Crustaceans avoid noisy reefs

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Nobody likes noisy neighbours, and crustaceans are not an exception to this rule, according to research published in a recent issue of the online journal PLoS ONE.

Coral reefs are incredibly noisy places, and the study by Stephen Simpson and coauthors have found that many crustaceans are able to detect and avoid reef noise.

Conducting their experiment in the waters of the Great Barrier Reef lagoon, the authors sampled a broad suite of tropical crustaceans with a range of life-history strategies for 34 nights utilising a pair of light traps.  

One of the light traps was randomly allocated a sound system that played back a 4-minute recording of reef noise at a continuous loop through underwater speakers, while the other was set up with a dummy rig.  

The numbers and composition of the crustaceans caught in each trap were then analysed, with the authors also randomly-selected fish caught in the trap to ensure that the composition of the crustacean catch would not be skewed by predation.

After counting as many as 691,000 crustaceans caught in the traps, the authors found that larval stages of crustaceans that inhabit reefs as adults (eg. crabs) were attracted to the reef noise and found in significantly greater numbers in the trap with the sound system.  

Conversely, pelagic crustaceans (those that remain in the water column throughout their lives) and nocturnally emergent crustaceans (those that ascend into the water column at night, but spend the day hidden in soft benthic sediment) were repelled by the reef noise and found in significantly smaller numbers in the trap with the sound system. These included groups such as amphipods, which normally avoid reefs because of the higher density of predators there.

The results of the study indicate that crustaceans are able to detect sounds (although the mechanism for this is still poorly known), and are able to use these acoustic cues to either avoid or move towards coral reefs (depending on their life history).  

Lead author Stephen Simpson said: "The combination of clicks, pops, chirps and scrapes produced by resident fish, snapping shrimp, lobsters and urchins can be detected with our hydrophones from many kilometres away.  

"Our research has already found that reef noise is used by the larvae of fish and even corals to locate and select habitat after their early development in the open ocean, but using noise to avoid reefs, that is a first."

According to coauthor Andrew Radford: "This highlights just how damaging the impacts of human noise pollution may be for so many different creatures.  Chronic noise from shipping, drilling and mining may mask crucial natural sounds, causing animals to make poor or even fatal decisions, which in turn will threaten vital fisheries and tourism resources."

For more information, see the paper: Simpson SD, AN Radford, EJ Tickle, MG Meekan and AG Jeffs (2011) Adaptive avoidance of reef noise. PLoS ONE 6, e16625. DOI:10.1371/journal.pone.0016625