Jellyfish blooms restructure plankton dynamics and trophic linkages in coastal waters

Jellyfish blooms are increasing globally in frequency and intensity,
introducing complex ecological interactions, yet the mechanisms by which
they alter ecosystem structure remain poorly characterized due to a lack
of sustained field observations. We conducted targeted time-series
observations in Jiaozhou Bay—a representative coastal ecosystem
experiencing Aurelia coerulea blooms—tracking temporal responses of
plankton communities and trophic interactions to jellyfish population
fluctuations. A total of 36 surveys were conducted over three years from
2021 to 2023, yielding comprehensive datasets on biological variables
(jellyfish biomass, zooplankton abundance and composition, phytoplankton
abundance and composition), environmental factors (temperature, salinity,
pH), and nutrient concentrations in the study area. Additionally, we
obtained datasets on the gastric content composition of field-collected A.
coerulea through stomach dissection analysis. We further quantified the
dual roles of jellyfish as top-down predators and bottom-up nutrient
regenerators, linking bloom dynamics to changes in plankton structure and
biogeochemical cycling. Our results revealed that during periods of high
A. coerulea aggregation, the structure of the plankton community changed
markedly, characterized by a sharp decline in zooplankton coupled with the
proliferation of phytoplankton. This top-down feeding effect triggered
potential cascading impacts, decoupling trophic pathways by weakening
zooplankton-mediated energy transfer and releasing phytoplankton from
grazing pressure. Concurrently, jellyfish contributed to biogeochemical
processes by releasing bioavailable ammonium and phosphate, with phosphate
regeneration playing a particularly critical role in stimulating primary
production.