Blooms of Pelagia noctiluca jellyfish appear to be increasing in the Mediterranean Sea and cause economic damage to aquaculture and tourism industries. This species also is known as a predator of fish larvae. We combined data from experimentally measured digestion rates, in situ jellyfish gut contents, jellyfish and fish larva abundances, and temperature to calculate the potential predation effects on fish larvae. Although fish larvae averaged < 1% of the available mesozooplankton at shelf, front, and oceanic stations, they ranged from 5 to 32% of the prey in P. noctiluca. Between 0.3 and 5.5% of the P. noctiluca contained fish larvae. Larvae of myctophids and anchovy (Engraulis encrasicolus) were the most frequently consumed. Digestion times (20 to 500 min) were significantly related to temperature (21-24ºC), but not to larval size (1.5 to 30 mm in length). Jellyfish size (4 to 60 mm in bell diameter) was not tested because small larvae were fed to ephyrae and large larvae to medusae. Digestion times averaged 2.5 h, with a mean possible measurement error of 0.5 h. P. noctiluca densities ranged from 0.5 to 5.0 medusae m-3, with highest densities at the front stations. Fish larva densities ranged from 0.1 to 1.0 larvae m-3, with highest densities at the shelf stations. We estimated that between 18 and 32% of the available fish larvae were consumed daily by P. noctiluca. Thus, P. noctiluca poses an important threat to fish populations and fisheries in the Mediterranean Sea

PICES-2012: Effects of natural and anthropogenic stressors in the North Pacific ecosystems: Scientific challenges and possible solutions, 12-21 October 2012, Hiroshima, Japan

Peer Reviewed