Effect of Sound Waves on the Invertebrates Behavior

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An examination on the behavior of shrimps and crabs when exposed to sound within an enclosed environment.

Problem Statement: Do sound waves, when consistently projected towards invertebrates within an enclosed environment, result in their avoidance of that particular area?

Relevance of your testable question

As humanity continues to expand its activity to encompass more and more areas around the world the result has been a subsequent expansion of activity into previously secluded habitats of various marine organisms. With this expansion has of course come the daily sounds associated with human activity such as the sounds of ship engines, the noise heard during the construction of an offshore oil platform or even the regular sound created by people within a general area. The inherent problem with this sound is that it is a form of stressor, namely, an outside factor that affects the ability of marine organisms to continue with their normal activities due to the effect of this outside form of interference.

The inherent problem such a concept is that in most cases where a stressor is consistently applied to a particular environment the result usually results in marine organisms, especially invertebrates, leaving the immediate area. In the case of this particular study what will be examined is if sound can act as an effective stressor for invertebrates to actually cause them to avoid a particular area. It is believed that the results of this study will show that the sounds created by normal human activity within a given area cause marine organisms to avoid it thus precipitating a slow deterioration of the environmental balance within a given area.

Literature review

Marine invertebrates do not actually “hear” in the conventional sense, they lack the external sensory organs commonly associated with hearing to actually hear in the same way that various other species do. Various studies do show that they do respond to sound, as such this indicates that there must be some form of “hearing” taking place that causes them to perceive the sound itself. An examination of the interior workings of marine invertebrates shows that they possess organs known as chordotonal organs which act as a form of internal “mechanoreceptor”.

What this means is that these particular organs sense cues normally associated with sound such as vibration since these organs are also utilized as a means of detecting various forms of pressure, movement and tension. The perceived reaction of invertebrates to sound is the result of them perceiving the sound as an external reaction caused by either a predator, prey or natural occurrence within the environment. This triggers a particular response to either hide or investigate the source of the sound. It must be noted that in various cases it has been shown that the higher the decibel level of the noise produced the greater the tendency for invertebrates to avoid the sound due to an apparent association with either a large predator or a sudden natural calamity.

Experiments conducted by Boehlert and Gill investigating the effect of sounds on marine organisms within a given area reveal that on average marine organisms that react to large noises through avoidance tend to avoid a certain area depending on the given noise intensity threshold produced (Boehlert Gill, 2010). Similarly, Gero Vella in his experiments involving the effect offshore wind farms have on local marine environments show that certain decibel levels do indeed affect marine organisms, especially invertebrates, wherein decibel levels over 180db or more within a given area are sufficient to scare away certain types of marine organisms within a small enclosed area (Vella, N.I.).

Based on this it can be seen that depending on the level of sound produced marine organisms can and will avoid a certain area due to their instinctual “flight” mechanism (referring to the fight or flight mechanism) associated with large vibrations created by distinct sounds being associated with a large predator or natural event. It must be noted that while such experiments show that marine invertebrates do avoid sound none of them mention what happens when the sound is removed and reintroduced at a given rate.

Experimental design

Step in the Experimental Procedure

Based on the lack of data regarding what might occur when sound is introduced and then taken away at a given rate what this experiment will seek to accomplish is to examine the behavioral reactions of various invertebrate species when sound is introduced into an enclosed environment at different intervals.

Step 1

Various live invertebrate species need to be obtained to accomplish the results of the experiment. Local fish markets within the general area have live specimens of crabs and certain types of shrimp available that can be utilized for this experiment. In order to better recreate their natural environment seawater will need to be procured which is also available at the fish market since this is what is used to keep the specimens alive during transport.

Step 2

A large pail roughly 3 feet tall and with a diameter of 15 inches will be used as the recreation for the natural environment. To ensure that the only external factor in this experiment will be sound waves, the exterior of the pail will be wrapped in black felt paper and the top covered with a lid in order to ensure that the only influencing factor in this experiment will be sound.

Step 3

The seawater along with the live shrimp and crabs will be placed into the pail and given at least 2 hours recuperation time to ensure that they will be ready enough to endure the experiment.

