Planktonic cnidarian distribution and feeding of <Emphasis Type="Italic">Pelagia noctiluca</Emphasis> in the NW Mediterranean Sea |
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Authors: | Ana Sabatés Francesc Pagès Dacha Atienza Verónica Fuentes Jennifer E Purcell Josep-María Gili |
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Institution: | 1.Institut de Ciències del Mar,CSIC,Barcelona,Spain;2.Shannon Point Marine Center,Western Washington University,Anacortes,USA;3.Coastal and Marine Resources Centre,University College Cork,Cobh, Co. Cork,Ireland |
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Abstract: | Pelagic cnidarians are important consumers of zooplankton and ichthyoplankton in the world’s oceans, and thus harm fisheries
as competitors and predators of fish. This study examined the inshore-offshore distribution of pelagic cnidarians and the
trophic ecology of Pelagia noctiluca ephyrae (<12 mm diameter) and larger medusae in late spring 1995 in the NW Mediterranean Sea. The distribution of pelagic
cnidarians was closely related to the presence of the shelf-slope front with most species mainly concentrated close to the
front. Meroplanktonic antho- and leptomedusae predominated in coastal waters and more holoplanktonic trachy- and narcomedusae
occurred both in shelf and open sea waters. P. noctiluca was more abundant than other medusae, including hydromedusae. Siphonophores, particularly Muggiaea atlantica, outnumbered medusae at most stations. The diet of P. noctiluca ephyrae contained mainly copepods, but ~12% of the prey were fish larvae. P. noctiluca exhibited positive prey selection for chaetognaths and mollusc larvae in day and night samples, but fish larvae were positively
selected only at night. These differences may be related to the diel vertical distributions of P. noctiluca and their prey. Most of the ingested fish larvae belonged to the family Myctophidae, but anchovy and sparid larvae also were
found in the gastric pouches. The size of ingested fish larvae increased as ephyra diameter increased; however, in the larger
medusae (>12 mm) the number of prey increased with medusa size rather than the size of the larvae. The temporal and spatial
co-occurrence of P. noctiluca with early life stages of fish suggests that P. noctiluca may be an important predator on summer ichthyoplankton. |
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