Crustaceans need ears too!

A preponderance of marine bioacoustic work has been focused on marine mammals – whales, dolphins, and pinnipeds. This is in large part due to the “charismatic megafauna” paradigm where big, complicated animals with recognizable expressions attract most human interest.

While fish – particularly large or colorful species can capture our attention under this same rubric, most scientific research on fish is advanced due to their commercial importance. Critters further down on the ‘charisma scale’ even while equally complicated in their adaptations are typically not studied, so it was great to hear OCR pal and Biologist Erica Staaterman’s presentation on mantis shrimp at the recent “Acoustic Communication by Animals” Symposium.

Even better was that her work was picked up by “Science Daily” and distributed to a wider public.

The mantis shrimp are visually intriguing; being some 8” to 10” (and up to 15”) long with a pair of incredibly complicated eyes that can sort out twelve colors and reconcile polarized light. Some species visually communicate by modulating fluorescence on their bodies, and some species live in monogamous pairs for up to 20 years!

With all of these attributes it is likely that vision is their dominant perceptual adaptation, but Erica found that they also communicate with sound through a low frequency rumble or purr. In the realm of human perceptions this isn’t Grammy material, but when pitch-shifted up an octave the call and response patterns become more apparent.

She also found that listening to the shrimp was very different in the wild from listening to them in a tank. The shrimps’ communications were, “so synchronized they sounded like a chorus.”

We can only speculate what they are expressing with these sounds, but Erica’s work has rolled back just a little more of the mystery of the deep. [Read Ocean-Noise post on ‘chorusing’]

Her paper was published in Aquatic Biology.

Acoustic Communication by Animals

Photo by "mali mish" on Flickr

Photo by Joe Shlabotnik on Flickr

I’ve just returned from a conference on “Acoustic Communication by Animals” at Cornell University. This was sort of a “vacation conference” for me as it was attended by a broad cross section of bio-acousticians outside of the usual marine mammals and fish folks found in the ocean noise-oriented meetings. With specialists in bats, birds, insects, frogs, hearing physiology and neurology etc., the meeting allowed me to indulge in my generalist predilections; in this case with a presentation on “chorusing.

Chorusing is usually defined as “acoustic signaling produced collectively by a group of individuals whose activity is clustered in both space and time… which may be temporally structured in alternating or synchronous formats.” The point of my paper was to expand the definition to:

Individual response to signals generated by another or other individuals within a group context that unifies the group in an aggregate behavior.

The reasoning behind this expanded definition is to move the discussion  outside of the usual “individual animal’s breeding and territory needs” and into a context of animals behaving as “acoustic communities.” I’m advancing this because I feel that animals subject to the impacts of human enterprise are much more than “bags of protein with behaviors” or “input devices” – definitions by which they often seem to be evaluated. This broader definition also helps explain the stunning flock behavior of starlings and equally stunning schooling behavior of sharks and forage fish.

In the presentation I qualify both of these behaviors as acoustically stimulated “spatial chorusing.” If you take an individual fish or bird out of these “choruses” and put them in a lab they cease being complete animals. While they are easier to evaluate as specimens, much of what community animals do – and how they are potentially compromised in their habitat by our actions – is lost in translation.

I believe that the aggregate behavior of an acoustic community can tell us much more about species vulnerabilities as well as resilience to human generated noise. Without this consideration we may be missing some opportunities.

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