How Sound Travels Through Water to Animals
Today's invitee post is presented courtesy of Lauren Freeman, an NRC Postdoctoral Swain at the Naval Enquiry Lab. She studies how humans impact ocean habitats including coral reefs and coastal estuaries.
Rachel Carson's 'Silent Spring' was groundbreaking for the environmental move. Information technology sparked the kickoff major public awareness of the negative effects of industry on ecosystems. An often looked-over aspect of the book, however, is the title. Instead of looking at an ecosystem to determine how healthy it is with our eyes, we can as well mind. Stop and think for a moment of the concluding time you wandered through the wood. We used to inherently know that the woods should exist noisy - crunching leaves and sticks as animals run nearly, birds calling, insects singing and buzzing, etc. To hear nothing is disconcerting, and a very clear bespeak that something is incorrect - danger is coming, or mayhap it has already arrived.
It has taken awhile for technology to take hold of up to this concept, but at that place are at present digital recording devices and signal processing algorithms sophisticated enough to characterize ecosystems through the sounds they make. Such work was kickoff done in the Amazon rainforest. Many other terrestrial studies, most focused on bird songs, followed.
What about under the sea? Jacques Cousteau threw u.s.a. off a little by using the captivating championship 'the Silent Earth' for his famous film and book. Underwater ecosystems are annihilation but silent, although our ears aren't well adjusted to characterize many of these sounds. Put your head underwater near the shore in whatsoever tropical sea and yous will hear an array of pops, crunches, grunts, snaps, scrapes, and more. Many fish communicate with sound (ever wonder why a croaker is called a croaker? That whole family of fish produces deep grunts and pulses with their swim bladders.) Parrotfish scrape off big bites of coral & limestone throughout the day, somewhen depositing pure white sand on the reef after they have digested the edible parts. The myriad of small benthic invertebrates - animals such every bit hermit venereal, sea urchins, lobster, and shrimp - are known to brand noises that range from snapping and clicking to scraping and grunting. All of these noises tin can exist recorded on hydrophones, the same tools that are used to runway the calls of dolphins and whales
Audio travels much more than efficiently and faster through the water. Furthermore, the bounding main surface is an splendid reflector, sending audio coming upwards from the sea back down over again with almost no attenuation. As a event, the shallow water environment is a very repeat-y place. Sounds made by animals tin can reverberate and make for confusing recordings. Think about how difficult it would be to talk to your friend if you were both in a crowd of very talkative people, in an repeat chamber!
Having one hydrophone provides 1 dimension of information - the level of noise at a given time. Using several hydrophones strung together in an assortment, scientists can abolish out the echoes and encounter where the audio comes from - the management and the altitude to the sound source from the array. A new paper in the Periodical of the Acoustical Society of America shows that with a hydrophone array it is possible to not but record the sounds of an underwater ecosystem, just also to triangulate the location of many specific sounds, simultaneously. The end result is a detailed map of the underwater soundscape - a 'map' of sound produced by many unlike animals - in this example, on and inside a coral reef.
This methodology has potentially significant implications for marine ecology. Nearly oceanographers love fieldwork, but the difficulty of accurately surveying the underwater ecosystem past SCUBA diving and directly observing the organisms in the h2o are pregnant. Defined are limited to an hour or then earlier they run short of air. Visual counts don't note the myriad of animals living out of sight inside the reef structure. Benthic ecologists have shown that by taking large chunks of coral dorsum to the lab, preserving all of the living things inside with ethanol, so breaking apart the rock and counting everything inside, well-nigh of the biomass on a coral reef really resides within of the reef structure - completely invisible to SCUBA divers. The sounds from these organisms, however, can transmit through the reef and out into the water.
In improver, the presence of large, loud, bubble-making humans can startle reef inhabitants and send them scurrying out of sight. A hydrophone array, which but listens and makes no dissonance itself, can remain stationary on a reef for days or weeks of time, passively collecting data about the ecosystem without agonizing any of its inhabitants.
References:
Blumstein, D. T., Mennill, D. J., Clemins, P., Girod, L., Yao, K., Patricelli, Grand., ... & Kirschel, A. N. (2011). Audio-visual monitoring in terrestrial environments using microphone arrays: applications, technological considerations and prospectus. Journal of Applied Ecology, 48(3), 758-767.
Freeman, Due south. E., Rohwer, F. L., Gerald, Fifty. D., Friedlander, A. M., Gregg, A. K., Sandin, Due south. A., & Buckingham, One thousand. J. (2014). The origins of ambience biological sound from coral reef ecosystems in the Line Islands archipelago. The Journal of the Acoustical Society of America, 135(4), 1775-1788.
Freeman, South. East., Buckingham, Grand. J., Freeman, L. A., Lammers, Thou. O., & Gerald, Fifty. D. (2015). Cross-correlation, triangulation, and curved-wavefront focusing of coral reef sound using a bi-linear hydrophone array. The Journal of the Acoustical Society of America, 137(1), thirty-41.
Knowlton, Northward., Brainard, R. E., Fisher, R., Moews, Thou., Plaisance, 50., & Caley, M. J. (2010). Coral reef biodiversity. Life in the Earth's Oceans: Diversity Distribution and Abundance, 65-74.
Lutts, R. H. (1985). Chemical fallout: Rachel Carson's Silent Bound, radioactive fallout, and the environmental motion. Environmental Review: Er, 211-225.
Rountree, R. A., Gilmore, R. G., Goudey, C. A., Hawkins, A. D., Luczkovich, J. J., & Mann, D. A. (2006). Listening to fish: applications of passive acoustics to fisheries science. Fisheries, 31(nine), 433-446.
Wimmer, J., Towsey, M., Roe, P., & Williamson, I. (2013). Sampling environmental acoustic recordings to determine bird species richness. Ecological Applications, 23(6), 1419-1428.
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