmetry), temperature, and biological interactions (e.g., Cercozoa), identifying a hotspot for monitoring. (3) Raft-farming areas exhibited stronger species interactions, with Chlorophyta and Cercozoa closely linked to U. prolifera. Species such as Ventrifissura sp. STR1224 and Oocystis sp. LN1 show potential as bioindicators for early green tide detection. This is the 18S metabarcoding sequencing data from June.This study provides molecular ecological evidence for multi-source green tide outbreaks, highlights the utility of eDNA in monitoring, and offers theoretical support for marine ecosystem management under climate change.