Opportunistic predation on hydromedusae by the foureye butterflyfish and associated crustaceans

Jellyfish play crucial roles in marine food webs as both predators and prey, but their trophic interactions remain poorly understood due to challenges in systematic observation and sampling. We document opportunistic predation by the foureye butterflyfish Chaetodon capristatus on hydromedusae of the genus Aequorea in Cuba's Cienaga de Zapata Marine Reserve. Two instances of active predation were observed, with butterflyfish selectively consuming portions of the jellyfish bells and subumbrellar regions. Simultaneously, we discovered a prevalent parasitic association between these jellyfish and the hyperiid amphipod Brachyscelus globiceps, with 100% of examined Aequorea (n = 6) hosting between 31 and 67 amphipods each. These observations suggest complex ecological roles for Aequorea in this ecosystem. Supplemental jellyfish consumption could nutritionally subsidize coral reef fish during periods of low prey abundance. However, intense overexploitation could deplete jellyfish populations, potentially disrupting plankton community structure and energy flow through the food web. Conversely, moderate predation on parasitized individuals may facilitate biomass recycling while removing weakened hosts. This study highlights the need for further research to elucidate jellyfish trophic dynamics in the face of environmental change, emphasizing their importance in marine ecosystem functioning and the value of long-term monitoring in marine reserves.