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Article: Follow That Gene! An Interview with Stephen Palumbi

Stanford University-based Stephen Palumbi contributes to the Bahamas Biocomplexity Project by studying the genetic relationships in marine life populations of The Bahamas. Palumbi shares what he knows about corals, conchs, and their spawn…and why genetics matters in marine reserves.


Stanford University marine ecologist Steve Palumbi

What does it mean to study the genetics of a species?

Imagine you’re a conch, and you’re in the Exuma Cays Land and Sea Park. And you’re doing great. You have some babies, and these larvae waft out of the park and into nearby waters. We’re identifying unique genes in conch in the Exumas, then trying to understand how wide those genes spread. The scale of how far genetically related populations spread is the basic data set. We’re also studying coral, spiny lobster, and bonefish this way.

So you’re trailing the larvae?

No, larvae are too small to follow individually. So we analyze the DNA from adults sampled in different areas. This gives us an average view of what the population is doing as a whole. We have to infer what the larvae must be doing from the genetic patterns.

Do you need to take an entire conch to sample its DNA?

We just biopsy the conch, but it turns out this procedure is a fairly brutal affair. The conch are very strong and pull back into their shell no matter what we do to stop them.

But they survive?

Oh, yeah. With a little convincing a conch will come out of its shell enough to biopsy. But once they’re out you have to grab a small piece of their mantle [body] very quickly. We use a surgical instrument we nicknamed Mr. Pinchy.

What genetic geographical patterns are you seeing from your samples?

The patterns for one species can be very different for another depending on their life histories. For example, staghorn corals spawn very small larvae once or twice a year in the summer. The larvae only spend a week in the water before they land someplace.

Conchs, however, spawn over periods of months. The larvae hatch out from egg masses laid all over the reef. They feed in the water column for a little longer than coral larvae do. They settle in areas that require the adults to be around, and they grow up quite quickly.

These two reproductive methods result in very different genetic maps. If you go from one side of a big island to other, the conch genetics barely change. But for coral, the gene pool is very different on either side of the same island.

So coral populations stay local, but conch disperse far and wide?

Well, the conch larvae must be spending more time where the water is moving around a lot. Whereas the coral larvae, even though they’re in the water less than a week, must either have mechanism to be retained and not be washed out to sea. Or if they are washed out to sea, they must not have a way of getting back.


Trailing "Larvae" Via Computer

Does larval movement depend entirely on ocean currents?

Not entirely. Another team in the Bahamas Biocomplexity Project is building computer-based models about how particles flow along currents around the Caribbean. Suppose each of little particles is a gene. When genes move from one place to another that’s called gene flow. Theoretically our team’s genetic data allows us to estimate gene flow.

The idea is to generate both sets of data—a genetic map and an ocean current map—and compare them. This will tell you how much the larvae are depending on currents rather than their own locomotion to flow.

How does knowing how populations disperse relate to designing marine parks?

It gives us an idea of the scale over which we need to add new parks in an area. Coral reefs are damaged all over the place. We’re curious how close a healthy coral reef has to be to a damaged one in order to reseed it.

Or say you’re that conch in the Exumas park. If all your larvae are going to land someplace where they’re going to be immediately caught as soon as they’re big enough, then genetically speaking, the Exumas conch are just stuck there. But if some of your larvae land in another protected area, then in fact those protected places are connected. So the idea is to not just build a marine protected system that is nice to look at but also is likely to have populations that persist.

Related Links

View short documentaries created by Palumbi on coral reefs, marine parks, and undersea life.

   The Palumbi Lab at Stanford

   Stephen Palumbi home page

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