Step 4

Two large speakers will be procured and used to simulate the effect of sound in their natural environment. The speakers will be placed in alternating areas throughout the outside of the pail in order to simulate the effects of sound coming from different directions in the natural habitat of the shrimps and crabs.

Step 5

The type of music for this particular experiment to simulate the sounds of natural human activity within a given area will be Rammstein by the band “Rammstein” as shown in the following YouTube.

The reason why this particular song was chosen was due to the level of acoustic vibrations caused by the speakers when it was tested early on.

Step 6

After the Speakers have been placed and the experimental subjects have been given enough rest the experiment will begin. The speakers will be played at a volume of 180 decibels for approximately 5 minutes in one location then turned off and transferred for another location and played again for another 5 minutes. During the end of each alteration, the lid of the experimental environment shall be lifted to observe the behavior of the crabs and shrimps inside to see whether the music has any discernable effect on their behavior. This process will continue until 4 different directions have been achieved and their results recorded.

The reason why this particular experimental design was chosen above all others was because it was the only method of feasibly recreating the needed environmental conditions needed to effectively examine the behavior of invertebrates when sound is introduced into their natural habitat. Attempting to do so without the aid of an enclosed and controllable environment could fail the experiment due to numerous outside various possible contaminating the results.

Measuring the Reaction of the Invertebrates

In this particular experiment is assumed that the behavioral response of the various organisms utilized in this experiment will take the form of movement. With one of the dependent variables being the consistently in sound levels (160 DBS), it is assumed that by exposing the subjects to the same sound yet at varying directions the result will be that the subjects will either move toward or avoid the sound by moving away. In order to prove that the subjects moved a ruler will be placed at the bottom of the container to measure the degree by which the subjects actually moved. The experimental procedure measurement will proceed by first taking note of the current location of the subjects before the music is applied then taking note of their location after it is applied. The resulting movement either away or toward the music will serve as the experimental results.

Tools utilized in the Experiment

The tools utilized in this particular experiment are nothing more than 2 common rulers. One to measure the rate of movement from North to south while the other measures movement from East to West. The degree of movement will be measured utilizing inches since it was decided that centimeters would be far too troublesome to determine. Other units of measure were not needed since throughout the experimental procedure all factors were controlled such as the level of sound and the amount of outside environmental factors.

3. The controlled variables in this particular experiment consisted of the environment that the experimental subjects were in, the temperature of the water which remained at room temperature and the level of sound coming from the speakers which remained at a constant 160 DBS throughout the experiment. The dependent variable in this particular study consisted of the distance traveled by the experimental subjects in each direction as the sound was applied. While the independent variable itself is the different rates of distance traveled by the experimental subjects since each responded in a slightly different way (as indicated by distance traveled) in some instances throughout the data gathering step of the experiment.

It must be noted that while this experiment could utilize a method of experimentation wherein different sound levels can be used the fact remains that based on the data of Vella sounds lower than 180 dB probably could not sufficiently produce enough of a reaction in invertebrate species to cause them to produce any behavioral changes. It is due to this that 160 DBS was the chosen sound level for the dependent variable since by put the speakers close enough to the pail this should cause enough transference from sounds waves to a vibrational reaction in the water to elicit a reaction from the experimental subjects.

4. In order to reduce threats to the internal validity of the study, certain precautions will be undertaken to ensure that the only means of interaction between the test subjects and the outside world will just be the sounds from the speakers. First off light as a method of eliciting a reaction will be blocked off completely from the pail using black felt paper. Secondly, a glass lid will be placed over the pail with black felt paper covering the other side to simulate total darkness. It is in this particular environment where nearly all external stimuli are blocked off that the experiment will proceed with the introduction of the external factor of sound. It is expected that utilizing this particular method all external threats to internal validity will be prevented thus ensuring the integrity of the experiment.

