The Hemigrapsus oregonensis population at Coquille Point in
the Yaquina Bay Estuary on the Central Oregon Coast was studied
from April, 1972 through May, 1973. The population was found to be
vertically stratified from the 1 ft level to the 5 ft level. Population
densities were found to be most dense in the upper regions. Greatest
population density (about 20 crab/m²) was found to be in the 3-4 ft
interval above MLLW (0.0 ft level).
The population sex ratio was biased in favor of the females
(53.3%) and did not vary appreciably during the year. The reproductive
season, as determined by the percentage of berried females,
was from February through May with a peak (32.8%) during March.
Brooding females were found every month during the study, indicating
a continuous, low level egg production throughout the year. A model
for estimating potential egg production is given. The minimum
carapace width of brooding females was found to be 0.86 cm.
Biomass values were determined from carapace width measurements.
A conversion equation is given. Biomass values generally
increased as tidal height increased. The average biomass
value for the area was 8.47 g/m². The average dry weight per
crab decreased as tidal height increased, The average dry weight
per crab at each tidal height (about 0.5 g) did not significantly increase
during the study, suggesting a stable population. The average
monthly production showed an over-all negative rate of -1.23 g/m²
per month. No significant differences were found between tidal
heights. The net production rate at each tidal height could not be
shown to be different from a zero net production rate, again suggesting
a stable population.
Monthly distributional patterns indicated an high degree of
population mobility. Crabs tested for locomotory activity patterns
in the laboratory showed rhythms influenced by both the light regime
and the tidal regime. Weak endogenous displays were found for a
light component with increased activity during dark periods.
Greatest activity generally occurred during dark-high tide periods.
It is suggested that the locomotory activity patterns of H.
oregonensis are influenced by both a tidal cycle and a light cycle.
Under constant experimental conditions, the endogenous
rhythmicity decayed within 3-9 tidal cycles and resulted in more
or less continuous random movements. Only about 50% of the
tested crabs, however, displayed an endogenous locomotory
rhythm. / Graduation date: 1974
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28474 |
| Date | 17 July 1973 |
| Creators | Batie, Robert Edward |
| Contributors | Bayne, Chris |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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