|Abstract or Summary
- 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
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
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.