Oviposition by water bugs (Hemiptera: Corixidae) induces changes in dissolved oxygen and turbidity measurements in Thomsons Lake, Western Australia

7 Pages·1996·1.5 MB·

by  Mark C Bailey

OVIPOSITION BY WATER BUGS (HEMIPTERA: CORIXIDAE)
INDUCES CHANGES IN DISSOLVED OXYGEN AND
TURBIDITY MEASUREMENTS IN THOMSONS LAKE,
WESTERN AUSTRALIA.
By MARK C BAILEY and DAVID R HAMILTON
Centre for Water Research, University of Western Australia,
Nedlands, Western Australia 6907.
ABSTRACT
In a sequence of data recorded at 15 minute intervals in a shallow
iakein Western Australia, marked stepsupward in turbidity and a
significant drop in dissolved oxygen coincided with a period of
oviposition by aquatic Hemiptera (Corixidae). It is proposed that
the steps in the turbidity data reflect the times of oviposition and
that the drop in dissolved oxygen can be attributed to respiration
by the Corixidae.
INTRODUCTION information about the organisms
responsible for the fouling.
In recent years the collection of large
In a study conducted between 1
quantities of data with a high degree
August 1994 and 29 November 1994,
of spatial and temporal resolution has
data were collected from the shallow
becomecommonplace in lakes due to
Thomsons Lake at 15 minute
advances in the technology associated
intervals continuously over periods
with instrumentation and data
ranging from 3 to 10 days. The
storage (Imberger, 1994). The instru¬
objectiveof this study was toexamine
ments are generally not deployed
therelationshipsbetween wind, light,
underwater for extended periods of
fluorescence and physical properties
time, as fouling from biological
of the water column over short time
activity and deterioration of the
scales. During a 5 day data collection
equipment compromises the
period in November 1994 an
accuracy of the readings. In instances
oviposition event caused fouling of
of prolonged data collection,a regular
the instruments.Theeventcoincided
schedule of maintenance and
with anomalous measurements of
recalibration is usually required to
dissolved oxygen and turbidity in the
keep measurement errors to a
lake on 17 and 18 November 1994.
minimum. If there is a fouling event
between instrument checks the data Identification of the eggs (see Fig.2)
set may be useless for the original indicated that they were deposited
purposes of the study. Alternatively, by an aquatic water bug of the family
such an event may provide Corixidae (Hinton, 1981; CSIRO. 1991).
123
Figure 1. Location and bathymetry of Thomsons Lake. The data in this paper was collected
at the station marked (X).
The closely packed eggs were attached (Kirkaldy) and Micronecta robusta
to the surface of submerged plants (Hale).
and objects by the stalks. Voucher
specimens of these eggs have been
preserved at the Department of DESCRIPTION OF STUDY SITE
Zoology of the University of Western Thomsons Lake (Fig. 1), is shallow
Australia. A macroinvertebrate moni- (maximum depth - 1.5 m), flat bot¬
toring program conducted in tomed and approximately circular
Thomsons Lake in October 1994 (diameter -1600 m). The lake is 20 km
(Cheal &. Davis, 1995) also confirmed south of Perth. Western Australia and
the presence of at least two species of
7 km inland from the Indian Ocean.
Corixidae, Agraptocorixa eurynome It is primarily a surface expression of
124
the water table but it is also fed by location shown in Fig. l.This platform
some very small surface tributaries was used for the deployment of a
that enter the lake through the Grant/Yellow Springs Instruments
surrounding rush beds. The lake (YSl) model 3800 SONDE and logger
forms a part of a large chain of at a depth of 0.9 m. This instrument
wetlands on the Swan Coastal Plain, was used to measure dissolved oxygen,
described by Balia (1994). It is presently turbidity, pH, temperature and
considered to be becomingeutrophic, conductivity. The dissolved oxygen
due in part to pressure from urban¬ probe was equipped with a
isation (Cheal & Davis, 1995). mechanical stirrer which vibrated
vigorously and as a consequence the
membrane of the probe was prevent¬
MATERIALS AND METHODS ed from becoming fouled. Turbidity
is a measurement of the scattering of
A small platform was erected above
light in the water column. In the
the waterline in 1.4 m of water at the
turbidity probe a light signal passes
through a bundle of optic fibers and
the reflected back scatter of light is
measured via the same optic fibers.
