Interactions between native and alien ctenophores: Beroe gracilis and Mnemiopsis leidyi in Gullmarsfjorden
نویسندگان
چکیده
We experimentally quantified predation rates between the native North Sea ctenophore Beroe gracilis and the introduced Mnemiopsis leidyi. A series of incubation experiments with varying M. leidyi prey concentrations (0.15 to 2.37 ind. l–1) and sizes (mean oral-aboral length: 5.9 to 20.6 mm) was conducted, and digestion rates were measured. B. gracilis fed readily on M. leidyi and reproduced on this diet. However, B. gracilis were unable to entirely ingest M. leidyi approaching their own size, resulting in a size refuge from predation. Larger prey were often partially consumed, and the proportion of prey that was only partially eaten increased with prey size. Observed maximum clearance rates for whole prey were from 0.42 to 0.97 l ind.–1 h–1. Ingestion rates of whole prey increased linearly with prey concentration for the smaller prey, but leveled off at the higher prey concentrations for the larger sizes, indicating handling limitation. The handling limitations probably largely stemmed from digestion time (1.6 to 8.4 h for 4 to 12 mm prey) and gut volume. Applying the determined clearance rates to concurrent in situ abundances of M. leidyi and B. gracilis suggested a slight predation impact on the M. leidyi population (overall mortality: 8.8 × 10–4 d–1). The predatory interactions between the 2 species are further complicated by transitional and lobate stage M. leidyi being able to feed on young B. gracilis.
منابع مشابه
Native and non-native ctenophores in the Gulf of Trieste, Northern Adriatic Sea
Observations of ctenophore species were made in the Gulf of Trieste between 2003 and 2006. We examined native ctenophore species with special attention to representatives of the orders Lobata and Beroida, and we recorded among them two non-native ctenophores: Mnemiopsis leidyi A. Agassiz 1865 and Beroe ovata sensu Mayer, 1912. The validity of the Mediterranean species Beroe ovata is discussed. ...
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