Consider this: You or a neighbor are having some construction done. When the construction starts, the noise seems almost unbearable -- you jump every time a nail gun goes off, and cringe whenever the saws cut into a piece of wood, or worse, tile. But after awhile, you start to get used to it. The construction then becomes simply annoying, and maybe even mildly annoying. You stop paying much attention, or at least, you stop reacting to it as much.
That's kind of what ship noise does to crabs. Only when crabs are annoyed by the noise, they stop eating. And when they stop reacting to the frightening noise, they get eaten. Take away an animal's reactivity to noises that alert them to danger and you have lunch.
Science Daily reports on a study published in the journal Animal Behaviour conducted by a team from the Universities of Exeter and Bristol. The team found that the noise from passing ships not only disrupted feeding among shore crabs in the UK, but that the crabs took longer to retreat to shelter when threatened, and they lost their "play dead" behavior.
It seems they are both distracted from eating by paying attention to noise, and take longer than they should in trying to figure out if a noise is from an immediate threat or not. This means they have to spend more time trying to feed, which means more time exposed to predators, coupled with worsening reactions to the threat of predation.
Dr Steve Simpson from Biosciences at the University of Exeter said: "We have already found that ship noise raises the metabolic rate and energetic needs of crabs. If coupled with reduced foraging and worsened responses to predators, this cocktail of impacts may negatively affect growth, fitness, survival and, ultimately, harvested populations and whole ecosystems."