Any foulingoftheendsof these fibers
would result in an increase in the
measured turbidity proportional to
the amount of fouling. The increase
in measured turbidity would remain
until the sensors were cleaned.
RESULTS AND DISCUSSION
On 15 November 1994 (day 319) it was
noted that a small number of eggs
had been laid on the platform legs
below the water level. On a return
visit on 22 November 1994 (day 326)
the probes in the SONDE were found
to be fouled with eggs with the
exception of the vibrating dissolved
oxygen probe. The platform legs
below the water level were also
thickly coated with eggs. Figure 3
shows the probes and the probe
housing after the egg laying event,
there are a large number of eggs
attached to the probe housing. The
Figure 2. Unhatchcd eggs (Hemiptera:
turbidity probe is visible in the
Corixidac) taken from the YSI/SONDE
probe housing. The diameter of theeggs is foreground.Thereweresomeeggslaid
approximately 0.6 - I mm and the stalk on the surface of the optic fiber
length isapproximately 1 mm. bundle which is 6 mm in diameter.
125
Because the turbidity probe is small, a
single egg (0.6 - I mm diameter) laid
on the bundle of optic fibers would
be sufficient to cause a step up in
turbidity readings.
Figure 4 shows a discontinuous
sequence of turbidity data measured
betweenday296and326.Theincrease
in turbidity between day 306and day
318 was a result of an increase in
phytoplankton concentration and
matched corresponding increases in
chlorophyll a and light attenuation
(Bailey and Hamilton, in press). How¬
ever, the most prominent feature of
thefigureisthefourstepped increases
in turbidity, commencing at the end
of day 320. The large jumps in
turbidity measurements were caused
by eggs bei ng laid on the exposed ends
the optical fibers of the turbidity
probe. Because turbidity was recorded
at 15 minute intervals, the times at
which clusters of eggs were laid can
easily be determined. Higher
Figure 3. The YSl/SONDE probe. 22 resolution turbidity measurements
November, 1994. Clusters of eggs can be together with other relevant
seen attached to the probes and the probe parameters give a more complete
guard (top). The turbidity probe is foremost picture of the fouling event. In Fig.
and the dissolved oxygen probe is to the
5a, the first step in turbidity occurs
left of the turbidity probe
1994 Julinn Day
Figure 4. A sequence of turbidities measured at 15 minute intervals in nephelometric
turbidity units (NTU). The effects of fouling on turbidity probe measurements are
Illustrated by the values recorded after day 320.
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D
H
2
15
3
H
1994 Julian Day
Figure 5. Physical data sequences pertaining to the oviposition event, day 319 to day
324 of 1994 {16 November to 20 November); (a) the fine line is wind speed 10 m above
water surface (ms’) and the heavy line is turbidity at a depth of 0.45 m. in
nephelometric turbidity units (NTU): (b) the fine line is light intensity measured 0.3 m
below the water surface (pEm ^s') and the heavy line is dissolved oxygen (mgl') at a
depth of 0.45 m.
just before 24:00 h on day 320, larger concentration in Thomsons Lake
steps occurred in the half hour showed a diurnal cycle typical of
following sunset on day 321 and after productive lakes (Fig. 5b). The
sunset the following evening of day dissolved oxygen concentrations
322 and the last recorded step occurs would reach a maximum prior to
late in the evening (21:00 h) of day dusk due to the photosynthetic
324. The implied rhythm of activity of the phytoplankton, and a
oviposition is circadian, which is minimum prior to sunrise due to
similar to thatobservedin many other respiration (George.1961; Wetzel, 1983).
insect species (Saunders. 1982). There were long term drifts in the
Turbulent conditions did not appear dissolved oxygen concentration due
to have an effect on the egg laying as to growth and mortality of phyto¬
thermistor chain data showed that plankton populations (chlorophyll a
the lake was isothermal vertically, concentrations ranged from 20 pg/L
experiencingfully turbulent mixing to 67 pg/L), changes in water
on days 322 and 323, with wind speeds temperature (range: 15 °C to 26 °C),
at 10 m height exceeding 5 ms ' (see Fig. mixing events and gradual deterior¬
5a). ation of the oxygen probe membrane.
