[Coral-List] Reliable coral reef stats

John McManus jmcmanus at rsmas.miami.edu
Thu Sep 19 14:34:33 EDT 2013

A few years ago, we were asked to look into existing coral reef sampling
protocols to determine what is most appropriate as use as a baseline for a
future mitigation concern. We studied every standard we could find from the
standpoint of its utility in identifying and quantifying what ecological
'functions' would be lost over time after the damage (as per federal
regulations, where in these functions are not well-defined -- but we did
what we could in that regard). The answer was: none.

The closest was a methodology in which coral colonies were identified and
measured as part of the sampling, combined with remote sensing bottom
classifications. From this one can obtain rough estimates of potential rates
of recovery from previous rates of recruitment and mortality, and quantify
the recovery spatially. However, aside from the obvious problem in defining
a 'colony' in some circumstances, the approach involved measuring only the
longest dimension. This was fine for the purposes of the original
methodology designers, but for us, it added a systematic error -- comparable
to that of putting transect lines on places with the highest local cover, as
sometimes encountered in other protocols. Still, because the bias is known
and systematic, prior data could still be used with a correction factor,
based either on rationalization or, ultimately, on comparative sampling
(something that would be good for those 'highest cover' surveys). Of course,
we recommended that multiple colony measures be used for mitigation cases. 

One point of this is that there is no 'one size fits all' sampling approach.
If someone needs to identify change in a specific reef, one should match a
sampling unit to the purposes of the study, select an appropriate
statistical design, choose the appropriate number of sample units from which
to obtain data based on an analysis of estimated or pre-sampled local
variance, and try to minimize bias throughout the process. Although some
people use experimental design procedures for this, it is much better to
actually use sampling design principles (see books by Hayek and Buzas,
Thompson, or the old Cochran book, or better, get a statistician to help
early on!).   

Usually, formal statistical design is not practical for sampling across many
reefs (though given the appropriate prior funding commitments it would be
feasible), so we must trade off intensiveness for extensiveness. Every
methodology has pros and cons for this. Reef Check's approach is very
'extensive', gathering less data to lower cost and permit very wide, rapid
sampling. All existing methods have biases one way or another. I think the
worst bias we see in regional and global surveys is that of reef selection
-- we sample primarily convenient, well-known reefs. We have seen specific
efforts to gather information from less-known and distant reefs (including
efforts from Reef Check, AGRRA, NOAA, Cordio, etc.), and so this bias can
increasingly be adjusted for via appropriate data groupings and weightings
-- assuming that all this data are made publicly and easily available .    

I am not associated with Reef Check, but it clearly is the best thing we
currently have in terms of global coverage using a uniform standard. 

However, as global concerns about reef issues increases, there may be new
opportunities to improve sampling protocols. So, I encourage discussion on
how assessments at national, regional and global scales can be improved. So,
please do suggest better ways to obtain this vital information. Critique
without suggestion is not terribly helpful.



John W. McManus, PhD
Director, National Center for Coral Reef Research (NCORE)
Professor, Marine Biology and Fisheries
Coral Reef Ecology and Management Lab (CREM Lab)
Rosenstiel School of Marine and Atmospheric Science (RSMAS)
University of Miami, 4600 Rickenbacker Causeway, Miami, 33149
jmcmanus at rsmas.miami.edu      http://ncore.rsmas.miami.edu/
Phone: 305-421-4814   

"Far better an approximate answer to the right question, which is often
   than an exact answer to the wrong question, which can always be made
     --John Tukey, Statistician, National Medal of Science and IEEE Medal of

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of David Fisk
Sent: Wednesday, September 18, 2013 1:11 PM
To: coral-list at coral.aoml.noaa.gov
Subject: [Coral-List] Reliable coral reef stats

Some time ago a question was asked on Coral List regarding the
appropriateness of Reef Check (RC) for monitoring and I seem to remember
that no real answer to the question was offered by anybody at the time. So
this latest contribution from RC headquarters has offered a chance for me to
give my two cents worth that I should have done the first time. What I would
like to know is whether there is anybody else out there in Coral-List land
who like myself, feels a little uncomfortable whenever we are given the hard
sell from Reef Check, particularly in its effort to legitimise its
scientific credential claims with what is and will always be, a simple
community awareness raising tool. Reef Check was developed solely as a
community awareness tool and has been included in the GCRMN list of
protocols under that category, and is widely understood to be the least
scientifically robust method for most ecological questions. And yet over the
years the assertion of its scientific rigour and global usefulness to answer
scientific question has grown beyond its initial purpose.

RC's main usefulness lies in getting many observers in the water over a wide
geographical scale, with the possibility of ocean wide or regional scale
phenomenon being recorded, like regional bleaching events which at that
scale, does not actually need scientific rigour to be confident that a broad
scale disturbance event is occurring.

