'44
Concepts
Population
distribution
Abundance
Habitat
Adaptation
Competition
Niche
Sustainable
yield
Skills
Observing
Collecting and
recording data
Synthesising data
Hypothesising
Attitudes
Appreciation of
natural
environments
Confidence in
making
observations
Interest in methods
of science
2 hr +1 hr • •)
Aim
• To estimate the size and density of the sea-cucumber (holothurian)
population of the reef-top.
• To gain an appreciation of the part sea-cucumbers play in the reef ecosystem.
You will need
•
Reef-walking gear and possibly snorkelling gear
•
Underwater board, waterproof field sheet and pencil
•
Reference material
•
Measuring tape or cord (20 m) (optional)
•
1-metre string, or metre stick
•
Map or air photo of reef
•
Ruler
• Transparent graph paper (optional)
This activity requires about two hours at low tide for fieldwork and about one
hour for follow-up work.
PRECAUTIONS
Avoid
touching eyes after handling sea-cucumbers. Material from these
animals may irritate the eyes.
What to do
Gathering data (field work)
1. Divide into small groups (about four people per group). Each group is to
make a transect at low tide across the reef-top from beach to reef crest,
counting sea-cucumbers.
(a) Each group should select a starting point which is recognisable on a map
or air photo, take a compass bearing to the reef crest and walk along this
bearing.
(b) Use a knotted cord or measuring tape as the transect line, or measure the
transect line using paces.
(c) At sample points every 20 metres along the transect line, count all the sea
cucumbers in a 4-square-metre area (you could conveniently do this by
looking at a 2-square-metre area on either side of the transect line at each
of your sample points). If you can, decide what species the sea-cucumbers
belong to by referring to reference material.
(d) Record the information on the field sheet.
26.
Cucumber count
Analysing data
2. Work out the
average number of sea-cucumbers
(all kinds)
per square metre
on the reef-top.
One way this can be done is to combine the totals from each station on your
transect and divide this by the total number of square metres sampled.
3. Make an estimate of the
total number
of sea-cucumbers on the reef flat and
reef rim.
(a) Use a map or air photo to work out the total area of the reef-top (not
including lagoon, if present). (A grid such as transparent graph paper will
help you do this.)
(b) Use the value obtained in (2) for the average number of individuals per
square metre. Multiply this by the total area of the reef-top (excluding
lagoon).
4. Work out the
relative numbers
of the various species of sea-cucumber. (List
the names of the species in order of abundance. Express the relative
abundance as a ratio.)
FROM PROJECT REEF ED
© Groat Sorrier Root Morino Park Authority
52 -7/