Measurements of dissolved oxygen However, we have no previous
127
recorded instances of an overnight 322 and that the drop in dissolved
depression of the scale of the one oxygen on this day was a highly
observed at Thomsons Lake in the localised event, due solely to a swarm
early morning of 18 November (day of Corixidae present in and around
322). the probe housing which laid the
During the time of the oviposition bulk of the eggs seen in Figure 3.
Further steps up in turbidity on
event the lake flora was dominated
by two algal species. Microcystis subsequent days were due to a
aeruginosa, which was increasing in continuation of the oviposition with
concentration, and Anabaena acircadianrhythm.albeit at a reduced
circinalis, which was abundant but level of activity. The turbidity data
declining in concentration (Bailey only allows us to comment when
and Hamilton, in press). This steps occurred and theabsenceof steps
depression is not explained by the in turbidity data on days 323 and 324
collapse of a phytoplankton bloom doesn’t necessarily imply an absence
as the dissolved oxygen values return of oviposition. The probe is small and
to the longer term trend in the period the probability of eggs being deposited
following day 322. A large collapse of on it is obviously reduced if few
a bloom and the associated oxygen Corixidae are present.
uptake would have had a longer term The time of the largest recorded
effect on the measured con- oviposition event also coincided with
centrationsofdissolved oxygen in the a full moon on 18 November, 1994
lake. (day 322) which could be due to the
We believe that the depression in Corixidae sharing a trait with other
dissolved oxygen is symptomatic of aquatic insects in exhibiting
increased uptake due to respiration periodicity with the moon. e.g.,Povilla
of the aquatic biota. In this instance adusta (Corbet et al., 1974) and Clunio
we attribute it to the presence of the marmus (Neumann, 1976). However,
Corixidae, which have the ability to there is no evidence in the literature
remain submerged for sustained to support this as a feature of
periods by breathingair from a bubble Corixidae behaviour, nor is there any
trapped against their body. This obvious environmental or evolution¬
bubble functions as a physical gill, ary explanation.
theoretically capable of drawing
nearly 13 times the original oxygen
volume from the surrounding water CONCLUSION
through the bubble surface. Reviews
A sequence of data collected from
of this mechanism can be found in
instruments fouled by an oviposition
Hinton (1981) and Ward (1992). As the
event from water bugs of the family
drop in dissolved oxygen occurs at a
Corixidae has provided insight into
period when the turbidity data
theecologyof thebugs.Turbiditydata
suggests that oviposition was occur¬
suggest that oviposition occurred
ring, this explanation seems the most
with a circadian rhythm and that the
plausible.
preferred timeforoviposition was the
We postulate that the majority of the evening. Turbulent conditions did
eggs were laid on the probes during not appear to impede oviposition. An
the oviposition event recorded on day abnormally large drop in dissolved
128
oxygen concentration on one night southern Beeliar wetlands for the
is best explained by an increase in south Jandakot drainage scheme en¬
respiration due to oviposition by large vironmental management program.
numbers of water bugs near the Water Authority of Western Aus¬
oxygen sensor, the insect drawing tralia Report, Jan. 1995.
oxygen from the surrounding water
Commonwealth Scientific and
using its attached air bubble as a
Industrial Research Organisation
physical gill.
(CSIRO), 1991. The Insects of Australia.
Melbourne University Press, Mel¬
ACKNOWLEDGEMENTS bourne, 1137pp.
CORBET. S. A.. SELLICK. R. D.. &
The photograph for Fig. 2 was taken
WILLOUGHBY, N. G.. 1974. Notes on
by Wasele Hosja of the Waterways
the biology of the mayfly Povilla
Commission of Western Australia.
We thank Winston Bailey and Don adusta in West Africa. J. Zool. Lond.
Edward. Zoology Department, Uni¬ 172: 491-502.
versity of Western Australia for GEORGE, M. G., 1961. Diurnal
identification and useful comments variations in two shallow ponds in
on the manuscript. We also thank Delh i, India. Hydrohiologial8;265—273.
Jenny Da vis of the School of Biological
HINTON, H. E., 1981. Biology of insect
and Environmental Science.
eggs. Pergamon Press, Oxford, 1125pp.
Murdoch University for her
comments on the manuscript. IMBERGER, J., 1994. Transport pro¬
cesses in lakes: A review. In R.Margalef
(ed.), Limnology noty; A paradigm of
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