RV Kirby Report
Influence of Physical Environment
on
Copepod Abundance
Lily Munsill
23 May 2014
MB3050
Biological Oceanography: Kingsford
Abstract
The physical environment can influence distribution of copepod abundance and
affect distributions of small and large copepods. This study specifically looks at
the influence of oceanography on the distribution of large calanoid copepods and
their juvenile forms, copepodites. Plankton samples were taken along a transect
of Cleveland Bay at three distances from the shore, at four different tidal stages,
two of which (flood-full and full-ebb) were repeated. A Neuston tow and small
phytoplankton net were used to sample ocean surface for phytoplankton, and a
CTD and Niskin bottle were used for stratified depth samples to measure
temperature, salinity, and density in the water column. Abundance of total
calanoid copepods (mean total of small calanoid copepods + mean total of large
calanoid copepods) generally correlated with the sinusoidal wave of the tidal
stage, peaking at high tide and decreasing with lower tide, especially at the outer
transect location, confirming that copepod abundance is influenced by tide and
also varies with distance from shore. Copepod abundance was highest where the
temperature and salinity were well mixed throughout the water column.
Abundance was lowest at highest salinity.
Introduction
Understanding how the physical environment influences distribution of
abundance of copepods is important in understanding population dynamics of
copepods and is useful information for fisheries. This study looks at the influence
of temperature, salinity, and density on copepod distribution in addition to
distribution through different tidal stages at three different distances from the
shore in Cleveland Bay, off of Townsville, QLD. Tidal stages include flood-full,
full-ebb, ebb-low, and low-flood.
Temperature is a key influence on population dynamics of copepods
(Devreker et al. 2009). Temperature affects salinity which also influences
copepod abundance (Daase et al. 2007). Food abundance can also influence
distribution of copepods (Durbin et al. 1992). Abundance of different sizes of
copepods can be attributed to predation pressures, salinity, and tidal flow.
This paper will explain methodology of our study, and present results of
different size classes and types of copepods and plankton in relation to tidal
stages and distance from shore. Additionally, data on temperature, salinity, and
density profiles with depth will be presented at different tidal stages and
distances from the shore in order to examine the influence of oceanography on
copepod size distribution.
Methods and Materials
Sampling sites were along a transect in Cleveland Bay, at three distances
from the shore, to be known as “outer”, “mid”, and “inner”. Samples were taken
at different tidal stages, and sampling methods were repeated twice per site on
the transect. In total, there were six different sampling events of Cleveland Bay.
On Sunday, March 2nd, the three locations along the transect were sampled four
times throughout the day at the following tidal stages: flood-full, full-ebb, ebblow, low-flood, and on Wednesday, March 5th two additional transects were
sampled during flood-full and full-ebb tides.
Figure 1 Cleveland Bay sampling area, off the coast of Townsville, QLD and Magnetic Island.
Tools for plankton sampling were a Neuston tow and a phytoplankton tow. Tools
used to collect oceanographic data were a CTD device, a messenger activated
Niskin bottle, a glass thermometer and a refractometer.
Neuston tow: A Neuston net was used to sample for macro-zooplankton along
the surface. The Neuston net was a skinny net with a large rectangular opening
and an attached plankton collecting holder, it was attached to the trawling beam
of the RV Kirby and was lowered in the ocean by a team of two to three people,
one holding the front of the net and the depressor, the others holding the
collector and the mesh. The net was actively dragged along the surface at 2 knots
for five minutes. After five minutes, the Neuston net was towed in, the contents
of the holder were emptied into a seine to be filtered, and filtered contents were
stored in a sample jar with 10% formalin for preservation of plankton samples.
This procedure was performed twice for each of the three locations along the
transect. A flow meter was attached to the Neuston tow to calculate total water
volume sampled.
Phytoplankton tow: The phytoplankton tow, also known as the microzooplankton net was used for sampling of micro-zooplankton and phytoplankton
along the surface. The net, with a smaller rectangular opening and a plankton
container attached, was lowered into the ocean and was let out 10 meters from
the stern of the vessel, and slowly pulled back in along the surface. The container
was retrieved, emptied and filtered through a sieve; the filtered contents were
placed in sample jars with 10% formalin to preserve samples. This procedure
was performed twice for each of the three locations along the transect.
