[Coral-List] Parrotfishes and coral reef health

[Peter Sale]

Kudos to Tim McClanahan, in particular, for quietly reintroducing a touch of realism into this discussion.  Coral reef decline is proceeding around the world, but seems to me to be particularly severe in the Caribbean.  (Perhaps that is because of the relatively small number of primary reef builders in that system, some of which have been savagely hit by disease.)  The decline is caused by many concurrent stressors (Judy Lang's post hit most of them in one sentence).  The relative importance of these stressors varies from place to place, and from time to time.  The long-term trajectory looks very bleak.

I doubt any of you disagree with my first paragraph.  But if we reef scientists, and particularly the reef ecologists amongst us, cannot remember that this is a case of simultaneous, possibly synergistic, stressors acting in different ways on different species when we discuss what is happening, how can we expect other people to comprehend the magnitude of the problem?  To spend lines and lines of text on coral-list debating whether or not parrotfish grazing is to blame (as if one factor will be the leading cause of decline across time and space) cheapens the discussion and reduces any chance of articulating clearly what is needed to gain some improvement.  We can all do better.

And please, let us stop reducing the concept of herbivory, by parrotfishes, sea urchins or anybody else, to a simple binary interaction between the grazer and the macroalgae, with the corals waiting patiently on the outcome.  What utter nonsense.  It's been well documented in numerous marine environments that algae of different species respond differently to grazing pressure.  Most macroalgae escape most of the herbivore guild through growth, so that the suite of herbivores that might keep a bare site free of anything other than a fine algal turf is quite incapable of returning a lush stand of macroalgae to that fine turf state.  Different species of macroalgae are differentially palatable to different species of herbivore, are differentially impacted by pollution, by nutrients, by storms.  I could go on.  Even understanding the algal-herbivore interaction requires much more subtle ecological insights than are evident when all parrotfishes and all algae are considered interchangeable.  If we do not improve the way in which we talk about the loss of living coral on our coral reefs, we diminish the chance of really understanding what is happening, or potentially discovering effective management actions.  We are all capable of elevating the level of discourse.  If the world is destined to lose most of its coral reefs this century, I'd like to think that at minimum, we had at least learned what was happening, and could articulate what would have been needed to prevent that eventual demise.  We cannot learn from our mistakes without understanding clearly what has happened, and the eventual demise of coral reefs, if it does happen, needs to become a teachable moment.

Peter Sale
University of Windsor