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OCEANOGRAPHY
YAQUINA BAY ZOOPLANKTON
SURVEY I
by
SCHOOL OF SCIENCE
OREGON STATE UNIVERSITY
Herbert F. Frolander
M. Joan Flynn
Sharon C. Spring
Steven T. Zimmerman
Charles B. Miller
Data Report 48
Reference 71-21
August 1971
YAQUINA BAY ZOOPLANKTON SURVEY
I
by
Herbert F. Frolander
M. Joan Flynn
Sharon C. Spring
Steven T. Zimmerman
Charles B. Miller
Data Report 48
Reference 71-21
August 1971
John V. Byrne
Chairman
Department of Oceanography
Oregon State University
Corvallis, Oregon
97331
Introduction
In 1960 a program of monitoring the zooplankton populations of Yaquina
Bay, Oregon, was begun. The frequency of sampling was maintained at close
to weekly intervals after 1 January 1963, usually at five stations.
Abundances of all the species found in the bay of both meroplankton and
holoplankton have been estimated in the samples through August of 1970.
Temperature, salinity, and oxygen concentration were measured at the water
surface and near the bottom in conjunction with each sample. This huge body
of data contains information about the seasonal cycles of bay species and
species from the nearby ocean. It permits study of year-to-year variation
of abundance and seasonal cycle over 71years, and it aids the study of
distributional patterns in the bay.
This report is a first presentation in graphical form of data from stations at navigational buoys 15 and 21 (Fig. 1), together with a listing of
the most evident conclusions. These stations were chosen for earliest consideration because the time sequence of samples is far more complete than at
the other stations since they are closest to the boat mooring. Only the
dominant, holoplanktonic forms are considered in the present report. These
are all copepods or cladocerans.
A study of the bathymetry, drainage area, tidal prism and tidal currents in Yaquina Bay has been provided by Goodwin, Emmett, and Glenne (1970).
Station 15 is in the large embayment that starts 3.2 km from the mouth of
the bay. This bay largely fills and empties on each tide: the tidal prism
at station 15 is 21.4 x 10 6 m 3 , and the cross-sectional area of the bay at
124°06 W.
NEWPORT
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;
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BRIDGE
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Fig
44°
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AVY
-,
,:
2*
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-21
c9 y
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ki.
KILOMETERS
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------i
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----"..."
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91 2___
CONTOUR INTERVAL 12 FEET
DATUM MEAN LOWER LOW WATER
•
Contours compiled from U. S.
C. & G.S. 1953 smooth sheet
124 °00'W.
Fig.
1. Map of Yaquina Bay showing station locations.
-45
3
mean lower low water is only 28% of that at mean higher high water. Therefore,
the planktology of station 15 is probably much like that of the nearby neritic
zone. Station 21 is in the Yaquina River just upstream of the bay proper.
Its tidal prism is smaller, 13.3 x 10 6 m 3 , and its planktology is likely to be
more affected by differences between the river upstream and the neritic zone
offshore than is station 15.
The densities of the planktonic populations in the bay vary spatially
parallel to the upstream-downstream gradients in physical factors (Frolander,
1964). Figure 2 shows the results from a sequence of samples taken from a
station 10 miles offshore (NH 10) to a station at navigational buoy
39 in
Yaquina Bay. These distributions are believed to be typical for mean higher
high water. They are shifted upstream and downstream by flood and ebb
tides respectively (Frolander,
1964).
Acartia longiremis (Lillieborg, 1853)
is most abundant at NH 10 and farther offshore, but it is found inside
Yaquina Bay. Acartia clausi (Giesbrecht, 1889) is most abundant very close
to the coast and abundant in the lower reaches of the estuary. There is
some evidence from size frequency distributions and coloration that there
are two species or ecophenotypes sharing the name Acartia clausi in the bay.