CTD: The CTD device was used to measure temperature and salinity along a
depth profile through the water column. The CTD device was used when the
vessel was immobile. The device was held at the surface of water for 60 seconds
to calibrate. After calibration, the CTD was lowered to the bottom at
approximately 1 meter per second; data was retrieved at a later time.
Niskin bottle: The Niskin bottle was used to measure salinity and temperature in
waters 1 meter below the surface and just above the ocean floor. The vessel’s
depth finder was used to note depth to prevent dropping the Niskin bottle all the
way to the ocean floor which would create turbidity and cause collection of
unnecessary sediment. The trigger mechanism was set up on the device before
deployment. The device was lowered approximately a meter below the surface,
the messenger weight was released and the water sample collected was poured
into a bucket where temperature was measured with a glass thermometer.
Salinity was measured from the sample using a refractometer. 2 liters of the
sample was filtered to collect depth-stratified water samples for chlorophyll; the
filtered material was added to a solution with 10% formalin. Procedure was
repeated at half a meter above the ocean floor.
Abundance of copepods were counted in the laboratory. Taxonomy was sourced
from the MB3050 laboratory manual.
Results
# Snall Calanoid copepod per m^3
Small Calanoid Copepod Abundance
14
12
10
8
6
Outer
4
Mid
2
Inner
0
Flood-Full
Full-Ebb
Ebb-Low Low-Flood Flood-Full
(2)
Stage of Tide
Full-Ebb
(2)
Figure 2 Mean small calanoid copepod abundance per cubic meter at three distances from the shore
with varying stages of tide.
Small calanoid copepod abundance per m3 was highest at outer transect during
flood-full tide. However, in the second flood-full sampling, abundance was
highest at the mid transect. Abundance was also notably high in the outer
transect during ebb-low tide. Abundance along the transect distances had little
variance during full-ebb and low-flood tides. (Figure 2).
# Large Calanoid Copepod per
m^3
Large Calanoid Copepod Abundance
14
12
10
8
6
4
2
0
Outer
Mid
Inner
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood Flood-Full Full-Ebb (2)
(2)
Stage of Tide
Figure 3 Mean large calanoid copepod abundance per cubic meter at three distances from the shore
with varying stages of tide.
Large calanoid copepod abundance per m3 was lowest during ebb-low and fullebb (2) tides. There were consistently lowest numbers of large calanoids in the
inner transect compared to the mid and outer, except for low-flood tide where
the mid transect had the lowest abundance of large calanoids (Figure 3).
# Total Calanoid Copepod per m^3
Total Calanoid Copepod Abundance
18
16
14
12
10
8
6
4
2
0
Outer
Mid
Inner
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full Full-Ebb (2)
(2)
Stage of Tide
Figure 4: Mean total calanoid copepod abundance (mean small calanoid + mean large calanoid) per
cubic meter at three distances from the shore with varying stages of tide.
Patterns in the total calanoid copepod abundance per m3 largely reflect patterns
found in the small calanoid copepod abundance. Highest abundance of calanoids
was consistently in the outer transect, except during full-ebb (2) tide. Abundance
seems to correlate with the tide, at all locations along the transect, peaking at
flood to full, and as the tide goes out total calanoid copepod abundance
decreases, and increases again as the tide starts to come in (Figure 4).
# Small Calanoid Copepods per L
Small Calanoid Copepod Abundance (2)
25
20
15
Outer
10
Mid
5
Inner
0
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full Full-Ebb (2)
(2)
Stage of Tide
Figure 5: Mean small calanoid copepod abundance sampled with zooplankton fine mesh. Abundance
measured as # per liter, and sampled at three distances from the shore with varying stages of tide.
Small calanoid copepod abundance per L was highest at the inner transect
during full-ebb and ebb-low tides. In the full-ebb tide abundance did not vary
between the outer and mid transect. Abundances were smallest at the mid
transect, especially during low-flood and flood-full tides (Figure 5).
