Scyphomedusae (Phylum Cnidaria, Class Scyphozoa) are perceived as a nuisance due to
their sudden outbreaks that negatively affect human activities (particularly tourism and fisheries)
mainly because of their stings. A brief review of the history of scyphozoan blooms in the Mediterranean
and updated information available after 2010 point to an increase in scyphozoan outbreaks.
Whilst the negative effects on public health, aquaculture, coastal industrial activities and fisheries operations
are undeniable, the effects on the ecosystem are not well defined. We focus on the trophic interactions
between scyphomedusae and fish, highlighting that the negative effects of scyphomedusae
on fish stocks exerted through direct predation on early life stages of fish and competition for plankton are at present
speculative. In favor of a positive effect of scyphomedusae on fish populations, the reports of predation upon scyphozoans
are increasing, which suggests that predators may benefit from the availability of scyphozoans by shifting their diet toward
jelly prey. Additionally, scyphomedusae may provide nursery habitats to early life stages of ecologically and economically
important forage fishes and other organisms which shelter underneath their bells. Together with these
ecosystem services, compounds extracted from scyphozoan tissues and venoms are having a variety of biomedical
applications and are likely to contribute to treat a growing number of diseases, including cancer. Our analysis highlights
that a re-evaluation of the balance between "positive" and "negative" effects of scyphomedusae on the ecosystem and
human activities is needed and provides indications on potential directions for future studies.
Keywords: Blooms, competition, fisheries, jellyfish, predation, therapeutic applications, trophic interactions.
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