Hypothesis

It is the hypothesis of this experiment that by introducing sound waves at different intervals from various directions that the experimental subjects of this experiment will move away from the sound. This particular hypothesis is based on the data Boehlert and Gill investigated regarding the effect of sounds on marine organisms wherein the introduction of sound within a given area can cause enough of a vibrational reaction to actually cause various marine animals to move away due to the “flight” instinct regarding the connection between large vibrations and danger.

Process of Data Collection

Experiment Photos

(Seen here are the live crabs without the shrimp and seawater placed in)

During the experiment, it was discovered that the bucket utilized was too small for the crabs or shrimp to effectively move around in due to the lack of space. An alternative container had to be utilized that had enough space for the various experimental subjects to move around in. A small used red container was found and covered with a plastic bag since the felt paper bought turned out to be unnecessary for both the bucket and the container.

The process of data collection for the experiment was relatively straightforward. On each corner of the box, music was played at approximately 160 decibels as close to the box as possible. Before the start of each experiment, a stick was used to move the experimental subjects close enough to the side of the box where the music was to be played and then the experiment was covered. The music was played for 5 minutes on each side and the distance traveled by the experimental subjects from the side of the box where the music was played was measured by a ruler placed inside the box.

Methods of Data Collection

The quantitative data were collected utilizing a ruler that placed in the container beforehand to measure the degree of distance traveled between the side where the music was playing and the rate in which the experimental subjects traveled away from it. No complicated methods of measurement were required since this was a relatively straightforward process examining the “flight” mechanism of invertebrates when exposed to relatively high sounds resulting in vibrations in the water.

Results of Experiment

Decibel Level	Crabs (Inches Moved)	Shrimp (Inches Moved)
160db (Left Side)	4 Inches to the right	2 Inches to the right
160db (Right Side)	2 inches to the left	2 inches to the left
160db (Top)	3 inches down	1 inch down
160db (Bottom)	2 inches up	1 inch up

Experimental Subject Movement Chart

Experiment Results

The result of the experiment shows that utilizing 160 decibels of sound over a prolonged period placed directly against a container does indeed cause enough of a vibrational reaction in the water over a prolonged period to elicit a reaction from the experimental subjects. The results of the experiment clearly show that over 5 minutes the shrimp and crabs moved away from the jarring sound which indicates that invertebrate organisms do move away from areas where there is a prolonged and persistent level of a particular high decibel level.

While this experiment did not intend to measure the level of sensitivity of the organisms the results do show that due to the distance traveled crabs are more sensitive to shrimp when it comes to a reaction to sound. This may be due to the more complex sensory organs in crabs as compared to shrimps and as such indicates that more complex organisms will have a higher tendency to move away from areas of high decibel levels as compared to other creatures.

Conclusion

The results of the experiment show that by introducing a high level of constant sound in a particular direction the resulting behavioral response from invertebrate organisms is to move away from the loud noise. This is shown by the varying directions shown in the experimental results where it can be seen that a certain degree of movement away from the offending sound can be noticed. This result supports the hypothesis based on the data provided by Boehlert and Gill that sound waves have a distinct effect on marine organisms, particularly invertebrates, where the characteristic vibrations produced are attributed to danger in the surrounding environment. The resulting movement away from the sound as seen in the experiment is thus attributed to the “flight” mechanism in marine invertebrates.

The experimental design was a key factor in proving this hypothesis since through the utilization of loudspeakers as a method of replicating the sounds of persistent human activity it can be seen that areas, where there are large concentrations of structures being built such as offshore oil platforms or areas, traversed regularly by ships causes a sufficient level of high decibel sound that this in effect causes invertebrate creatures to leave the area causing a subsequent change in the local ecosystem. In order to verify the results of this experiment all a person would need to do is obtain the same experimental subjects and subject them to the same decibel level utilized in this experiment over the same prolonged period to replicate the results. It is expected that through a replication of the features of the experiment wherein the same result is produced this would prove the validity of the results of the experiment and further cement the findings of this study.

Reference List

Boehlert, G, & Gill, A. (2010). The environmental and ecological effects of ocean renewable energy. Oceanography, 23(2), 68-79.

Vella, G. (N.I.). The environmental impacts of offshore wind generation. Center for Marine and Coastal Studies, 126 – 129.

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