There is a smaller form found typically at and above station 29 and a
larger form found at station 29 and below. These have not been distinguished
in the routine counts. Acartia tonsa (Dana,
1848) is most abundant upstream
from station (Buoy) 29. There is also evidence that Acartia tonsa has
more than one form in the bay. Pseudocalanus gracilis (Sars, 1903) is
abundant farther to seaward than Acartia clausi, but it reaches its maximum
14
Acadia clausi
Acadia tonsa
Pseudocatanus
graci/is
Acadia
tongiremis
Station Number
Fig. 2. Spatial survey of zooplankton densities at stations in Yaquina Bay
and from the shore to 10 miles at sea (NH 10). Data is for
30 July, 1969 from 1000 to 1500 hr.
5
abundance in the same very nearshore zone and shows that same pattern of
decreasing abundance upstream.
The species above, while present all year, are most prevalent in
spring and summer. Corycaeus anglicus, (Lubbock,
(Claus,
1857) Paracalanus parvus,
1863) Evadne nordmanni, (Loven) and Podon leuckarti, (Sars) reach
their maxima in late summer, fall or winter. Corycaeus anglicus is a
coastal species distributed from the Washington and Oregon coasts on south.
It is carried north along these coasts in winter by the slow northerly
coastal current of that season, the Davidson Current. Paracalanus parvus
is both oceanic and neritic in distribution and is carried north in
abundance by the winter currents. The offshore distributions of Evadne
nordmanni
and Podon leuckarti are not well known.
E. nordmanni is most abundant at station
bay. P. leuckarti
In the bay (Fig.
3)
29, but is found throughout the
was lumped in the counts for many dates with P. poly-
phemoides, (Leuckart) so the two species are combined in all the data
presented in this report. P. leuckarti is the more abundant of the two.
Eurytemorea (americana Williams,
3) in summer.
(Fig.
1906) is most abundant in mid-bay
It is an estuarine species that is apparently never
abundant in the very nearshore zone outside the bay. Oithona similis,
(Claus,
1866) is an almost cosmopolitan form.
It is very abundant in Oregon
neritic waters at times, though the seasonal cycle in the ocean is not yet
known.
Several sources of variability affect the accuracy with which a given
sample represents the density of animals for the week it was taken. Results
of studies of sampling variability are summarized by Wiebe and Holland
(1968).
6
1000
500
Podon
leuclrorti
(7 Sept. /968)
100
50
Eurytemoro
americana
(26 JULY /968)
I0
5
Evodne
nordmonni
( 7 Sept. /968)
0
BUOY 15 BUOY 21 BUOY 29 BUOY 39
Station
Fig. 3. Distributions in Yaquina Bay of Evadne nordmanni, Podon spp., and
Eurytemora americana.
7
For a population of density estimates they show that the mean can be
taken to be 25% to 400% of a given single estimate in 95% of cases. This
source of variability is small in the present study compared to that introduced by the tide. No attempt was made to take the samples at a particular
stage of the tide. They were usually taken between 1000 hr and 1600 hr
without respect to the tide. Combined with the weekly sampling interval,
this frequently resulted in long sequences of samples taken alternately
on high and low tides. The magnitude of the changes in abundance at a
particular station attributable to tidal shifting of the whole upstreamdownstream gradient is indicated in Figure 4. A summary of this and
other sequences of samples over one or more tidal cycles is that the highest
densities observed are likely to be 10 to 30 times the lowest. Except
when very low densities are reached, and ratios become an inappropriate
measure of tidal change, a factor of 30 is probably a sufficiently conservative estimate of the effects of the tide. The seasonal changes to be
discussed below are considerably larger than this seemingly crude level
of resolution.
Methods
Weekly sampling was done from small boats. Plankton samples were
made with a Clarke-Bumpus net (mouth diameter 12.5 cm) with its openingclosing apparatus tied in the open position. Number 6 mesh, 0.239 mm, was
used for all tows reported here. Tows were oblique to a depth of about
meters up to mid-1968 and to depths of 8 to 11 meters afterward. The
quantity of water filtered was estimated with a propellor flow meter in the
mouth of the net. Meters were calibrated approximately annually. Calibra-
8
5000
2000
a)
4ai
1000
.0
500
E
z
200
I00
Higher
High
Water
1 (+774,
-
18
Lower
Low
Water
1 (-0.7)1,
0
Lower
High
Water
1
6
Higher
Low
Water
(+6.6) , 1 (+2.3)1
12
1
18
Time of Day
Fig. 4. The density of Acartia clausi
September, 1971.
at station 21 in Yaquina Bay on 9
9
tion factors for all years were within 20% of the mean of all years. Volumes
filtered were typically 3 to 15 m 3 . Samples were preserved immediately
after the tow with formaldehyde.
