[Coral-List] resilience is real, we can make a difference

Douglas Fenner dfenner at blueskynet.as
Tue Mar 7 03:23:33 EST 2006

I have been agreeing with most all the thoughts people have been expressing.  The comment of Martin Moe that we need herbivores on our reefs seems particularly apt.  He says "think Diadema."  I say, "think herbivorous fish, too!"  Cozumel, Mexico, had the same dieoff of Diadema the rest of the Caribbean had.  And yet it had no algae bloom.  Why?  Its reef track was all protected, and has abundant fish, including herbivorous fish.  Jamaica had little macroalgae when it had no herbivorous fish left, but still had Diadema.  Either one can do the job, both is no doubt better.  Loose them both and kiss your reef goodby with the next major disturbance.

     I recently had the reality of reef resiliance demonstrated to me.  I visited SW Madagascar.  Most of the reefs where I was had about 95-99% (my guess) of their corals killed by mass bleaching in 1998 and 2000 I was told.  In 2005 when I saw them, they were algae beds with no signs of recovery.  Contrast that with some reefs on the Great Barrier Reef that 5 years after destruction by Crown of Thorns (COTS) or hurricane, had very high coral cover.  In Madagascar, a village on the beach lives almost entirely by fishing, the water is dotted with outrigger canoes every day fishing.  The village has pit toilets, and there are also resorts adding to nutrients.  Few fish on the reefs, probably lots of nutrients.  Enter a major disturbance, results in phase shift to algae and no recovery.  Contrast that to American Samoa where I live and work.  The reefs here are dominated by coralline algae, with corals second.  The two biggest fish groups by biomass are surgeons and parrotfish, both of which are plentiful.  Macroalgae is nearly non-existant.  COTS ate nearly all the corals in the late 70's, there have been several hurricanes (nasty ones in 1990, 1991), mass bleachings in 1994, 2002, 2003.  Chuck Birkeland has been monitoring here for over 20 years, and he says that the disturbances kill coral, but it recovers, time after time.  Resilience to major disturbances is real, and if you have lots of herbivores you have a much better chance of reef recovery.
     I know there are many complicating details, but maintaining a healthy reef with lots of herbivorous fish, low sediment, low nutrients, can make the difference between reef recovery and a reef staying dead.  Controlling these things isn't easy, but it can make a big difference.   -Doug

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