[Coral-List] Parrotfish loss drives reef decline

Katie Cramer katie.cramer at gmail.com
Mon Feb 13 15:13:12 EST 2017

Hello Gene,

Thank you for your interest in our study. You are indeed correct that it
does take a good eye (and a good microscope) to detect fish teeth in reef
sediment cores. Although very abundant, the vast majority of parrotfish
oral and pharyngeal teeth were less than 0.25 mm. We only found a few
multi-tooth beak fragments - it seems that the beaks readily disarticulate
into individual tiny teeth once deposited in the sediment.

One novel aspect of our study was that it directly resolved the cause and
effect relationship between reef growth and parrotfish abundance.  We used
Convergent Cross Mapping analyses (
https://en.wikipedia.org/wiki/Convergent_cross_mapping) that allowed us to
go beyond simple correlation to determine that parrotfish abundance
positively drove reef accretion over the past ~3,000 years while accretion
did not have any effect on parrotfish abundance. Other "natural" changes to
the reef ecosystem, such as changes to reef geomorphology, could also have
played a role in declining accretion, but parrotfish loss was definitely a

Finally, archaeological and historical data show that indigenous people
were fishing reefs off the Caribbean coast of Panama 500-1000 years ago. If
you are interested, please see the following papers:

Cramer, K. L. (2013). History of human occupation and environmental change
in western and central Caribbean Panama. *Bulletin of Marine Science*, *89*(4),

Wake, T. A., Doughty, D. R., & Kay, M. (2013). Archaeological
investigations provide late Holocene baseline ecological data for Bocas del
Toro, Panama. *Bulletin of Marine Science*, *89*(4), 1015-1035.

All the best,

Message: 5
Date: Fri, 10 Feb 2017 10:55:42 -0500
From: Eugene Shinn <eugeneshinn at mail.usf.edu>
Subject: [Coral-List] Parrotfish loss drives reef decline
To: coral-list at coral.aoml.noaa.gov
Message-ID: <a834b0c7-6752-1975-6f50-61b117c606b6 at mail.usf.edu>
Content-Type: text/plain; charset=utf-8; format=flowed

One might wonder if the indigenous people of Panama had fishhooks
1000-500 years ago? And, were they able to affect parrotfish abundance
enough to influence coral growth?Of all the many reef cores  drilled
during the past few decades I can?t recall seeing Parrotfish
teeth/beaks. It would take a good eye especially since cores recovered
using these devices are biased toward larger corals. Most uncemented
reef sand that could contain teeth and urchin spines is flushed out and
lost during coring. Even if the article in Nature, ?Parrotfish loss
drives reef decline? is correctly interpreted one has to wonder if the
conclusion is a ?chicken-or-egg-which-came- first issue?? Cores from
Florida reefs show they have suffered periods of non-growth during the
Holocene and in fact cores and seismic profiling show long strips of the
Florida reef tract where corals did not create a coral reef during the
past 6,000 years. With all the sea fans, sea whips, sponges, and
occasional large head corals that populate these non-reef areas it is
easy for the average diver to think they are swimming over true coral
reefs. In the early days of diving I certainly made that mistake.
Whether periods of non-growth, and its causes in the past were the same
as the non-growth we are seeing today is problematic. People in Florida,
unlike citizens of Pacific islands, do not catch or legally eat
Parrotfish. In Tahiti parrotfish are often the most expensive fish on
the restaurant menu. Because we don?t eat them we still have an
abundance of Parrotfish and Blue Tangs that munch the abundance of algae
growing on our mostly dead corals. There is also no competition from
algae eating /Diadema/, which disappeared from Florida reefs (in fact
Caribbean wide) in 1983.

By watching and listening  keys divers can always see and hear the
munching of Parrot fish taking bites from dead coral to get at the
attached algae. I suspect there are more Parrots feeding on our dead
reefs than on live reefs because they do not munch on live coral. On the
Florida reef tract one simply cannot find dead corals that lack
distinctive crisscrossing beak and tooth marks. Our dead reef areas are
literally being chewed away and defecated as reef sand.Any coral polyps
that might recruit to these dead coral surfaces will likely be swallowed
by roving munching bands of Parrotfish and gangs of Blue Tangs. One
might wonder that if these coral munchers were removed would the growing
corals come back? Of course something else killed them in the first
place and that something needs to be solved. It is highly doubtful if
reef cores could be used to determine which came first, death of corals
or Parrotfish removal. Gene


Katie Cramer
Postdoctoral Scholar
Scripps Institution of Oceanography, UCSD

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