# Large Calanoid Copepod per L
Large Calanoid Copepod Abundance (2)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Outer
Mid
Inner
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full Full-Ebb (2)
(2)
Stage of Tide
Figure 6 Mean large calanoid copepod abundance sampled with zooplankton fine mesh. Abundance
measured as # per liter, and sampled at three distances from the shore with varying stages of tide.
Large calanoid copepod abundance per L was low compared to small calanoid
abundance. The highest abundance occurred during the flood-full (2) tide at the
inner transect, however during all other tidal stages, the abundance at the inner
transect was low to none (Figure 6).
# Copepodites per L
Copepodite Abundance
10
9
8
7
6
5
4
3
2
1
0
Outer
Mid
Inner
Flood-Full Full-Ebb
Ebb-Low Low-Flood Flood-Full Full-Ebb
(2)
(2)
Stage of Tide
Figure 7 Mean copepodite abundance sampled with zooplankton fine mesh. Abundance measured as
# per liter, and sampled at three distances from the shore with varying stages of tide.
Copepodite abundance per L was highest at the outer transect during low-flood
and flood-full tides. There was no presence of copepodite at full-ebb tide. Also
notable, there were consistent abundances at flood-full tide at all distances along
the transect (Figure 7).
Cyclopoid Copepod Abundance
# Total Cyclopoid Copepods per L
4
3.5
3
2.5
2
Outer
Mid
1.5
Inner
1
0.5
0
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full Full-Ebb (2)
(2)
Stage of Tide
Figure 8 Mean cyclopoid copepod abundance sampled with zooplankton fine mesh. Abundance
measured as # per liter, and sampled at three distances from the shore with varying stages of tide.
Total cyclopoid copepod abundance per L was variable with transect distance.
Highest abundance occurred at the outer transect during low-flood tide (Figure
8).
# Harpacticoid Copecod per L
Harpacticoid Copepod Abundance (fine
mesh)
7
6
5
4
3
Outer
2
Mid
1
Inner
0
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full
(2)
Full-Ebb (2)
Stage of Tide
Figure 9 Mean harpacticoid copepod abundance sampled with zooplankton fine mesh. Abundance
measured as # per liter, and sampled at three distances from the shore with varying stages of tide.
Harpacticoid copepod abundance per L was relatively low. High abundances
occurred during low-flood tide at the outer transect and during full-ebb tide at
the mid transect (Figure 9).
Total Small Copepod Abundance
# of Small Copepods per L
25
20
15
Outer
10
Mid
5
Inner
0
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Flood-Full
(2)
Full-Ebb (2)
Stage of Tide
Figure 10 Total small copepod abundance small calanoid copepod + copepodite abundance)
sampled with zooplankton fine mesh. Abundance measured as # per liter, and sampled at three
distances from the shore with varying stages of tide.
Total small Copepod abundance (small calanoid copepod + copepodites)
followed similar patterns to small calanoid copepod abundance. High
abundances occurred along the inner transect. Abundance remained consistent
along the entire transect during flood-full tide and full-ebb (2) tide (Figure 10).
# of Macrozooplankton per 100m^3
1600
Total Macrozooplankton Abundance
1400
1200
Outer
1000
Mid
800
Inner
600
400
200
0
Flood-Full
Full-Ebb
Ebb-Low
Low-Flood
Stage of Tide
Flood-Full (2) Full-Ebb (2)
Figure 11 Total mean macrozooplankton abundance per 100 cubic meters. Totals come from sums
of mean total elongate zooplankton, gelatinous plankton, and fish larvae. Sampled at three distances
from the shore with varying stages of tide.
Total macrozooplankton encompasses fish larvae, gelatinous plankton, and
elongate zooplankters, and abundance is presented as # per 100 m3. The highest
abundance was during the low-flood tide, along the mid transect. Except for the
low-flood tide, abundance was always lowest along the inner transect (Figure
11).
Figure 12: Temperature, salinity and depth profiles at various stages of the tide and various
distances from shore; green depicts inner, red depicts mid, and blue depicts outer transect. Profiles
from left to right: temperature depth profiles, salinity depth profiles, and density depth profiles.
