LONG-TERM ANALYSIS OF POLYCHAETE-DOMINATED BENTHIC INFAUNAL COMMUNITIES IN MASSACHUSETTS BAY, USA
Hilbig, B.1 & Blake, J. A.2
1Zoological Institute and Zoological Museum, University of Hamburg, Martin-Luther-King-Platz, 3, D-20146 Hamburg, Germany
2ENSR, 89 Water Street, Woods Hole, Massachusetts, 02543 USA
The species composition, abundance, and diversity of soft-bottom benthic infaunal communities have been studied as part of a long-term quantitative monitoring program related to the siting, construction, and operation of a sewage outfall in Massachusetts Bay, off Boston. Samples have been collected near and adjacent to the new outfall location as well as at farfield reference locations throughout Massachusetts Bay and Cape Cod Bay. Reconnaissance surveys were conducted in the late 1980's; long-term monitoring began in 1992. The outfall becomes operational in November 1998. Most of the area near the outfall is a naturally disturbed habitat influenced by tidal currents, stormgenerated wave action, and sediment resuspension. Areas of fine to coarse sediment alternate with exposed drumlins (glacial rock formations) and boulder fields. The infauna is dominated by polychaetes, especially spionids (Prionospio steenstrupi, Spio limicola, Dipolydora socialis and D. quadrilobata), capitellids (Mediomastus ambiseta), and cirratulids (Tharyx acutus and Monticellina baptisteae) but due to a patchy environment, species composition varies spatially. Syllids and oweniids are locally dominant. Out of 234 species of infaunal invertebrates identified in the 1996 samples, 103 species (44%) were polychaetes. The largest families were the Spionidae (14 species), Maldanidae (11 species), Cirratulidae and Syllidae (10 species each). Dominant species shift in order from year to year probably in response to timing of recruitment. Different faunal assemblages have been identified in the vicinity of the outfall, all determined by sediment grain size: 1) an Exogone-Corophium-oligochaete assemblage found at coarse-sand stations, 2) a widespread fine-sand assemblage dominated by spionids, M. ambiseta, and sometimes Ninoe nigripes. The dominant spionids change in abundance from year to year, but are always characteristic of normal coastal assemblages. P. steenstrupi dominated in 1987-88 and since 1995; S. limicola was the dominant spionid from 1992-1994. At least two Farfield stations in Cape Cod Bay are dominated by cossurids (Cossura longocirrata).