The classification and structure of marine macrobenthic assemblages at Arthur Harbor, Anvers Island, Antarctica Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5712m8675

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  • In January-February 1971 five replicate 0.07 m² Van Veen grabs were obtained from each of 12 stations in Arthur Harbor and nine Van Veen grabs were obtained from two stations in nearby Bismark Strait. The 69 grab samples yielded 78,395 individuals which were separated into 282 taxa, including 108 species of annelids (54.5% of the individuals), 117 species of arthropods (30.3%), 35 species of molluscs (11.3%) and 22 species in other phyla (4.0%). The density of macrofauna (17,522 individuals/m²) found in Arthur Harbor was high compared to other reported areas. This high density was considered to be the result of high organic input from phytoplankton, phytobenthos and attached macroalgae, the efficient utilization of organic matter by macrobenthos and the slow growth rate of macrobenthic species as an indirect result of cold temperatures. Diversity values were moderately high with high species richness values and low evenness values. The high species richness values may be the consequence of seasonal constancy of temperature and salinity in Arthur Harbor, while low evenness values probably result from the physical stress of iceberg grounding coupled with high organic input. Six macrobenthic assemblages (site groups) and 11 species groups were found in the study area by classification analysis (Bray-Curtis dissimilarity, group-average sorting). Station groups were described by dominant species, density and diversity. Species groups were described by the dominance, fidelity, constancy, and percent abundance of constituent species restricted to site groups. The existence of discrete assemblages derived from the classification analysis was supported by direct ordination. Assemblages were interpreted to be areas of relative homogeneity which interrupt a general continuum of distribution of species with depth. The depth gradient probably represents several factors including increased constancy of temperature and salinity, lower organic input from attached macroalgae and phytobenthos, and a reduced incidence of iceberg grounding. Diversity, species richness, and evenness values increased with the depth gradient, while density values decreased with depth. The dominant species obtained in this study are widely distributed throughout the Antarctic, and 4% of the 162 taxa identified to species were also found at Terre Adelie, East Antarctica. Thus assemblages found in Arthur Harbor are probably circumpolar. In spite of the stability of temperature and salinity, Arthur Harbor macrobenthic assemblages were moderately stressed by glacial activity Icebergs, which often ground in Arthur Harbor, destroyed the benthos by crushing and churning the sediment. The disturbed area was first repopulated by motile, opportunistic species. These species fed on macroalgae which collected in the depression left by the iceberg. Scavengers and carnivores appeared later to feed on the grazers and macrofauna destroyed by iceberg grounding. Within a year the depression filled, and typical meiobenthic assemblages were re-established. Several years may be required before macrobenthic assemblages are re-established. Station 8, located near the glacial face had the lowest values of diversity, species richness, evenness, and density of any station in Arthur Harbor. These low values resulted from physical stress of glacial calving. Large pieces of ice calved from the glacial face and crushed the sediment by impact with the bottom. The waves created by impact of the calved ice with the water also disturbed the sediment creating an unstable sediment surface.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-06-28T20:25:57Z (GMT) No. of bitstreams: 1 RichardsonMichaelD1976.pdf: 1511070 bytes, checksum: fa6cc02bfc7a149d9820c6ab36d10b44 (MD5)
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