Download Data Package 1 - Zooplankton migrations June 2013

Data Package 1: Diel Vertical Migration of Zooplankton
Background:
Marine acoustics is the study of sound propagation and its behaviour in the ocean. It is
commonly used by scientists to study many biological and physical components of the sea.
Scientists study marine acoustics because sound travels more efficiently in the ocean than light;
for example, in coastal waters sunlight might only travel 5-20 metres, depending on turbidity,
whereas sound can travel up to 1000 km in the ocean.
Both active and passive sonar instruments are used by scientists to study marine acoustics:
Active Sonar
Active sonar systems both transmit and receive acoustic (sound) signals underwater. Acoustic
signals emitted by a transducer will reflect (echo) off objects and structures in the ocean and then
propagate back towards the transducer as pressure waves. The transducer measures and records
the intensity of the returning signal.
Sonar systems can either emit low or high sound frequencies, depending on what features of the
ocean are being studied. High frequency sonar provides better image resolution than low
frequency sonar; however, low sound frequencies can travel greater distances.
Applications of active sonar systems include studies of ocean-floor topography, zooplankton
migrations, sediment transport, fish populations, fish migrations, and natural processes such as
wind speed, rain rate and thunder. Sonar systems are either mounted on the side of a ship or
buoy, or deployed on the bottom of the seafloor.
Passive Sonar
Unlike active sonar systems, passive sonar systems only receive sound waves. Sound waves are
emitted from the sounds of marine mammals, shipping vessels and weather phenomena such as
wind and rain. These sounds are detected and recorded by a hydrophone (underwater
microphone) (Ocean Acoustics, 2013).
Study Location:
1. Saanich Inlet
Located on the southeastern side of Vancouver Island, Saanich Inlet is a glacially carved fjord
reaching a depth of about 230 m (Saanich Inlet, 2013). The Inlet is supplied with freshwater
from the Fraser River in the summer and freshwater from the Cowichan River in the winter
(Gargett et al. 2003). A shallow sill (70 m) located at the mouth of the inlet isolates the deep
basin from the Strait of Georgia waters. This sill, known as the Victoria Sill, restricts inflow of
neighboring oxygenated waters into the deep basin, leaving bottom waters anoxic for most of the
year (Herlinveaux, 1962). Large phytoplankton blooms occur in the spring and exhaust the
oxygen supply of deep waters (Manning et al. 2010). At certain times of the year, dissolved
oxygen conditions are so low that the benthic community composition and species behavior will
change (Matabos et al, 2012). During the spring and fall, episodic deep-water renewals bring
dense seaward water over the sill and into the deep basin replacing hypoxic and anoxic waters
(Manning et al. 2010).
VENUS Coastal Network
VENUS is the coastal cabled network
of Ocean Networks Canada, located
off the west coast of British Columbia
and is operated from the University of
Victoria. A total of three instrumented
study nodes are connected to the
shore station by a fiber optic cable;
one node is located in Saanich Inlet
while the remaining two are located
in the Strait of Georgia. The undersea
observatory collects real-time video,
hydrophone and oceanographic data,
which allow scientists to study ocean
phenomena on a continuous
timescale. For more information, visit
www.venus.uvic.ca.
Figure 1. Saanich Inlet array, part of the VENUS
Coastal Network. Image credit:
http://communications.uvic.ca/releases/release.ph
p?display=photos&id=687 (Accessed March 22,
2013)
A zooplankton acoustic profiler (ZAP) deployed on the VENUS instrument platform (VIP) in
Saanich Inlet, 100 metres below the ocean surface, routinely detects and monitors the vertical
distribution of plankton and fish. The ZAP transmits a short (~300 micro-second), high
frequency (200 kHz) pulse of sound that travels through the water column. As the sound pulse
encounters zooplankton and fish, a portion of the sound energy is reflected back and recorded by
the ZAP. The recorded sound energy is used to produce acoustic images coloured according to
the intensity of the returning sound. These images reveal the vertical migrations of zooplankton
over time (ASL Environmental Zooplankton Acoustic Profiler (ZAP), 2013).
Figure 2. ASL Environmental
Zooplankton acoustic profiler.
Data Analysis:
A total of four echo-sounder images from the Zooplankton Acoustic Profiler deployed in Saanich
Inlet (100 m) are provided in this data package. These images are produced from data recorded
on the first day of every third month (April, July, October and January) during 2012 – covering
all four seasons.
How to read echo-sounder images from the ZAP:
Key Observations:
 Changes in the initiation and timing of the zooplankton vertical migrations between
seasons.
 Differences in the intensity of the deep scattering layer (a sound – reflecting layer
caused by aggregations of animals) throughout the year. The intensity of the deep
scattering layer is proportional to the zooplankton abundance.
Data Interpretation:
 What types of stimuli are primarily responsible for the initiation and timing of the
migration?
