WALLACE RESOURCE LIBRARY
Lecture 05 – How to Survey a Coral
Reef
This is an ‘example’ of a lecture that is given to A level students as part of their
academic lecture series whilst on their expedition.
It has been produced for the exclusive use of the lecturer conducting the series
and is solely intended for educational purposes.
Most of the material comes from Operation Wallacea sources and any other
material that has been used has been credited (as far as is possible) to the
appropriate author wherever possible.
This lecture is only to be used for EDUCATIONAL purposes.
WALLACE RESOURCE LIBRARY
Lecture 05 – How to Survey a Coral
Reef
Lecture 5 – How to survey a coral reef
Summary
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Why do we survey coral reefs?
Which method(s) to use?
Rapid habitat surveys
Benthic and invertebrate assessment techniques
Fish assessment techniques
Measuring abiotic factors (remember those??)
The use of technology
The Operation Wallacea reef monitoring program
Why do we survey coral reefs?
According to the “Status of Coral Reefs of the World: 2008”…
• 19% of the world's reefs are effectively lost already
•15% are seriously threatened with loss in the next 10-20 years
•20% are under threat of loss in the next 20-40 years.
Surveying and monitoring allows researchers and conservation
managers to quantify the state of a coral reef, and decide what
action, if any, is needed
Assessing a coral reef
•
One of the most commonly carried out assessment of reefs is a Rapid
Environmental Assessment (RAE) – known as a Survey
•
Aims to determine the overall community diversity and health of a particular
reef system at a particular time
Gradient of ecosystem health
•
By repeating environmental assessments regularly, ecosystem change
can be identified – this is known as ecosystem Monitoring
•
Operation Wallacea programme is a great example of this
Choosing the best method will depend on…
The Site:
A more remote site will
mean extra considerations
about the surveying options
available to you
Manpower:
How many people are available
to you? How can you use their
time most effectively?
The experience of the researchers:
Some techniques require a higher
level of expertise, and so the level of
training researchers have had is an
important consideration
Technique
used depends
upon…
The time available for the study:
The more time you have, the
more in depth surveying you can
do. You need to maximise the
amount of data you collect
The objectives of the study:
What questions are you trying
to answer? Is there an aspect
of the coral reef which you are
particularly interested in?
Funding:
Some methods cost more than
others, plus remember that time
costs money!
Broad habitat surveys
• For rapid characterisation of
general habitat
characteristics i.e. a “look
see”
• Large area surveyed quickly
but data is low quality
• Suitable for inexperienced
researchers
• Often used to identify areas
worth surveying in more
detail
Site: Buoy 1, Australia
Date: 1st August 2012
Reef depth estimate: 4 – 30m
Hard coral cover: 60%
Soft coral cover: 20%
Sand cover: 10%
Dominant coral growth type: Massive
Signs of bleaching? No
Signs of damaged coral? Yes
No. Diadema: 21
No. CoTs: 35
No. giant clams: 5
Example data sheet for broad habitat survey
Broad habitat survey: Manta tow
• A snorkeller is pulled behind a
slow moving boat using a
manta board
• The distance covered is noted
• Researcher notes key features
of the reef below them
Fun technique – which helps
encourage people to get
involved!
Broad habitat survey: Spot surveys
• These involve descriptive
surveys of reef habitats as
recorded on set timed spot
dives
• The information gained is broad
but enables key locations to be
identified for further study
Spot survey
results from
Puerto Rico,
Caribbean
(Morelock et al. 2001)
Benthic surveys
• Benthic means ”living on the sea bottom”
• This includes things like coral and algae, and also those fish and
invertebrates that live on the bottom
• In terms of surveys, it generally refers to space competitors (hard
coral, soft coral, benthic algae, sponge etc.)
Working close to the reef – considerations!
Diver damage can be one of the biggest threats to coral reefs
Important we think while we dive – we are trying to make
things better not worse!
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Good buoyancy – will allow you to ‘hover’ above the reef without contact
Horizontal swimming – helps prevent kicking the reef while finning
Dangling equipment – keep all kit tucked in, so it doesn’t hit the reef
Never touch the reef unless you have to – if you have no choice, only
use one finger on bare rock to push yourself away
• Bubble awareness – bubbles can damage the reef, so avoid swimming
under overhangs or into caves
• Dangerous organisms – be aware when near the reef, and waft before
using the ‘one finger rule’
• Buddy contact – maintain good buddy contact at all times
Benthic transects
Transects
1.
Line Intercept Point: Transect is laid
out (10 - 50m long) which is marked at
set intervals (10 - 100cm) along the
transect. At each interval the
substratum type underneath each
interval is recorded
2.
