|Abstract or Summary
- The foraminiferal population of Yaquina Bay was investigated
to attempt a correlation of seasonal changes in the hydrography with
observed changes in the faunal distribution patterns. The results
are based on data from two spatial surveys conducted in July 1966,
and late February and March, 1967.
The hydrography of Yaquina Bay undergoes seasonal changes
closely paralleling the seasonal precipitation pattern. Except for
short-term variations, the estuarine system is partly-mixed during
the period of maximum river discharge (November to May) and wellmixed
from June through October. Coastal upwelling (high salinity,
low temperature) has a marked influence on the hydrography of the
lower bay during the summer; maximum salinities and temperatures
prevail in the upper reaches of the estuary during late summer and
Species associations were determined by the Fager-McConnaughey
correlation coefficient method; similar assemblages were
found for both summer and winter surveys. A marine biofacies
fauna, dominated by Elphidium microgranulosum and E. frigidum,
occupies the main estuary channel for about five miles upstream.
The distributional patterns of the living fauna show evidence of a
stronger marine influence during the summer, corresponding to
a similar pattern in the hydrography.
In the lower bay, the Elphidium fauna is displaced laterally
by an assemblage characterized by Trochammina charlottensis and
Elphidium incertum in the middle intertidal zone. This assemblages
in turn gives way to an Ammobaculites exiguus -Miliammina fusca
fauna in the upper intertidal area. The Elphidium assemblage gives
way to a Miliammina fauna in the upstream direction. Trochammina
inflata, T. macrescens, Miliammina fusca, Jadamminina polystoma,
Haplophragmoides sp., H. hancocki and Siphotrochammina lobata
are the principal species found in the marine marsh.
Zones of environmental similarity were defined by the index
of affinity association analysis. Living and total faunas of both winter
and summer surveys were considered separately; several sample
groups were defined in each case. Index of affinity data can also
be used to provide an index of the marine influence on the foraminiferal
population of the estuary.
Species diversity or the average number of species/sample,
ranges from 22 in the marine biofacies zone to six on the lower bay
tideflats. An intermediate value (l0/sample)was found for the
Highest standing crops were found in the marshes (summer)
and on the tideflats adjacent to the lower bay channel, averaging 40
and 42/cm² respectively. Lowest values (1 to 2 cm²) were found
in the middle to upper intertidal areas of the lower bay during the
summer. The distribution of the total fauna is quite similar to that
of the living population. Highest average values (175/cm³) are again
found in the marine marsh and in the marine biofacies zone (70 to
80/cm³). Lowest values occur on the lower bay intertidal areas
(3 to 9/cm³).
In general, the percentage representation of agglutinated species
in the total fauna increases with distance upstream in the channel
and with distance laterally from the channel axis. Faunas of some
marsh stations are composed entirely of agglutinated species. The
percentage of calcareous hyaline species shows an inverse relation
to that of the agglutinated fauna, increasing in importance with
approach to marine conditions. Porcelaneous and planktonic species
are generally minor constituents in the total fauna and are
restricted to the marine biofacies as it is developed in the estuary.
Foraminifer-ostracod ratios are extremely variable in the
environments sampled in Yaquina Bay. Smooth-valved species are
characteristic of the marine marsh and inner bay environments;
valve ornamentation tends to increase with approach to marine conditions.
Thecamoebians are present in low numbers throughout the
estuary. In general however, the number of species and population
size increases in the upstream direction.