[Coral-List] Will the reefs die completely??

Douglas Fenner douglasfennertassi at gmail.com
Thu Sep 13 17:53:43 EDT 2012

    There is a new 8 minute video on the web in which Prof. Terry Hughes
says that in the future there will be winners as well as losers as higher
temperatures produces bleaching that kills some corals.  He says Acropora
may be killed quickly, but Porites is tough and will survive.  "if we can
avoid dangerous climate change."  See what you think.


The text is:

It was a major shift in the climate, the end of an ice age twelve thousand
years ago that made the Great Barrier Reef possible. As temperatures
warmed, melting glaciers transformed the continental shelf into a warm,
shallow sea; conditions perfect for an explosion of life.

*Ruben Meerman*
Ironically, it's now predicted that our changing climate could be the
demise of the reef, but I'm on my way to meet a man with a more optimistic

>From up here you really appreciate Nature's handiwork, this maze of
islands, coral caves and almost three thousand individual reefs, stretches
for over two thousand kilometres; an expance so vast it can be seen from
space.In the middle of it all is my destination, Lizard Island. It's a
place Professor Terry Hughes knows well.

*Ruben Meerman*
Hi Terry.

*Prof Terry Hughes*
G'day Ruben. How are you? Welcome to Lizard Island Research Station.

*Ruben Meerman*
Thank you. What a magic day.

*Prof Terry Hughes*
Oh it's beautiful isn't it?

*Ruben Meerman*
Let's get out there.

*Prof Terry Hughes*
Yeah the wind's picking up so the sooner we go the better.

*Ruben Meerman*

Terry recently spearheaded the first large scale investigation into whether
warmer waters really will spell the end for all coral species.

*Prof Terry Hughes*
We had a big wakeup call on the Barrier Reef in 1998 and again in 2002 when
we had huge bleaching events that affected the Barrier Reef along its whole
length and across its whole breadth. So I'm interested in how climate
change and other human impacts on reefs are changing the species
composition of coral reefs.

What we call coral are actually colonies of hundreds to hundreds of
thousands of tiny creatures called polyps. Living in their tissue is
photosynthetic algae called zooxanthellae, which provide corals with
essential nutrients and healthy colour. But when the water becomes too
warm, the zooxanthellae are expelled, leaving the coral bleached.

*Prof Terry Hughes*
That was the first time we'd really seen bleaching at that scale. We were
worried about the long term impact this will have on the reef because the
world is getting warmer and warmer and the frequency and intensity of
bleaching events is, is inevitably going to go up.

Water temperatures increase as you travel up the coast. The hottest
temperature in the north of the reef is a full nine degrees warmer than the
coolest temperature in the south. This gave scientists a unique opportunity.

*Prof Terry Hughes*
We were interested in how the mix of species might change along that huge
thermal gradient and what that might tell us about the flexibility of
corals, how they put themselves together to make an assemblage of species,
how that might change in response to climate change and global warming.

Terry's team surveyed thirty three sites, spanning the entire reef,
identifying over thirty five thousand individual coral colonies. The study
has given us a more detailed understanding of the changes that will take
place as the world's oceans gradually warm.

*Ruben Meerman*
The good news is complete reef wipe outs are unlikely. Coral reefs like
this one will still be here in fifty years but they will be very different.

*Prof Terry Hughes*
The picture that's emerged over more recent studies is that bleaching is
incredibly selective. It's actually acting like a giant filter in that it's
changing the mix of species because some are much more susceptible to
bleaching, others are much more resistant. There are winners and losers if
you like.

All it takes is for water temperatures to rise just one or two degrees
above the seasonal average for several weeks and susceptible species can

*Ruben Meerman*
What sort of coral's this guy?

*Prof Terry Hughes*
This is a branching coral. It's called Acropora.

*Ruben Meerman*
In terms of climate change survivors, how do these fit in?

*Prof Terry Hughes*
These guys generally speaking are among the most susceptible corals to
bleaching. So these things live life in the fast lane. They recruit at a
very high rate, they grow quickly and they die young.
We found a huge flexibility in the mix of species from north to south and
that gives us some optimism that when susceptible species, the losers if
you like, decline, that they won't all decline at the same extent and in
fact we might get some of the winner species actually increasing.

More robust corals can handle the rise of up to four degrees for a month or

*Prof Terry Hughes*
Often, one of the last corals are left on the degraded reef is this
particular species called porites.

*Ruben Meerman*
So these sorts of corals will be the winners in the future if the climate

*Prof Terry Hughes*
These are the toughest corals going.

*Ruben Meerman*

*Prof Terry Hughes*
This thing is two hundred years old at least.

*Ruben Meerman*

*Prof Terry Hughes*
So yes they're withholding, they're standing their ground. They are the
winners in the future.

So while there is a future for the hardier species, it's not such good news
for the fish that depend on the more delicate branching and table corals
for habitat.

*Ruben Meerman*
Once we lose all those really lovely three dimensional corals, what does
that mean for the critters that live on the reef?

*Prof Terry Hughes*
Well there are lots of species that depend on corals for protection from
predators. There's a small number of fish species that actually eat corals.
When corals become scarcer, those species will become less and less
abundant. It's a very dynamic system and climate change is changing the
whole way that reefs function.
I don't agree with statements that the Great Barrier Reef will all be dead
in twenty years time. It will be very different from today's mix of species
but I'm reasonably optimistic that if we can avoid dangerous climate
change, we'll still have a Great Barrier Reef.
 Topics: Environment<http://www.abc.net.au/catalyst/stories/by-topic/ENVIRONMENT.htm>

   - Reporter: Ruben Meerman
   - Producer: Roslyn Lawrence
   - Researcher: Roslyn Lawrence
   - Camera: Brett Ramsay
   David Parer
   - Sound: Paul Castellaro
   - Editor: Andrew Glover
   Toby Trappel

Dept. Marine & Wildlife Resources, American Samoan Government
PO Box 7390
Pago Pago, American Samoa 96799  USA

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