 Why do the zooplankton exhibit vertical migrations? In other words, what is the
adaptive value of vertical migration?
 What are the potential factors that could cause changes in the zooplankton abundance
throughout the year? (i.e. food availability)
Available Data:
Figure 3. Echo – sounder image from the ASL Environmental Zooplankton Acoustic
Profiler (ZAP), deployed on the VIP in Saanich inlet (97 m), during Jan 1, 2012 [UTC].
Figure 4. Echo – sounder image from the ASL Environmental Zooplankton Acoustic
Profiler (ZAP), deployed on the VIP in Saanich inlet (96 m), during Apr 1, 2012 [UTC].
Figure 5. Echo – sounder image from the ASL Environmental Zooplankton Acoustic
Profiler (ZAP), deployed on the VIP in Saanich inlet (96 m), during Jul 1, 2012 [UTC].
Figure 6. Echo – sounder image from the ASL Environmental Zooplankton Acoustic
Profiler (ZAP), deployed on the VIP in Saanich inlet (96 m), during Oct 1, 2012 [UTC].
If you wish to access other echo-sounder images from different times follow the instructions
below.
Note: To access echo-sounder images collected by the Zooplankton Acoustic
Profiler, you must acquire an account with VENUS (if you already have an account with
|NEPTUNE Canada that will work with VENUS as well). To do so, click the link:
http://venus.uvic.ca/venus-user/register/
Accessing the Data:
1. Go to the VENUS website: http://venus.uvic.ca/
2. Click on the “Data” tab located at the top of the homepage.
3. Click on “Download Data”
4. (If you haven’t already signed in it will direct you to do so now). Under “Search Type”
click “Stationary Platform.” Then under “Stationary Platform Data” click “Search
by Instrument”
5. Under “Time Range” enter the times you are searching for in the correct format (DDMMM-YYYY HH:MM:SS).
6. Under “Location” select “Saanich Inlet”, the location of your choice and the site of your
choice.
7. Under “Instrument” select the “ASL Zooplankton Acoustic Profiler 1007”
8. Under “Sensor(s)”, “Processing”, “Metadata Format” and “Quality Control” leave all
the settings as they are. Under “Data Format” you can choose the image file type you
would like to receive – “PNG Data Plot”, “PDF Data Plot” and “MATLAB Version 7
mat file”.
9. Finally click “Search now” and an email will be sent to you when your data request is
ready.
References:
R Core Team (2012). R: A language and environment for statistical computing. R Foundation for
Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org/.
Ocean Acoustics. (2013). Retrieved March 25, 2012, from http://venus.uvic.ca/research/oceanprocesses/ocean-acoustics/.
ASL Environmental Zooplankton Acoustic Profiler (ZAP). (2013). Retrieved March 25, 2013,
from http://venus.uvic.ca/discover-venus/what-is-venus/instruments/asl-environmentalzooplankton-acoustic-profiler-zap/.
Herlinveaux R.H., 1962. Oceanography of Saanich Inlet in Vancouver Island, British Columbia.
Journal of the Fisheries Research Board of Canada. 19 (1). Pages: 1-37.
Matabos M., Tunnicliffe V., Juniper S.K., Dean C. 2012. A year in hypoxia: epibenthic
community responses to severe oxygen deficit at a subsea observatory in a coastal inlet. PLoS
ONE. 7(9):e45626, DOI:10.1371/journal.pone.0045626
Manning, C., Hamme, R.C., Bourbonnais, A. 2010. Impacts of deep-water renewal events on
fixed nitrogen loss from seasonally-anoxic Saanich Inlet. Marine Chemistry. 122(1-4). Pages: 110.
Gargett, A.E., Stucchi, D., Whitney, F. 2003. Physical processes associated with high primary
production in Saanich Inlet, British Columbia. Estuarine Coastal and Shelf Science. 56(5-6).
Pages: 1141-1156. DOI: 10.1016/S0272-7714(02)00319-0
Saanich Inlet. (2013). Retrieved March 16, 2013, from http://venus.uvic.ca/discovervenus/where-is-venus/saanich-inlet/
Further Reading:
Hernandez-Leon, S; Portillo-Hahnefeld, A; Almeida, C. 2001. Diel feeding behavior of krill in
the Gerlache Strait, Antarctica. Marine Ecology Progress Series. 50 (4). Pp. 235-242.
Li, M; Gargett, A; Denman, K. 2000. What determines seasonal and interannual variability
phytoplankton and zooplankton strongly estuarine systems? Application to semi-enclosed
estuary of Strait of Georgia and Juan de Fuca Strait. Estuarine Coastal and Shelf Science. 50(4).
Pp. 467-488.
Beklioglu, Meryem; Gozen, Ayse Gul; Yildirim, Feriha. 2008. Impact of food concentration on
diel vertical migration behavior of Daphnia pulex under fish predation risk. 614(1). Pp. 321-327.