Abstract:
Plankton samples for this present study were collected from an
area off the southern Oregon coast, extending westward to about 83
kilometers offshore. Over this sampling area, 41 species of adult
copepods were identified, including representatives of 26 genera and
17 families. The total abundance averaged 550/m³.
Population densities of copepods as a group were found higher
inshore than offshore and this distribution was largely determined by
four dominant species, that is, Oithona similis, Pseudocalanus
minutus, Acartia longiremis, and Acartia clausi. They accounted
for approximately 81% of the total copepod abundance.
Species diversity had a tendency to increase with distance
from the coast. This could be due to the possibilities that the
sampling depth was increased offshore, or that the living environment
was more stable offshore than inshore.
Rank-correlation analysis of the four dominant species, fish
eggs, copepod nauplii, euphausiids, and Eucalanus bungii suggest
that the positively correlated category includes several pairs, Oithona
similis to Pseudocalanus minutus, O. sirnilis to Acartia clausi, A.
longiremis to P. minutus, fish eggs to O. similis, A. longiremis to
A. clausi, O. similis to copepod nauplii, and fish eggs to copepod
nauplii. The negatively correlated category includes three pairs,
euphausiids to copepod nauplii, euphausiids to fish eggs, and
euphaus lids to O. similis.
Results from the correlation analysis of the dominant species
relative to temperature, salinity, and distance from shore show that
no significant relationship was apparent except that the occurrence of
P. minutus was negatively correlated to distance from shore.