Water samples from near the bottom were taken with Nansen or N.1.0.
bottles. Samples from the surface were taken with a bucket. Salinity was
determined by inductive salinometer. Oxygen concentration was estimated
by the Winkler method. Temperatures near the bottom were obtained with
reversing thermometers. Surface temperatures were taken with a bucket
thermometer.
Plankton samples were subsampled with a Stempel pipette following
the method of Frolander (1968).
The sample and its preservative are
diluted to a volume 5 to 10 times the settled volume of the plankton. The
plankton are then stirred and a 1 ml subsample removed with the pipette.
Total counts of the small estuarine and neritic forms are typically 350 to
450 with this method. Counts lower than this range are enlarged by counting
one or more additional subsamples.
The counts, volume filtered, subsample fraction and physical data were
punched on cards for computer analysis. The graphs presented were plotted
on a 30 inch CalComp plotter using control routines developed by Gemperle
and Keeling (1970) for the Oregon State CDC 3300 computer. The graphs of
population density against data of collection are plotted on semi-log scales
because the data can be more economically presented, and because the essentially multiplicative tidal variability is represented by an interval of
constant length at all points on the density axis. Along with population
density, four point running averages of population density are plotted on
1
0
each graph. The running averages for density are calculated for logarithms
to base 10 of the density and in effect are transformed to a four point
running geometric mean before plotting on the semi-log scales. This smooths
some of the widest fluctuations caused by tidal movement of populations
and emphasizes seasonal changes in density.
Results
Acartia clausi (Figs.
5
and 6) is present throughout the year. Typical
winter abundances at station 15 for all categories (females, males and
immatures) are less than 10/m 3 . Mid-summer abundances are 1000 to 10,000/m3.
In most years there is a gradual increase in spring and gradual decrease in
fall with no evidence of a "spring bloom", summer low and "fall bloom".
However, 1963, 1969, and 1970 do have signs of the latter pattern with a
mid-summer low. Apart from this there is no evidence of differences between
years in the density of A. clausi. Abundances of males, females and
immatures are closely correlated; increases and decreases in density occur
in nearly identical patterns in the three categories. This implies that they
have similar spatial distributions in the bay and are affected the same way
by the tides. There is no evident lag in the spring between the increase
of immatures and that of adults. This does not necessarily imply a very
short life cycle time, since only the largest copepodites are retained by
the net.
It is clear, however, that at most a few weeks are spent in the
late copepodite stages.
At station 21 (Fig. 6) A. clausi shows much the same seasonal and
year-to-year patterns as at station 15. There is a tendency for the density
at station 15 to be lower in winter and to stay low longer than at station
Acartia clausi
Z 10,000
o 1000
100
(...)=
■
10
I
:5
Z
1963
I
1964
I
Fig. 5.
1965
I
1966
Density of Acartia clausi
I
1967
1968
at station 15 in Yaquina Bay.
1969
I
1970
hJ
Buoy 21
1963
I
1964
Fig.
I
6.
1965
Acartia clausi
1966
Density of Acartia clausi
I
1967
I
1968
at station 21 in Yaquina Bay.
1969
I
1970
13
21. This was particularly evident in the winters of 1963-64 and 1967-68.
This may be a difference between the smaller upstream form and larger
downstream form in temperature tolerance. No investigation has been made
of this possibility. Station 21 shows to a marked degree the effect of
tidal aliasing, weekly alternation between increasing and decreasing density.
