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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Epifaunal communities thrive in an estuary with hypoxic episodes
Auteurs :	A. Sagasti, Auteur ; L. C. Schaffner, Auteur ; J. E. Duffy, Auteur
Type de document :	Article
Dans :	Estuaries (23(4) AUG 2000)
Article en page(s) :	474-487
Résumé :	We characterized the abundance and species composition of sessile and mobile epifaunal assemblages in the York River, a tributary of the Chesapeake Bay, U.S., during the summer hypoxia seasons in 1996 and 1997. We collected communities on artificial substrates in two areas of the river that have historically experienced different exposure to hypoxia. Despite frequent hypoxic stress, epifauna formed dense communities in both areas. Dominant species comprised a range of phyla and included the polychaetes Polydora cornuta and Sabellaria vulgaris, the bryozoans Membranipora tenuis and Conopeum tenuissimum, the tunicate Molgula manhattensis, the barnacle Balanus improvisus, the anemone Diadumene leucolena, and the hydroids Ectopleura dumortieri and Obelia bicuspidata. Common mobile species included the nudibranchs Cratena kaoruae and Doridella obscura, the amphipods Melita nitida and Paracaprella tenuis, the polychaete Nereis succinea, and the flatworm Stylochus ellipticus. We found few differences in species composition between the two areas;, even though one area usually experienced lower oxygen concentrations during hypoxic events, suggesting that hypoxia does not exclude any epifaunal species in the York River. We did find differences between the two study areas in percent cover and abundance of some species. While tunicates, hydroids, and anemones were equally abundant in both areas during both study years, bryozoans and the polychaete S. vulgaris were more abundant in the area with generally higher oxygen, suggesting that they may be less tolerant of hypoxic stress. The polychaete P. cornuta was more abundant in the area that usually had lower oxygen. These results suggest that many epifaunal species have high hypoxia tolerance, and most epifaunal species found in the lower York River are able to survive in hypoxic areas. Epifaunal species are not necessarily more susceptible to hypoxia than infaunal species in the York River. Epifaunal communities in areas with brief hypoxic episodes and moderate hypoxia (0.5-2 mg O(2) l(-1)) can persist with Little change in species composition, and with few changes in abundance, as oxygen concentrations fall.

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