‘Hide or Get Eaten,’ Urine Chemicals Tell Mud Crabs

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‘Hide or Get Eaten,’ Urine Chemicals Tell Mud Crabs

January 8, 2018
• Atlanta, GA

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Biology professor Marc Weissburg and his students study how aquatic animals use waterborne chemical ques to gather information and affect the community in which they live. Credit: Georgia Tech / Drew Schneider / David Terraso

Psssst, mud crabs, time to hide because blue crabs are coming to eat you! That’s the warning the prey get from the predators’ urine when it spikes with high concentrations of two chemicals, which researchers have identified in a new study.

Beyond decoding crab-eat-crab alarm triggers, pinpointing these compounds for the first time opens new doors to understanding how chemicals invisibly regulate marine wildlife. Insights from the study by researchers at the Georgia Institute of Technology could someday contribute to better management of crab and oyster fisheries, and help specify which pollutants upset them.

In coastal marshes, these urinary alarm chemicals, trigonelline and homarine, help to regulate the ecological balance of who eats how many of whom — and not just crabs.

Blue crabs, which are about hand-sized and are tough and strong, eat mud crabs, which are about the size of a silver dollar, and thin-shelled. Mud crabs, on the other hand, eat a lot of oysters, but when blue crabs are going after mud crabs, the mud crabs hide and stay still, so far fewer oysters get eaten than usual.

Humans are part of the food chain, too, eating oysters as well as blue crabs that boil up a bright orange. The blue refers to the color of markings on their appendages before they’re cooked. Thus, the blue crab urinary chemicals influence seafood availability for people, as well.

Predator pee-pee secrets

The fact that blue crab urine scares mud crabs was already known. Mud crabs duck and cover when exposed to samples taken …

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