Lessons in Coral Reef Survival

The complex relationship we see today between fishes and corals developed relatively recently in geological terms – and is a major factor in shielding reef species from extinction, says Professor David Bellwood of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

"Our latest research provides strong evidence for a view that today's coral hotspots are both a refuge for old species and a cradle for new ones," said Peter Cowman, lead author of a recent report. "This is the first real inkling we've had that just protecting a large area of reef may not be enough – you have to protect the right sorts of reef."

Early coral reefs, 300-400 million years ago were much simpler affairs than today's colourful and complex systems, Prof. Bellwood says. The fish were not specialised to live on or among corals – either lacking jaws altogether, or else feeding on detritus on the seabed or preying on one another.

"By 200 million years ago we are starting to see fish with jaws capable of feeding on corals, but the real explosion in reef diversity doesn't occur till about 50 million years ago when we see fishes very like today's specialist coral feeders emerging."

It is the ever-increasing complexity of this relationship between corals and fishes over the last 20 or 30 million years that produces the wondrous diversity of today's reefs, he says. Each has become more critical to the survival of the other as their lives have become more interwoven.

"When people think of coral reefs, they usually think of the beautiful branching corals like staghorn (Acropora) – well the evidence is now fairly clear that Acropora needs certain fish for it to flourish. But, it now appears that this may be a reciprocal relationship with Acropora being important for the evolution and survival of fishes on coral reefs. "

Unfortunately Acropora corals are highly vulnerable to external impacts like Crown-of-Thorns starfish, coral bleaching, climate change and ocean acidification. Their demise will have far reaching effects on the fishes which interact with them, such as damsels, butterfly fish, cardinals and wrasses.

"The study of the past tells us that reefs are all about relationships and, like a family, for them to survive those relationships need to remain strong," Peter Cowman said. 
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