The microdistribution of the amphipod Eohaustorius brevicuspis was
examined over a 19 month period. Field sampling was conducted principally
at Lost Creek State Park, Oregon, and on one occasion at Driftwood State
Park, Oregon. Both are high-energy, fine sand beaches which appear to be
uniform. Stratified random samples were taken with each of a series of
corers of varying diameters. For the samples obtained for each size of
corer, indices of dispersion were calculated and evaluated to obtain information
on the size of patches, the distribution of individuals within patches,
and the distribution of the patches. E. brevicuspis from Lost Creek at
natural densities were placed in a box of thoroughly sieved, well-mixed
sand in the laboratory, together with natural densities of other macrofauna,
or with other macrofauna excluded. The positions of individuals in the
box were determined by partitioning the Sand into 192 blocks (2 cm by 2 cm)
horizontally, and into 3 layers (6.6 cm deep) vertically. In two of five
experiments, the length and sex of every individual were also recorded
Additional experiments were conducted to examine the predation rate of the
isopod Cirolana harfordi on E. brevicuspis, to test for endogenous tidal
periodicity in the depth in the sand at which E. brevicuspis is found,
and to determine the direction of burrowing during downward migration.
Patches of higher density were variable in size, but occurred most
frequently with diameters near 15 cm. In the field, larger-scale patches
with diameters of two meters were also found In laboratory experiments,
the number of individuals per patch and the number of patches varied with
the overall density. Patches were surrounded by low-density areas containing
from 1/4 to 1/10 as many individuals per unit area. Individuals within
patches tended to be spaced uniformly. It was not possible to determine the
distribution of patches. Patches were formed in the laboratory in the
absence of predators, other macrofauna, and observable environmental
heterogeneity. They appear to be present at all times, although downward
migration at low tide and upward migration at high tide was indicated.
Over six hours, an artifically created patch of dyed amphipods migrated
downward but did not spread horizontally, suggesting that individual
patches could remain intact through one or more tidal cycles. There was
no segregation of different sexes or sizes into different patches, although
smaller individuals tended to be located nearer the surface of the sand.
Patchiness is this species is probably not caused by responses to physical
environmental heterogeneity, or to other macrofauna (including both
predators and competitors), nor by behavior associated with reproduction.
Some possible consequences of the observed distribution of this species
were discussed. / Graduation date: 1979
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27806 |
| Date | 13 April 1979 |
| Creators | Kemp, P. F. |
| Contributors | Gonor, J. J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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