UQx TROPIC101x 7.2.2 Methodologies for Fish and Mobile Organisms
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UQx TROPIC101x 7.2.2 Methodologies for Fish and Mobile Organisms

Welcome back. Fish and other mobile organisms
can be measured using belt transects like those that have been described already. However,
those methodologies do come with a couple of problems and limitations. The first is
that the presence of divers swimming along a reef crest can cause fish to hide or
disappear from the transect leading to much lower estimates of fish abundance and diversity
then there actually may have been. The second problem is that mobile organisms like fish
may behave differently at different times of the day. In this case, differences may
arise in the number of fish observed, simply because of the time of day or night when the
measurements were made, and of course you’ve only got to look at our parrotfish to realise
that they’re very visible in transects by day but of course hiding away inside the
reef by night time. And you would get a very different impression about parrotfish numbers
if you were to measure them in the night time versus the day. One way around this problem is to
deploy unobtrusive video cameras. These can be set up by a diver who can then leave the
area, to pick up the cameras at a later date, and the video records can then be reviewed later
on. You can count fish, you can estimate the size and abundance of those fish, as well
as the frequency of important behaviours such as feeding and grazing. And we recently deployed
this type of video monitoring on deep mesophotic reefs where it’s relly hard to stay down for
very long, to estimate grazing rates and that’s what you’re seeing here in this little piece of video.
You can also use video cameras to do presence and absence studies by actually putting out
food or bait and seeing who comes to the camera when the diver isnt there. Well, let’s now
move onto a brief overview of other methods that one might use to study tropical coastal
ecosystems in the field. In trying to understand how healthy reef system might be, many researchers
have developed physiological instruments which allow them to understand the health of tropical
marine ecosystems and organisms. And in this photograph, I’m using an instrument called a pulsed amplitude
modulated fluorometer, to essentially investigate in the field on a reef, the health of photo-systems
within the symbionts of corals. Now, while this is a complicated instrument, it allows us to get
another layer of information about the state or condition of tropical coastal ecosystems.
Researchers may also take measurements of key chemical and physical variables such as
temperature, chlorophyll, the amount of sediment in the water column, isotopic content, water
clarity, toxins and many other variables in order to understand how an ecosystem works
and whether or not it’s under stress or not. Field measurements may also involve manipulative
experiments. This is a photograph taken during an experiment in which we exposed parts of
the Heron Island reef to ocean acidification. While a challenging experiment, this study
was able to show the sensitivity of corals and other organisms to ocean acidification
under field conditions. This was really one of the first studies of its kind done on a living
coral reef, all the other studies on ocean acidification having been done in the artificial
setting of laboratories and aquaria. As you have already heard, satellites are providing
important information on the distribution and abundance of tropical coastal ecosystems.
I put this photograph here to remind us of the power of relating field measurements,
like the ones described here, to satellite and other large-scale measurements. And these
types of measurements are enabling modern science to understand tropical coastal ecosystems
at scales which are truly global. And in an age of unprecedented anthropogenic-driven
climate change, the importance of these measurements can not be overstated. Attempt the following
quiz, to check your understanding of the different methodologies and approaches that scientists
use to study reefs under field conditions.

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