Anthropogenic noise pollution and its effects on Chromis chromis schools
Athena Barrios & Sage Melcer 2012
Abstract
The Mediterranean damselfish Chromis chromis has been proven to be affected by
anthropogenic noise produced by boats emitting frequencies similar to those that males produce
when participating in mating behaviors. Our experimental design was to examine if adult C.
chromis were sensitive to all frequencies produced by boating noise, and the general hearing
sensitivity of the juvenile C. chromis. We used a combination of individuals tested in a
controlled tank setting along with a field study of schooling behavior. We exposed C. chromis to
various frequency levels in order to determine the effect of human-induced sound on their
population. Through our analysis we determined there was substantial evidence that both
juvenile and adult C.chromis operated under the same frequency as boat motors, and the
presence of boating noise would have a negative effect on the adult schools.
Introduction
Sound plays a key role in the lives of various species of marine organisms. It can be used
as a means of communication between individuals, a tool utilized in attracting mates or
defending territories, and as a weapon of survival to catch food and evade predators. Due to the
wide range of uses for underwater sound the hearing range of different species is widely varied,
and is typically associated with behaviors the sound is used for. Fishes operate on a wide range
of different frequencies, anywhere from 20-1000 Hz, which are used to communicate amongst
each other and to acquire information about their environment (NOAA Fisheries, 2012).
The introduction of anthropogenic noise into aquatic environments has become an
increasing problem in coastal communities. Recreational and small fishing boats have shown to
operate on frequencies ranging from 100-1000 Hz, which is well within the operating frequency
of most fish species. However anthropogenic sounds are often produced at much more intense
sound pressure levels (SPL) then naturally found within a coastal ecosystem. Ambient SPL can
range from 90-110 dB, while boating vessels can produce sound of an intensity ranging from
110-140 dB. This exposure has shown to damage soft tissue, cause both temporary and
permanent threshold shifts, and alter feeding, mating, and settling behaviors (Hong Young Yan,
2010).
The damselfish Chromis chromis is the most abundant schooling fish in the
Mediterranean. They live in rocky reef habitats as well as over Posidonia beds, where they feed
on copepods in the water column and also small benthic organisms (Pinnegar et. al., 2007).
Juveniles are easy to spot with their electric blue coloration, but are normally seen lower in the
water column throughout the day as they spend most of their time near the rocks. Adults school
in shallow waters (0-50 ft.) during the day to feed, and hide themselves within the rocky reef at
night. During mating periods, males produce sound waves from 400-600 Hz to both attract
females to their nests and defend their territories from other males (Bracciali et al.). The
Mediterranean damselfish is zooplanktivorous and therefore a key component in carbon,
nitrogen, and phosphorus fixation for benthic coastal communities (Pinnegar et. al., 2007). Since
boating noise operates under the same frequencies as C. chromis do, there are projected effects
on their population.
Bracciali et al. 2012 found in areas of high levels with motorized boating activities, C.
chromis schools changed their feeding times from midday to evening hours, which is incredibly
inefficient in relation to their food source. Though the spectral signature of frequencies utilized
in mating behavior has been studied in adult C. chromis, other sensitivity ranges have yet to be
explored. Also, no study has examined the behavior associated with hearing sensitivity in
juvenile C. chromis. In other species of fishes, sound has been proven to have negative
consequences; including nutrient deficiency, decline in fitness, change in behavior, and a wide
variety of soft tissue damage that can lead to higher mortality rates within a population (Hong
Young Yan et. al., 2010).
The purpose of our research was to closely observe the behavior of Chromis chromis
changes in relation to the exposure of anthropogenic boating noise. By separating individuals of
both adult and juvenile C. chromis in a controlled tank setting, we were able to study the changes
in the behavior of the individual as frequency and decibel levels are manipulated. We then
compared this to the behavioral observations made in the field, to explain the displayed patterns
of disturbance that would lead to the feeding behavior explained by Bracciali et al. 2012.
Question: Is there an overlap between the auditory sensitivity of Chromis chromis adults and
juveniles and the sound emitted by motorized boating activity?
Hypothesis Number One: Juvenile and adult Chromis chromis are affected by the same
frequencies that are produced by boat motors.
Hypothesis Number Two: Chromis chromis will be negatively affected with an increase in
boating activity.
