[Coral-List] Predictive modelling of coral distribution

William Allison beliamall at dhivehinet.net.mv
Thu Mar 4 03:51:42 EST 2004

Hi Louis,
I wonder if this approach drawn from ground-truthing aerial surveys might
work for your second question, at least for current survey data and if you
have the resources:
1. Make your predictions to fill in the gaps based on the criteria you think
2. Run additional surveys in different sorts of areas that you filled in by
3. Analyse these ground-truth surveys to determine how well your predictions
matched reality.
4. Use these data to calculate probabilities for all predicted areas.
(e.g., estimated 60% coral cover, probability 0.7 etc).

Perhaps if you have redundant surveys and can devise some procedures to
avoid bias you can get away without doing additional surveys.

Of several key references only one comes to mind at the moment:
Sheppard, CRC et al., 1995. Aquatic Conservation: Marine and Freshwater
Systems, 5 (277-298).


William Allison
Rangas, Violet Magu

email: beliamall at dhivehinet.net.mv
On 04/03/03 11:44, "Louis Celliers" <louis at ori.org.za> wrote:

> Greetings, coral listers
> South African coral communities are considered to be high-latitude
> assemblages growing exclusively on submerged quaternary sandstone reefs at
> the limit of coral distribution on the coast of Africa (27deg Lat).  Reefs
> are conveniently grouped in "reef complexes" (North. Central and Southern),
> all within a 150km stretch of the exposed coastline of Maputaland (long-axis
> from N-S).  Reef areas vary between 6ha to as little as 0.1ha.  Total cover
> ranges between 10 and 90 % with the majority of communities (35-55 % total
> coral cover) being either soft coral dominated or mixed soft/hard ("typical"
> WIO coral community, ~110 hard coral species ).  We have been surveying
> these reefs for the last 5 years and we have been using primarily digital
> video/still cameras to collect coral data to generating cover and
> composition (i.e. mainly pattern).  I am comfortable with the sampling
> method  (point intercept counts from high-res digital photography) but my
> question relates to sampling design and data extraction and interpretation.
> The results from our surveys are thus a number of sampling points spread out
> across the reef in what we calculate to be a representative sampling design.
> I apologise if my story is a bit long-winded but the background is
> important:  My question/issues are thus:
> 1)   We have created a grid overlay each reef and I need to populate the
> grid (each individual grid) with species composition, community type,
> susceptibility indices etc and I have intuitively chosen a grid size of
> 100mx100m.  The intuition part of it is obviously going to be problematic
> once this data has to be published.  What would be the rationale for
> selecting a grid size.  I have been toying with the idea of using mean
> longitudinal distance (E-W; mainly changes in depth, also traditional coral
> zones) between sampling points as measure of resolution.  It is obvious from
> the distribution of our sampling points that we favour sampled across the
> reef (E-W) in "groups" from N to S; and it is clear that we interpret and
> make coral community similarity assumptions along bathy lines (N-S). It is
> then possible to calculate the vertical resolution (E-W) of our data and use
> that as a justification for grid size.
> 2) Which brings me to my second point.  Obviously we have to fill the "gaps"
> and develop some sort of a predictive model to generate and justify assiging
> non-data blocks with predictive data because you can't show a manager a reef
> area with only 30 grids populated with data.  Again I am comfortable with
> our sample design but the rationale for linking between sampling points
> remain too subjective (mainly based on bathymetry).  Can anyone possible
> contribute any good references or experiences for
> populating/calculating/modelling the gaps, assiging confidence to grids etc.
> Thanks for actually reading this!
> Louis
> ********************************************************
> Dr Louis Celliers
> Senior Scientist
> Coral Reef Programme
> Oceanographic Research Institute - Durban
> Telephone: +27-31-3373536
> Facsimile: +27-31-3372132
> *********************************************************
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