Epifaunal communities thrive in an estuary with hypoxic episodes |
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| Authors: | Alessandra Sagasti Linda C Schaffner J Emmett Duffy |
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| Institution: | 1. School of Marine Science Virginia Institute of Marine Science, The College of William and Mary, 23062-1346, Gloucester Point, Virginia
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| Abstract: | 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 polychaetesPolydora cornuta andSabellaria vulgaris, the bryozoansMembranipora tenuis andConopeum tenuissimum, the tunicateMolgula manhattensis, the barnacleBalanus improvisus, the anemoneDiadumene leucolena, and the hydroidsEctopleura dumortieri andObelia bicuspidata. Common mobile species included the nudibranchsCratena kaoruae andDoridella obscura, the amphipodsMelita nitida andParacaprella tenuis, the polychaeteNereis succinea, and the flatwormStylochus 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 polychaeteS. vulgaris were more abundant in the area with gereally higher oxygen, suggesting that they may be less tolerant of hypoxic stress.
The polychaeteP. 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 lowr 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 O2 I−1) can persist with little change in species composition, and with few changes in abundance, as oxygen concentrations fall. |
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