Pseudocalanus gracilis at station 15 (Fig. 7) reaches maximum density
in summer. The seasonal pattern is more pronounced after the winter of
1968 than previously. Also, total density frequently reached 6,000/m3
after the winter of 1967-68 compared to highs of about 2000/m 3 previously.
This may be an effect of the change in sampling depth at that time, or it
may be a real change. A study of the depth distribution of this species in
Yaquina Bay would help to select between these alternatives.
Immature P.
gracilis are more abundant than adult P. gracilis in these samples to Acartia
clausi. This is probably because P. gracilis copepodites are larger than
those of A. clausi at the same stages and are retained at younger ages by
the net. At station 21 (Fig. 8) P. gracilis is consistently less abundant
than at station 15, and the frequency of zero samples is much higher, particularly in the adult categories.
Evadne nordmanni (Figs. 9 and 10) makes its first appearance in late
spring: May or June.
It rapidly reaches densities of 200 to 400/m 3 at
station 21 that are sustained until about November when there is a rapid
drop. Abundance was lower and less sustained through the summer of 1969
and 1970 than in earlier years. The significance of this is not known.
Podon spp. (Figs. 9 and 10) are more restricted to mid-summer and fall than
E. nordmanni. Their usual peak density is a few hundred/m 3 at station 21.
In some years, especially 1964 and 1967, they were caught only on a few
Buoy 15
Pseudocalanus gracilis
immatures
1963
1964
Fig.
I
1965
1966
1967
1968
1969
7. Density of Pseudocalanus gracilis at station 15 in Yaquina Bay.
1970
Buoy 21
10,000
100a
100
ID_
Pseudocalanus gracilis
immatures
1114
1963
•
IlTS
1964
Fig.
8.
,
ti
1965
1966
(‘ 1! ,
I
1967
I
A virA
Iiiir
1969
I
1968
Density of Pseudocalanus gracilis at station 21 in Yaquina Bay.
I
1970
O's
Buoy 15
Podon spp.
ffi
Fig. 9. Density of Podon spp., Evadne nordmanni, and Oithona similis
females at station 15 in Yaquina Bay.
Oithona similis
I
1963
1964
r
A(
1965
females
1966
1967
1968
Fig. 10. Density of Podon spp., Evadne nordmanni, and Oithona similis
females at station 21 in Yaquina Bay.
1969
1970
18
occasions. The frequency of sampling is too low to attach any significance
to these apparent differences between years. E. nordmanni appears to be
more abundant in all years at station 21 than at station 15. Podon spp.
are about equally abundant at the two stations.
Oithona similis (Figs. 9 and 10) is more haphazard in its times of
abundance and rarity than any of the other species considered. There is a
suggestion in the data for 1965 and after, of higher abundances in the spring
and fall than at other times. This species is more abundant at station 15
than at station 21.
Corycaeus anglicus (Figs. 11 and 12) first appears in August or
September and is present until about March. The occasional individual
caught at station 21 in mid-summer in 1968 and 1969 may result from the
deeper sampling of the later years. A few animals probably persist at depth.
Station 15 has consistently higher densities of C. anglicus than station 21,
which implies that influx from the ocean population controls are measured
densities in the bay. No explanation has been found for the low densities of
1964-65.
Paracalanus parvus (Figs. 11 and 12) is generally present at both
stations 15 and 21 after 1 September and persists in the bay until May.
Occasionally a few still are present in mid-summer. Males have a usual
maximum density of 100/m 3 ; females reach 300 to 400/m 3 . There are no
notable differences between years in the density of this species.
Eurytemora americana (Fig. 13) can be found in low numbers at any
season.
It rapidly becomes abundant in early spring and then gradually
declines throughout summer and fall.
Temperatures (Fig. 14) at both stations 15 and 21 are highest in
Buoy 15
10,00_0.
