Ship Noise Makes Crabs Cranky
February 27, 2013

Man-Made Noise Makes Marine Crabs Cranky

Brett Smith for - Your Universe Online

Private industry rarely has a stake in conservation, but a new study shows that reducing aquatic noise pollution could provide a financial boost for the fishing industry. A new study published in the journal Biology Letters found that the sounds of ship noise ramp up crab metabolism, potentially resulting in lower yields for commercial crabbers.

Citing growing evidence that shows even a single noise exposure can affect a variety of vertebrates, conservationists are constantly looking to reduce man-made aquatic noise because of the possible negative impacts on underwater animals.

In the study, a team of UK scientists wanted to determine whether marine invertebrates are also affected by anthropogenic noise.

"We used controlled experiments to consider how shore crabs of different sizes respond to both single and repeated exposure to playback of ship noise,” said study co-author Matt Wale, from the University of Bristol's School of Biological Sciences. “Ship noise is the most common source of noise in the aquatic environment."

The researchers found that the crabs´ response to a single ship-noise playback was largely dependent on their size, with heavier crabs tending to show a stronger response than their lighter-weight cousins.

"We found that the metabolic rate of crabs exposed to ship noise was higher than those experiencing ambient harbor noise, and that larger individuals were affected most strongly,” said Andy Radford, a behavioral ecologist at Bristol. “This is the first indication that there might be different responses to noise depending on the size of an individual."

Surprisingly, after repeatedly exposing the clawed crustaceans to ambient noise, the researchers found that the crabs increased their oxygen consumption, a biological process commonly associated with stress. However, repeated exposure to ship noise did not result in a physiological response. The researchers theorized that that crabs exhibited a maximum response at the first exposure to ship noise playback, but they eventually become tolerant to it.

The research team pointed out that their results are especially important since they show that invertebrates are also sensitive to anthropogenic noise. Co-author Steve Simpson from the University of Exeter“¯said his team´s study could have an impact on both fishing areas in the open water and commercial farming operations.

"Since larger crabs are affected more strongly by noise this could have implications for fisheries in noisy areas,” he said. “Also, many crustacean species, particularly prawns, are grown in aquaculture, so if acoustic disturbance has a metabolic cost then operational noise in farms may impact on growth, and quieter farms may be more profitable."

The team also called for more “detailed investigations into the effects of this pervasive global pollutant.”

If anthropogenic noise were to worsen, the negative impacts on invertebrates could be felt all the way up the food chain. For example, horseshoe crabs are not valuable commercially, and many people visit the ocean shore consider them a nuisance.

However, horseshoe crabs play an important role in the coastal food web. Any negative impact on their population would be felt by the crabs´ predators, such as shorebirds and sea turtles. Shorebirds depend on horseshoe crab eggs, which are available only if this species is spawning at high densities.