Monitoring of Rhopilema esculentum Resources in Hangzhou Bay in 2024 and Analysis of Bloom Causes

To investigate the spatiotemporal distribution and causes of blooms of Rhopilema esculentum in Hangzhou Bay during 2024, this study investigated its growth characteristics, including umbrella diameter and body weight, along with environmental factors, spatiotemporal dynamics and yield variations. The analysis was based on the 2024 monitoring data of R. esculentum resources in Hangzhou Bay, together with relevant social research data. The results showed that umbrella diameter and body weight increased over time at all monitoring points. The growth rate of the R. esculentum umbrella diameter declined gradually over time, whereas that of body weight rapidly increased. The daily growth rate of umbrella diameter in the water of Tangnao and Xiaoji Mountains was significantly higher than that in the waters of Tanxu Mountain. A sharp drop in salinity caused by Xin’anjiang Reservoir flood discharge from the 23rd to 28th June was the primary cause of the R. esculentum blooms in Hangzhou Bay. During the special R. esculentum fishing period in the summer fishing moratorium, R. esculentum was mainly distributed in the southern and eastern Hangzhou waters, with a maximum daily yield of 28,000 kg/day. After the 16th, R. esculentum production expanded across the entire bay, with blooms also occurring in Xiangshan Bay and Liuheng, reaching a production peak of 44,000 kg/day. In 2024, R. esculentum production in Hangzhou Bay totalled 250,000 tonnes, breaking historical records. This study revealed the 2024 growth and spatiotemporal dynamics of R. esculentum in Hangzhou Bay, providing a reference for the rational use and protection of the species and revealing the causes of the unprecedented blooms.