This study examined the foraminifera and the ecologic conditions
of the benthic environment of the Oregon shelf and the uppermost slope
(75-550 m depth) between 143°45' N and 144°40' N. Seasonal collections
monitored the near-bottom marine environment and the sedimentary
substrate at 16 stations. The foraminiferal benthic fauna was
examined from eight seasonal stations and two additional stations.
Use of a multiple corer provided randomly selected subsarnples of the
sediment for ecologic and faunal analyses. Use of water bottles that
triggered upon bottom impact provided measurements of the water as
close to the bottom as 0. 6 m. Computerized data processing and
statistical analyses aided the ecologic and faunal evaluations.
The environmental study showed the existence of considerable
variation in the hydrography of near-bottom waters, especially
between summer and winter (upwelling and non-upwelling) collections
at the same station. Upwelling conditions directly affect the benthic
Redacted for Privacy
environment. In addition, the water at any one place, at least dciring
upwelling, was so well mixed that vertical stratification did not exist
between 0.6 and 5.0 m off the bottom. Statistically significant sea-.
sorial variations in surface sediments at the same station were not
observed.
The living benthic foraminiferal fauna exhibited considerable
within-station variation both in species composition and in specimen
size of selected species. The percent abundance of individual dominant
species varied in adjacent cores (subsamples) by amounts up to
46%. Living specimens of a single species were found that were three
times as large as the smallest living specimen from the same sample,
yet there was no evidence of a multimodal size distribution resulting
from age classes.
The author suggests that the dominant species are aggregated
and that the aggregations are colonies of asexually produced siblings.
Lack of fit of species-frequency curves to the lognormal distribution
indicated that relatively few species are fit to reproduce in a particular
environment; most juvenile specimens that enter a particular
environment belong to species that will not thrive there and either die
or simply maintain growth with little chance of reproductive success.
The existence of colonial aggregations of individuals is considered
to provide the best explanation of the observed variations
between adjacent samples. However, the observed variations could be
due to sampling error or to substrate microheterogeneity.
A possible natural community of 15 dominant species has been
determined for those species that form a consistent part of each
other's biologic environment. The community crossed the depth and
substrate boundaries upon which the stations were selected and
appeared to be a general community for the Oregon outer shelf. The
limits of the community appear to be determined mostly by water
depth, with approximate boundaries at 75-100 m and somewhere
between 200-500 m.
Regression analyses to determine the ecologic control on the
foraminiferal fauna did not indicate a close correspondence between
faunal parameters and environmental variables.
Regression analyses to determine the ecologic control on mdividual
species indicated that most species depended upon a set of two
to four environmental variables rather than upon one single limiting
factor. The set for each species was different. Temperature.
phosphate concentration and oxygen concentrations were common hydrographic
members of sets; percent silt, percent sand, percent clay,
organic carbon content and organic nitrogen were common sedimentary
members of sets. / Graduation date: 1972
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29014 |
| Date | 28 October 1971 |
| Creators | Gunther, Fredrick John |
| Contributors | Fowler, Gerald A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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