[Coral-List] Parrotfish loss drives reef decline

Risk, Michael riskmj at mcmaster.ca
Wed Feb 15 10:23:25 EST 2017

   Good day..

   I  hesitate  to weigh in here, but I thought I would offer some random

   The Kramer et al. paper is a very nice piece of work, using up-to-date
   techniques  (some  of  which  are beyond my limited comprehension). My
   compliments to the authors.

   None of us should be surprised by verification of the importance of grazing
   in reef systems. Personally, I think that ever since Stephenson and Searles,
   Odum and Odum, Gerry Bakus and Kaneohe Bay, the vast majority of coral reef
   research has simply been fine-tuning what we already know.

   There are some aspects of the paper that are worth considering further.
   First of all, few people in this world have looked at more well core than
   have Gene, and he notes that abundance estimates from teeth must be taken
   with  a grain of sand (forgive me). I note that cores were taken by "a
   combination  of  push-coring  and vibra-coring", which produces large,
   relatively  undisturbed  samples  but  means that you cannot core reef
   framework. Authors are to be commended on their good dating techniques (age
   reversals can be used as a proxy for storm transport, which might have been
   worth noting), and one of their three sites records information of the time
   scale of most interest to us: post-1900 (but there the resolution tails off
   a bit).

   This new (to me) CCM technique for teasing out causality seems to be a
   powerful tool, but I note it works if you only consider two variables: as in
   this  case.  Of  course, nutrient proxies would have been difficult to
   obtain-but nonetheless possible.

   Personally, I am not surprised at the lack of correlation with Diadema. If
   we look closely at Gardner et al., we see that the precipitous decline in
   Caribbean reefs began prior to 1960. The dieoff in populations of Diadema is
   in no way reflected in that decline-the line continues its sad progress
   without a blip.

   My concern here is that there may be a tendency to apply these results to
   rehabilitation efforts, and concentrate on bringing back the fish. It is my
   impression that people with a mostly biological focus tend to believe that
   reefs will recover if the grazers come back, whereas those with a more
   varied background in chemistry and geology take a more nuanced approach.

   As  far as I know, there is only one example from the Caribbean of the
   response to an increase in water quality. No one should be surprised to
   learn that the reef came back. Equally, no one should believe the reefs will
   come back if only the grazers come back.


   Risk, Michael
   [1]riskmj at mcmaster.ca


   1. mailto:riskmj at mcmaster.ca

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