Let Them Eat Shrimp by Kennedy Warne

Author:Kennedy Warne
Language: eng
Format: epub
ISBN: 9781610910248
Publisher: Island Press
Published: 2012-06-19T04:00:00+00:00

We walk on through the Lilliputian mangroves, sometimes sinking to our knees in the slushy sediment. It’s like walking through thick soup. The soil here is the finest peat, formed from billions of roots composting over thousands of years. Candy says the peat is two meters (seven feet) thick—most of it from fine mangrove roots. It accumulates so quickly that mangrove islands such as Twin Cays are rising by a few millimeters a year.

Several saltwater ponds dot the interior of the islands. They are full of upside-down jellyfish and a delicate alga with surely the most beautiful name of any seaweed: mermaid’s wineglass. The “wineglasses” are clusters of fluted green or white cups, about an inch in diameter, borne on long, slender stalks. Nosing around them in the shallow water are chubby fish called checkered puffers.

Candy starts poking among the branches of her bonsai trees, looking for critters. During the course of her research she has found more than a hundred species of arthropod (insects, spiders, crustaceans, and their ilk) associated with the twigs of red mangrove. Included in this pantheon are termites, scorpions, puss moths, roaches, bag worms, mites, spiders, and many more. Thirty-five of them are wood-feeders, and seven are specialist wood-boring beetle and moth larvae that feed exclusively on Rhizophora mangle twigs.

Wood borers function as “ecosystem engineers”—gamechangers whose activities alter the ecological playing field for other creatures. A wood borer, for instance, may drill out the core of a living twig, killing it. When the borer leaves, its exit hole becomes an entranceway for the next species in the chain—perhaps a borer that feeds only on dead wood. Still later, the hollowed-out twig may be occupied by ants, crickets, or even, as Candy discovered, a species of carnivorous ribbon worm that feeds by everting its gut, wrapping it around the prey and swallowing it whole.

Candy has more than just a zoological interest in these creatures. She wants to learn how the nutrient overenrichment of mangroves affects herbivores and upper trophic levels in the food web. “Nutrients are the currency of food webs,” she says. She adds nutrients to experimental plots, then follows how they move through the ecosystem in the same way an auditor follows a money trail. The three major elements she’s interested in (the dollars and cents) are carbon, nitrogen, and phosphorus. She compares the ratios of each element in the mangrove trees in her study plots, and also in the herbivores that eat mangroves.

Candy believes that herbivores have a far greater influence on the structure and function of mangrove ecosystems than they are usually credited with. “They control both the amount and the distribution of forest biomass,” she says. A sprouting mangrove propagule, for instance, may have terrestrial borers burrowing down from the top and marine borers burrowing up from the bottom. From her studies, Candy estimates that as many as 99 percent of red-mangrove propagules are killed by wood borers.

A somewhat larger sphere of influence is held by a type of beetle larva that girdles entire mangrove branches, cutting off the sap flow.

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