[Coral-List] Parrotfish loss drives reef decline

[David Weinstein]

This is certainly an interesting conversation. It made me think of another
paper someone posted last year that might be interesting to think about as we
debate the current study.

Suchley A, McField MD, Alvarez-Filip L. (2016) Rapidly increasing macroalgal
cover not related to herbivorous fishes on Mesoamerican reefs. PeerJ 4:e2084

https://doi.org/10.7717/peerj.2084


---Ph.D., Coral Reef Geologyhttp://www.rsmas.miami.edu/users/dweinstein/







On Wed, Feb 15, 2017 10:23 AM, Risk, Michael riskmj at mcmaster.ca  wrote:



  Good day..




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

  thoughts.




  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.




  Mike




  Risk, Michael

  [1]riskmj at mcmaster.ca




References




  1. mailto:riskmj at mcmaster.ca

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