My greatest concern is that the Reef Check juggernaut, principally because
of its well organised format, gets presented to many developing countries as
the basic tool for all reef related issues that a country may be concerned
about. This results in the collection of data that are entirely useless for
the real local issues that they may be faced with. The monitoring data may
be of some use for regional assessments but I remain sceptical and uneasy
about the extremely limited resources of these poor countries being used for
the good of regional/global assessments only. The reason I say this is that
the pro forma list of indicators species and sample sizes and replicates
required by RC are rarely useful for smaller scale questions like Pacific
Island fisheries departments (for example).
Yet many such organisations are led to believe that Reef Check is all they
need to monitor their fisheries or to answer specific disturbance issues, or
provide an accurate reef status, which it clearly cannot do.

Furthermore, the interpretation of data from a protocol like RC should be
treated with caution for a very wide range of reef organisms listed as
health indicators by RC. A good example is the use of humpheaded parrot fish
and maori wrass as 'health indicators' in the Pacific. Both species have
very large home ranges that probably extend to a kilometer or more of reef
tract, so when very small belt transects are used (RC suggests 20m x 5m belt
transect replicates), any observation can only be interpreted as the species
being being present, and nothing can be said about their true abundance or
density as the sampling is inappropriate with respect to the target species'
normal home range. Most importantly, the absence of such species in RC
survey records does not mean they are not present, just that the sampling
regime is inadequate and did not cover the likelihood of them being

Another significant issue is the choice of sites for RC as to their
'representativeness' with respect to the aims of a project. RC predominantly
utilises volunteers and diver/resort type people to establish monitoring
sites and to gather data, but from my experience, the choice of sites are
highly biased towards habitats and sites that are appealing to such
volunteers such as high coral cover sites, drop offs, or sites where tourism
operators can safely moor boats.

In summary, drawing conclusions on the 'health' of large regional reef
systems and the management of coastal fisheries using RC data is obviously
wrong for any inappropriately sampled species groups and in most cases the
RC protocol does not address the real issues of many countries.

Don't get me wrong, I believe there is a use for RC but I think it is not in
the areas that are becoming too frequently claimed by RC.

Now, where is my crash helmet - I suspect I may need it.  Cheers Dave Fisk

> Since 1997, Reef Check has carried out a global monitoring program of
> reefs using a standardized method based on about 30 indicators 
> including living coral and recently killed coral, bleached and 
> diseased coral. Prior to 2005, Reef Check teams were trained and led 
> by Masters or PhD level scientists who were responsible for field 
> level Q & A. Since 2005, all
> Check data has been collected by individuals who have been through a
> training program, tested and certified to collect data.  In fact about 
> 75% of the data has always been collected by research scientists 
> because Reef Check methods have been adopted by many countries and 
> research institutes as part of their core monitoring program. 
> Independent researchers such as
> Bruno et al., have used the database for local and regional meta analyses.
> The database is available to any researcher. Our WRAS online coral 
> reef database has been taken offline to transition it from a GIS to a 
> Google Earth platform, and to merge it with our California NED online 
> rocky reef database. http://ned.reefcheck.org/ An analysis of the 
> 15-year coral reef dataset is due out in 2014. For a list of peer 
> reviewed and other
> publications based on or related to Reef Check data please see:
> http://reefcheck.org/about_RC_Reef/Publications.php
> Reef Check offers regular training programs throughout the world using 
> our local coordinators. If you think it is important to track coral 
> reefs during the next 20 years of global warming, please contact 
> rcinfo at reefcheck.orgto arrange a training or if you would like to help 
> coordinate surveys in a country where we do not have a coordinator.
> I am noticing two problems when researchers try to compare baselines 
> now with pre-1980s data:
> 1. there is a shifting baseline in new cohorts of coral reef 
> researchers who have a hard time understanding what reefs actually 
> were like 40 years ago, but typically have not read the old 
> descriptive literature from pre-1970s such as Saville-Kent that 
> provide exceedingly detailed descriptions of
> the shallow reefs were like; 2. a problem with meta-analyses that do 
> not take into account the fact that in 2013, there are no "zero coral
> data from former reefs or zones of reefs that are no longer reefs 
> because they experienced 100% die off and so researchers no longer monitor
> Some former reef zones that were populated by Acropora palmata can 
> still
> seen, as the dead skeletons are still in place, but those formerly 
> populated by the more fragile A.
> cervicornis are often simply gone. This means that the current 
> regional
> global coral cover estimates are probably underestimating the decline 
> as researchers no longer include reefs that died and have not recovered.
> Gregor Hodgson, PhD
> Executive Director
> Reef Check Foundation
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