Kelp forests and underwater sound
What is underwater sound and why is it important?
Just like in air, many physical (e.g., waves crashing on shore), biological (e.g., whales singing), and human-driven (e.g., boat engines) phenomena produce sounds. Sound in sea water travels about 5x faster than sound in air (roughly 1500 m/s in sea water versus about 340 m/s in air), which allows sounds produced underwater to travel long distances. In fact, Woods Hole Oceanographic Institute scientists ran an experiment in 1944 and were able to hear underwater explosions from more than 900 miles away!
Similar to how humans and many other land animals use sound to communicate and gain information about their environments, so do many animals in the sea. Marine mammals are the most well-known biological producers of underwater sound, but fishes and invertebrates (i.e., animals without backbones) can also produce and communicate with underwater sound. Not only do adult marine animals use sound in the sea, but their dispersing larvae - the "babies" of fishes and invertebrates - use underwater sounds to find suitable habitat where they can settle and grow into adults. Thus, underwater sounds can influence the behavior and ecology of adult marine animals, as well as alter the future health of an ecological community by influencing where and when larvae settle.
How do we measure underwater sound?
Because of the importance of underwater sound, scientists have been interested in measuring it for quite a while, and to do that we use a tool called a hydrophone - basically an underwater microphone. These hydrophones can "hear" and record underwater sounds so that we can study them.
As part of our project, we propose to develop a low-cost, open-source hydrophone recorder. Commercial hydrophone units can be expensive, so we hope that by developing a low-cost unit, more scientists and citizens can delve into the world of underwater sound.
What sounds do we hear in the kelp forest?
The kelp forests off Southern California are full of life, and many of the species that call these kelp forests home produce sounds. The kelp forest soundscape (that is, all the sounds heard within the kelp forest) is incredibly dynamic and full of mammal, fish, and invertebrate sounds.
Many of the fishes that live in the kelp forests form spawning aggregations, where hundreds or thousands of fish come together for the sole purpose of mating. For example, kelp bass and giant sea bass form aggregations and use sound to find each other and indicate their readiness to mate.
In addition to fish, many invertebrates of the kelp forest produce sounds, too. The California spiny lobster produces a rasping sound (called a stridulation) by rubbing the base of its antennae against a portion of its carapace just beneath the eye. Lobsters "stridulate" when confronted by a predator (even humans!) to alert others and to help defend themselves. Sea urchins found in the kelp forest make noise when their mouthparts (which have the coolest name - Aristotle's lantern!) grind against the rocky substrate as they eat algae. In fact, when there are a lot of urchins in one area all eating at the same time, the noise can be so loud that we can hear it over five miles away!
Humans also contribute to the kelp forest soundscape! Kelp forests support vibrant recreational and commercial fisheries, as well as recreational and commercial diving industries. The noise from engines and boats on the water and divers exploring the kelp forest all add sounds to the environment.
Want to see more images and see what what other kelp forest research we have going on? Follow #KelpForestFridays on Twitter and Instagram!
So far, we have raised about 30% of our goal. We need to reach 100% by May 22nd or we will not get a single penny. Even if you are not able to contribute financially, please help us get the word out by sharing the Kelp Sound project with ten of your friends, co-workers and family! If 10 people share this project with 10 of their friends/co-workers/family, we will have reached 100 people!
Thanks again to all of those who have already supported this project! If you have any questions, please don't hesitate to ask us using the Ask the Scientists section or via Twitter @FishySounds or @underwaterjack.
-- Camille and Jack
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