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Do native predators control marine invaders?

December 03, 2012

Do native predators control marine invaders?

With thousands of ships crisscrossing the Panama Canal every year, it is fair to assume the Pacific and Atlantic gateways are exposed to a similar suite of the invasive stowaways

With thousands of ships crisscrossing the Panama Canal every year, it is fair to assume the Pacific and Atlantic gateways are exposed to a similar suite of the invasive stowaways. Yet the composition of introduced species found in the waters on either side of the canal is quite different.

When STRI staff scientist Mark Torchin and his team pull experimental PVC plates from the sea around ports in Panama's Caribbean, they teem with a spongy jumble of colorful marine invertebrates. When they do the same on the Pacific side of the Panama Canal, the plate is comparatively empty – unless it has a cage around it.

Predators likely make the difference. The Pacific's larger fish and crabs quickly finish off many sedentary organisms as soon as they reach snack size. Similar predators are less common in the Caribbean, allowing sessile marine invertebrates to collect en masse. Many of these meal items are invasive species that piggybacked global marine trade to Panamanian waters.

In spite of predator pressure – which is believed to limit the spread of invasive species, especially in the biologically diverse tropics – the Pacific side of the canal has a greater number of invaders than the Atlantic, if species composition on the plates is an indicator. Carmen Schlöder, a STRI research assistant, explains one theory Mark's lab hopes to test soon: “The Pacific has fewer native species than the Atlantic, which could make communities more vulnerable to introductions,” she says. “The more species you have, the less ‘space' is open for new things.”

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