Monday, 15 January 2018

'Hide or get eaten,' urine chemicals tell mud crabs

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 the mud crabs, which are about the size of a silver dollar, and thin-shelled. Blue crabs also eat a few oysters, but mud crabs eat a lot more oysters than they do. 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.

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