Responses of the brackish-water amphipod Gammarus duebeni (Crustacea) to saline sewage
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, more Also appears in:Heip, C.H.R.; Nienhuis, P.H.; Pollen-Lindeboom, P.R. (Ed.) (1992). Proceedings of the 26th European Marine Biology Symposium: Biological effects of disturbances on estuarine and coastal marine environments, 17-21 September 1991, Yerseke, The Netherlands. European Marine Biology Symposia, 26. Netherlands Journal of Sea Research, 30. 299 pp., more |  |
| Abstract | Soon after the opening of the Looe sewage treatment works (Cornwall, southwest England) in 1973, it became colonized by the brackish-water amphipod Gammarus duebeni Liljeborg. The works is unusual as it operates with saline sewage and has a tidally-based pattern of salinity fluctuation (S=13 to 34). Various responses of this unique amphipod population (sewage amphipods) have been compared with G. duebeni from the adjacent Looe River estuary (estuarine amphipods) in an attempt to identify long-term responses to sewage. Sewage amphipods were significantly smaller than their estuarine equivalents; the sewage population was biased significantly to males, whereas the sex ratio of the estuarine population significantly favours females. Compared with the estuary, the consistently lower oxygen levels in the works were reflected in significant differences in metabolism. Sewage amphipods maintained high levels of activity under hypoxia (e.g. swimming), and had higher survival and lower rates of lactic acid accumulation under anoxia than estuarine individuals. In addition, sewage amphipods recovered more rapidly from anoxia and had a lower critical oxygen tension (pc) than estuarine amphipods. Sewage amphipods are exposed to higher levels of heavy metals associated with the domestic sewage and zinc concentrations are particularly elevated in the works. Exposure to elevated zinc concentrations resulted in similar patterns of body zinc uptake for sewage and estuarine Gammarus at high (30) and low (10) salinity, with zinc regulation apparently occurring to an external threshold of 200 µgZn·dm-3. No consistent interpopulational differences in the effect of zinc on zinc uptake or on osmoregulation have been identified. However, sewage amphipods had higher survival at all zinc/salinity combinations compared with estuarine individuals. These findings indicate that sewage amphipods are adapted to the unusual combination of conditions prevailing in the treatment works and, if reproductive isolation is confirmed, suggest that the speciation process may have commenced. |
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