Paracalanus• parvus
100n_
tr
100
females
4`ol
■\
tQ
"
11 0
-7-5
\01
v-1
IN
10,000
1000
100
10
males
/ \id!
i)
-1 0
z
10,000
A
„i/ m1
PI
°11
Corycaeus anglicus
1000
total mature
100
I
,A
10
'
ME
IA
1963
1964
I
1965
4
k
Li
1966
1967
/nal
t
1968
Fig. 11. Density of Paracalanus parvus and Corycaeus anglicus at station
15 in Yaquina Bay.
1969
j I
I
1970
Buoy 21
10,000
Paracalanus parvus
Corycaeus anglicus
1000
total matures
100
10
1963
1964
1965
1966
1967
1968
Fig. 12. Density of Paracalanus parvus and Corycaeus anglicus at station
21 in Yaquina Bay.
1969
I
1970
Buoy 21
Eurytemora americana
females
?\'
►ol■
," I
1 i
"63
2
0
1963
1964
I
1965
1966
1967
1968
Fig. 13. Density of Eurytemora americana at station 21 in Yaquina Bay.
1969
1970
1964
1965
Buoy 21
surface
Buoy 21
bottom
1966
1967
1968
Fig. 14. Temperatures at stations 15 and 21 in Yaquina Bay.
1969
1970
23
July and August. They are lowest in January and February. The annual
range is about 10°C from 7° to 17°C with occasional lower or high values.
The summer period is the most variable because either cool, upwelled water
from offshore or warmer, locally heated water from upstream can be present
at any given sampling time. Station 21 is more affected by local heating
in summer than station 15. Salinity (Fig. 15) is lower and more variable
in winter when the river is carrying more freshwater from the rains of that
season. From late June until October, salinities at stations 15 and 21 are
close to those in the ocean.
A distinct annual cycle does not appear in the dissolved oxygen data
(Fig. 16) until 1966. Techniques were upgraded at that time, and some of
the early data should be disregarded. Oxygen concentrations from late
November to late April have a mode of about 6.5 ml/liter.
In summer and
fall they are lower, probably because temperatures and salinities are
higher. Variability in oxygen concentration is greater in summer than in
winter. This is probably caused by oxygen production by plants in the
rich, upwelled water just offshore.
30—
20—
10—
0—
30
10—
10—
0
1963
I
1964
Fig. 15.
15.
1965
1966
1
967
l
968
Salinities at stations 15 and 21 in Yaquina Bay.
n69
1970
2
Fig. 16. Dissolved oxygen concentrations at stations 15 and 21 in Yaquina
Bay.
26
Acknowledgements
This program has been supported by grants from the National Science
Foundation (GP 622), N.S.F. Institutional Sea Grant Program G.H. 97, the
Office of Naval Research (NONR 1286(10)), the Public Health Service (1T1WP-61), and the Federal Water Quality Administration (51-1-WP-111).
Many people have participated in the collection and analysis of the
samples. Large contributors were Daniel J. Bergeron, Janet Carter, George
Crandell, Douglas Manske, Adrian Matson, Jon M. McCormick, Howard Russell,
and Owen Taylor.
Herbert Frolander initiated the program and is responsible for the
sampling plan. Joan Flynn has managed the program, and she and Sharon
Spring have counted the samples since 1966. Steven Zimmerman has coordinated
field sampling since mid-1969. Charles Miller developed the graphical data
presentation for this report.
27
References
Biological and chemical features of tidal estuaries.
Frolander, H. F., 1964.
Water Pollut. Cont. Fed., 36:1037-1048.
Frolander, H. F., 1968. Statistical variation in zooplankton numbers from
subsampling with a Stempel pipette. Water Pollut. Control Fed., 40:
R82-R88.
Gemperle, M. and K. Keeling, 1970. Geophysical data reduction and plotting
computer programs. Oregon State University Dept. of Oceanog.
Ref. 70-10. 56 pages.
Goodwin, C. R., E. W. Emmett and B. Glenne, 1970. Tidal study of three
Oregon estuaries. Bulletin No. 45 of Oregon State University Engineering Experiment Station. 39 pages.
Wiebe, P. H. and W. R. Holland, 1968. Plankton patchiness: effects on
repeated net tows. Limnol. and Oceanog., 13:315-321.