[Coral-List] Best practice for LIT surveys

[William Allison]

I have tested every survey methods I use for comparability, efficiency and
effectiveness. My general approach resembles that described by Les. For my
line intercept and point transects I use a fiberglass tape anchored as often
as necessary to stabilize it and kept as level and as straight at possible
and with no bends between stakes. I am very careful to accurately re-situate
transect lines when I do repeat surveys and I use a plumb-bob (1 cm diam at
the top and ~6 cm long, tapering to a sharp point). Repeated tests of this
approach show high repeatability for individual colonies and sensitivity to
a change of a few percent for the whole transect. This is is possible
because the line is in the same place each time (not the same general place,
not more or less the same deployment but the same deployment), and parallax,
sighting eye and other perceptual and cognitive biases are largely
controlled. Even with substantial surge results are much more repeatable
than surveys done with the un-aided eye or than surveys done with a chain or
similar method. When the sessile benthos constitutes a mosaic of small
items, the line intercept transect is inherently unsuitable for the task.
For such a benthic situation combined with surge it is not worth the bother
to do a line intercept survey of any sort. Under these circumstances a point
transect with a plumb-bob is provides reasonable results - the plumb-bob is
dropped at a designated point on the line and what is hits is recorded. In
effect the surge adds an element of latteral randomness and it becomes a
point survey along a belt transect.

Bill

On Wed, Dec 31, 2008 at 5:19 AM, David Fisk <davefisk at gmail.com> wrote:

> With all the talk about LIT deployment and practical considerations, seems
> like it might be a good time to add a few more comments into the discussion
> before it disappears off the scene. I am aware of at least 2 MSc theses
> looking at the accuracy and precision of the LIT method. One was done by
> Craig Mundy from James Cook Uni in Townsville and another by a post grad in
> Canada (I am sorry I can't remember the name of the person right now). Both
> did these studies back in the 1980-90's.
>
> Both bascially found problems with the precision of the method, so much so
> that a tape that is strung out for 20m and tied every 5m with plastic
> coated
> wire to stakes hammered into the substrate, still came up with an average
> 20% difference in repeated cover estimates. And this held true for a
> situation where the same recorder read the intercepts for a number of
> repeated times - further more the benthic surface where the tests were done
> had very low relief and there was neglible water movement and therefore
> tape
> movement. So despite its widespread adoption as a monitoring tool, it has
> limitations like all methods that should be kept in mind when interpreting
> the data.
>
> LIT is of course known to be inaccurate in estimating the true number of
> small colonies in a population. All monitoring methods have their pros and
> cons, and personally I find the LIT very time consuming and of limited
> application with the above precision problems and inaccuracies wrt the
> under
> estimation of smaller colonies, not to mention the deployment issues
> already
> discussed. For an approximate estimation of coral cover, there are probably
> better methods available that require less field time and number crunching
> time, but a combination of rapid recording methods that include a permanent
> pictorial record is ideal.
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> http://coral.aoml.noaa.gov/mailman/listinfo/coral-list
>