Noise is good for the reef

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Noisier reefs are healthier reefs, according to a study to be published in a forthcoming issue of the Journal of Experimental Marine Biology and Ecology.

Emma Kennedy and co-authors came to this conclusion while studying 11 reef sites in Panama.
 
The authors took recordings of the ambient noises made by the reef sites during the day, and carried out surveys of the habitat and communities at these sites.  
 
When they compared the results of the acoustic and visual surveys, the authors found a positive correlation between fish density and diversity for sounds below 1KHz frequency and coral and benthic invertebrate density and diversity for sounds above 1KHz frequency.  
 
They also found a positive correlation between coral cover and daytime noise intensity across all reef sites.
 
The results are not surprising, considering the fact that reefs are noisy places, with marine invertebrates, including lobsters, crabs, urchins and squid being major sound producers (eg. the sound made by snapping shrimps often dominate coral reef noise).  
 
Fish vocalisations are also prominent, with many fish such as the aptly named grunts (Haemulidae) and drums and croakers (Scianidae) producing sounds as part of their interactions with conspecifics and other fishes; sounds are also produced as a by-product of movement (eg. rapid changes in swimming speed in large shoals) and feeding (eg. scraping sounds of the fused teeth of parrotfishes on coral).
 
The study also highlights the potential for using passive acoustic recordings to survey and monitor the health of reefs.  
 
According to the authors: "Soundscape analysis offers an inexpensive and efficient non-invasive and non-destructive way to monitor ecological changes over time, and even remotely survey reefs to predict fish abundance and coral diversity" in comparison to more expensive and effort-intensive methods such as remote sensing using satellite images and the use of diver surveys.
 
For more information, see the paper: Kennedy, EV, MW Holdereid, JM Mair, HM Guzman and SD Simpson (2010) Spatial patterns in reef-generated noise relate to habitats and communities: Evidence from a Panamanian case study. Journal of Experimental Marine Biology and Ecology doi:10.1016/j.jembe.2010.08.017