Continual: Substratum type lying
under every part of the tape is
recorded. Any change is recorded as
transition points
Note that both of these can be done using
videography, where a recording of the
transect is taken and analysed later
Benthic transects
Continuous
Transect
Line Intercept Point
Soft Coral
Soft Coral (8cm)
20cm
Hard Coral
Hard Coral (22cm)
20cm
Soft Coral (13cm)
Soft Coral
20cm
Sand (30cm)
Sand
20cm
Soft Coral
20cm
Soft Coral (47cm)
Soft Coral
20cm
Soft Coral
Methods of assessment
Quadrats
• Obtain quantitative data
• Size and number of replicates
depends on habitat, time available
and target organisms
• Example: 1m x 1m to calculate %
benthic cover using photo analysis
Benthic quadrats
?%
?%
?%
?%
?%
?%
Benthic quadrats
Specific benthic monitoring – coral bleaching
• Bleaching is a major problem on reefs
(discussed in a later lecture)
• Coral Watch Health Charts provide a
basic method of identifying bleaching
• Users upload results into a central
database which monitors global patterns
in bleaching
• Great tool to raise awareness and provide
basic data
• However, there are some limitations to
this technique
e.g. assumes all bleaching is lethal
Fish surveys
This is an example of swimming along a reef – how would you
recommend the fish community could be ACCURATELY surveyed?
Methods to survey fish
Destructive
Destructive techniques
remove fish and generally
kills them
VS
Non-destructive
Non-destructive techniques
do not remove or harm fish
in any way
Traps, nets, hook and line,
rotenone (anaesthetic)
Underwater visual census- divers,
video cameras
Useful for some technical data (e.g.
growth rates), but not used
otherwise as it requires fish to be
killed. Sometimes fishermen will
allow their catches to be examined.
Limits the data available, but has
little or no impact on the fish
community or the reef itself. This is
therefore the preferred approach.
Fish survey: Spot surveys
• For larger pelagic species, which will
tend to disappear soon after the
arrival of the survey team
• First person in the water
immediately looks for and records
the presence of pelagic fish species
(for a set time)
• Often such spot surveys are
completed prior to a more detailed
survey
Fish transects (also for invertebrates)
1.
Belt transects: Transect laid
down and organisms survey
either side of the transect for a
set distance e.g. 2m either side
and above
2.
Time restricted transects:
These do not use a transect
tape, but involve swimming
along the reef at a constant
speed for a set time, noting
down all fish seen. An estimate
of the area covered is then
made
25m
2m
2m
A transect (black) with the
imagined “belt” (red)
Stereo-video
• Recent development to survey fish
• Twin video camera to provide a
stereo-recording
• Allows species ID and fish lengths to
be analysed post-dive (fish lengths
are important to calculate biomass)
• Expensive but highly accurate
• High quality data can be collected
without much experience or
expertise
Stereo-video – Specialised software
Stereo-video VS Underwater Visual Census (UVC)
UVC
Stereo-video
Abundance data
✓
✓
Diversity data
✓
✓
Length data
✗
✓
Per m2 data (true)
✗
✓
Cross checking data
✗
✓
Length error
Up to 30-40%
< 5%
Survey boundary
✗
✓
Multiple observers
Increases Error
✓
Field time
More ($$$)
Less ($)
Equipment cost
Less ($)
More ($$$)
Transects per dive
2-4
10-12 +
Post dive analysis
Simple data entry
Lengthy analysis
Permanent record
✗
✓
Lets not forget our abiotic factors…
• So far in the lectures, you should
have noticed how coral reefs are
hugely dependent on
environmental factors
• These include light, temperature,
sedimentation and nutrients
• These factors can also be
monitored using various
techniques
Monitoring abiotic factors
Water Quality
• Inorganic nutrients such as nitrate,
phosphate and ammonium can stimulate
algal growth
• Simple tests can be used to measure the
levels of these nutrients in the water
Temperature and Light
• HOBO loggers (right) can be cemented to
the reef, and they will take a temperature
and light reading every second for several
years!
• They can then be brought up and the data
downloaded onto a computer
Monitoring abiotic factors
Turbidity
• Can be measured by filtering large
volumes of water and weighing the
amount of sediment present
• Using a secchi disk (right top) – this
is lowered into the water until the
pattern is no longer visible, and the
depth noted
Sedimentation
• Sedimentation rates are usually
determined by placing sediment
traps in the survey area
Technology: Remote sensing
• Remote sensing utilises satellite
photographs of the area under
survey
• Scientists ground-truth the
images by visiting and fixing the
position of different habitat types
• Software can then match all
similar habitat types on the
satellite image (by colour)
• Therefore the area coverage and
exact location can be identified by
the map alone
Pollution source??
Technology: GIS in marine monitoring
GIS can help us
identify candidate
MPA sites
Questions?