Joined up thinking
So, [almost] live from PlenaryWatch this afternoon, and we’re here to see what Bob Cowen has to say about “population connectivity in coral reef systems”.
Connectivity research has increased dramatically of late – over 60 oral and 80 poster presentations are being given here alone. But what’s it all about?
For most marine organisms, we’re talking about larval stages – the grown-ups tend to stay at home. Population connectivity is the main driver of population and community dynamics. Exchange of DNA between areas affects the degree of genetic isolation between populations. Exotic species spread more easily through well-connected areas, as do diseases. Connectivity is a Big Deal.
Bob talks for a while about how the level of connectivity affects how well connected areas are…
Larval supply is driven by egg production, larval avoidance of things that want to eat them, movements – either through swimming or drifting, or both – and the availability of suitable habitat in which to settle.
The scientific understanding of connectivity has to feed into the management side of things to be any use. Bob’s going to concentrate on the sciencey bit, though.
From an evolutionary perspective, he points out, only a few individuals need to be swapped around per generation. But from an ecological point of view, it might be necessary to be replacing a large portion of the population every generation (if, say, it’s under serious fishing pressure). Those are very different things.
Oooh! Virtual larvae! Off they go, swimming through the silicon sea in Bob’s model of the world. Of 10000 larvae, only 28 are left after 30 days! And most of them are nowhere near suitable habitat in which to settle. Life is indeed miraculous, dear reader. Thank goodness it was all made up in a computer.
Ocean currents are really complicated. Bob puts up a batch of slides showing just how unpredictable they are. Although there are general trends there is a ton of variation, making it difficult to understand exactly how connected areas really are. The images really are impressive. They show how even the most complicated models of current patterns are simplifying the message. In reality things are a lot swirlier than that.
The complexity of these oceanic currents doesn’t bode well for the larvae of the future. Survivorship depends on larval condition, which in turn is affected by things like food availability. Climate change impacts could easily affect the condition of larvae, making it less likely they survive even if they do make it as far as settling somewhere. You’ve got to pity those little fellas, cast adrift at such a young age. But then life’s tough for us all.
Science over, we’re talking management and conservation. From that perspective, models of larval dispersal are important because they can help make clear whether the “problem” (of providing sufficiently well-connected fragments of habitat) is a national or an international one. Many of the areas most affected are island nations, with accompanying social and political issues. At least when connectivity is constrained to a single nation’s coastline there’s half a chance people will work together to do something about it.
Oops, spoke too soon. More science. But this is really cool! Meet the In Situ Icythological Image Scanner. It’s like a… photocopier for fish! Here’s Bob explaining it after the talk…
To sum up, Bob tells us that the ocean is not “average”. In other words, all those charts we’ve been looking at for years and thinking they told us something, don’t. Second, most larvae have a remarkable ability to get where they want to. Third, ecologically relevant dispersal distances are surprisingly small, in the order of tens to hundreds of kilometres. That’s actually a good thing from a management perspective. Finally, there are promising tools being developed to resolve the “larval black box”. We’ve got to know exactly what species are swirling around in those complicated ocean currents.
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