Discussion
Patterns of copepod abundance are not present for all tides, however,
generally the highest abundances occur most often during flood-full or full-ebb
tides, so highest copepod abundance occurred around high tide. At flood-full tide,
abundance was highest for small calanoid copepods (sampled with larger mesh)
and also for total calanoid copepods (Figure 2, Figure 4). Abundance of total
calanoid copepods (mean total of small calanoid copepods + mean total of large
calanoid copepods, sampled with large mesh) seemed to correlate with the
sinusoidal tidal waves, especially at the outer transect location. Abundance
peaked at flood-full and as the tide ebbed the total calanoid copepod abundance
decreased, and increased again as the tide started coming in (Figure 4). This
suggests that the source of copepods to Cleveland Bay is from deeper waters, not
inshore.
There was no large difference of abundance with respect to distance from
shore between the small and large calanoid copepod sampled with larger mesh
(abundance recorded as # per cubic meter). At the mid transect small calanoids
were slightly more abundant, but had similar abundances to large calanoids at
the outer and inner transects (Figure 2, Figure 3). Data from the finer mesh
sampling (abundance recorded as # per L) shows much lower abundance in
large calanoid copepods at all tidal stages and distances from shore. Relative
abundance was highest in large calanoids at flood-full tide along the inner
transect and abundance for small calanoids was also at its highest along the
inner transect, but during full-ebb tide (Figure 5, Figure 6). The high abundance
along the inner transect and during flood-full tide also suggests the source of
copepods is from outer ocean sources as the tide brings in copepod rich waters
all the way inshore. Low abundances at further distance from shore could be
contributed to higher predation pressures.
Copepodite, the juvenile form of copepods, had highest abundance at the
outer transect during low-flood and full-flood tides. There were very little or no
copepodites present at full-ebb tide along all distances of the transect. As tide
starts ebbing out, it starts increasing salinity (Figure 12) which could have an
impact on copepodite abundance, suggesting they have low tolerance for high
salinity.
We can also examine the depth profiles of temperature, salinity, and
density to explain plankton abundance. Generally, highest abundance was during
flood-full or full-ebb tide, at the outer transect. Patterns during flood to full tide
at the outer transect show slightly cooler temperature that was constant through
the water column, constant salinity and constant density through the water
column (Figure 12). This suggests that highest abundance of plankton at the
surface is related to the well mixed depths, providing ideal conditions for
copepod recruitment and food. At full-ebb tide the temperature was less
constant through the water column and there was a clear thermocline at the
outer transect, however salinity and density appeared to remain constant
(Figure 12). This also supports that copepods are more abundant with well
mixed waters, as they would have more nutrients.
Tidal stages where copepod abundance was relatively low was at ebb-low.
During the ebb-low tide, it appeared that all areas were very well mixed and
showed similar salinity through depth, but salinity was relatively high compared
to other tidal stages, especially at the outer transect (Figure 12). During ebb to
low, the tide is ebbing out, bringing less fresh water to the outer sites. This had a
negative impact on copepod abundance, suggesting low tolerance of copepods to
relatively high salinity.
Large error bars in mean abundances of all classifications of copepods
and macrozooplankton can be attributed to the variable techniques by different
people who counted plankton in the laboratory. Additionally differences in the
abundances of copepods in the repetitions of flood-full and full-ebb tides can be
attributed to the different days of sampling. Higher samples of tide repetition
could be useful in the future for obtaining more accurate abundance patterns in
respect to tidal stages.
References
Devreker, D. Souissi, S., Winkler, G., Forget-Leray, J., and Leboulenger, F. 2009.
"Effects of Salinity, Temperature and Individual Variability on the Reproduction
of Eurytemora Affinis (Copepoda; Calanoida) from the Seine Estuary: A
Laboratory Study." Journal of Experimental Marine Biology and Ecology 368: 11323.
Daase, M., Vik, J.O., Bagoien, E., Stenseth, N.C., and Eiane, K. 2007. "The Influence
of Advection on Calanus near Svalbard: Statistical Relations between Salinity,
Temperature and Copepod Abundance." Journal of Plankton Research 29: 903-11.
Durbin, E.G., and Durbin, A.G. 1992. "Effects of Temperature and Food
Abundance on Grazing and Short-term Weight Change in the Marine Copepod
Acartia Hudsonica." Limnology and Oceanography 37: 361-78.