Prediction Number One: In a controlled lab setting, both juvenile and adult individuals will have
negative reactions to those frequencies produced by boat motors. However juveniles will be
more sensitive than adults.
Prediction Number Two: In the field, C. chromis schools will swim deeper in the water column
to escape the boat noise.
Materials & Methods
Lab Setup:
For our lab studies, we used a concrete, outdoor tank that had a total volume of 2.312 m3. It was
filled with 0.898 m3 of seawater during all tests. An extension cord was run from a power source
above the tank to power a receiver (5 channel digital amplifier-Kool Sound WMP-100). A laptop
was attached to the receiver, which used TruRTA software to generate various sets of
frequencies and decibels into the tank for testing. Raven Lite 1.0 sound analysis software was
used to record ambient sounds of our tank and field sites.
Lab Tests:
Our first round of testing was focused on the individual hearing sensitivity of juvenile
Chromis chromis. Four frequencies and five-decibel levels were used in a matrix to create 20
possible combinations of sound (Fig.1). Two groups of five fish were used to get two full
repetitions of the matrix. Ten individuals of juveniles and adults were tested to complete the
matrix of sound combinations for both age groups. We placed one juvenile in the tank by itself
and allowed five minutes for it to become accustomed to its surroundings. Four random
combinations of frequencies and decibels were then played to the individual for an exposure time
of one minute and a recovery period of three minutes. An underwater speaker (Fig. 2),was placed
in the right side of the tank and mounted to a piece of wood to stabilize the device. A meter tape
was placed at the bottom of the tank to track distances from the speaker. At the 1.3-meter mark,
we placed a rock structure for the C. chromis to aggregate. Notes were taken during every trial to
record the reaction of the fish towards the sounds. We defined a positive reaction as any
movement toward the speaker or emergence out of the rock complex. Neutral (or none) behavior
was noted when a fish was found hovering in the same spot wherever it was in the tank, near or
far from the sound. Negative behavior was most often associated with a fish swimming in the
opposite direction of the sound, hiding underneath the rocks at the center of the tank, or trying to
hide further into the crevices of the rock.
Figure 1: Matrix used for sound tests. Numbers 1-5 correspond to the combinations that individuals 1-5 received.
Numbers ranging from -20 to +20 are in decibels.
Figure 2: Outdoor tank that was used for sound tests with juvenile and adult Chromis chromis. Markers added in to
show scale of the tank and location of speaker.
Field-testing site:
For our field behavioral studies, we utilized the northern and southern harbor mouths. The
sampling area was based on where the highest density of C.chromis schools were found, located
above boulders and Posidonia beds at depths ranging from 25-30 ft. A 21 ft. aluminum skiff with
a Yamaha 4-stroke motor was used to drive over the schools of C. chromis and observe reactions
to sounds of the motor. A hydrophone (Aquarium Audio H2a) was dropped of the side of the
boat to record sounds of the motor at an average depth of 6m. Teams of three divers on SCUBA
were stationed at both North and South schools of C. chromis to observe the school’s reaction to
the boat passing over and revving its engine. Milk bottles were used as buoys to signal the boat
to the location and position of divers. Divers were responsible for recording the depth of the
band where the fish were most concentrated. The direction of dispersal and any other type of
observation made before and after the boat passed by were also noted. The boat passed a total of
three times over schools and then retreated to the harbor. Recordings of the engine revving,
idling and running were taken.
Figure 3: A Google Earth clip was taken to show the site where the boat was used. The yellow line represents the
path that the boat took during the trial. The lavender oval represents the main school of C. chromis that were
observed.
Results
Figure 4: This overlay plot shows the difference in behavioral response between adult and juvenile C.chromis to
different decibel levels emitted in the tank. Decibels on the x-axis and number of fish on the y-axis.
Figure 5: This overlay plot shows the same relationship as Figure 6 except frequency (Hz) is plotted on the x-axis.
Figure 6: This table is what displays the significant p-value being a function of stage*decibel*Hertz after looking at
the distribution of responses to all the sound combinations.
The behavioral data was separated between two graphs (Fig. 4 & 5) to show the
difference of reactions between adult and juvenile Chromis. When all factors are considered, we
saw a more positive response from the juvenile fish in both decibel and frequency graphs. Any
positive behavior was noted as movement toward the sound source or curious behavior
swimming out of the rock complex. There were more counts for negative and even neutral
behavior in the adult chromis regarding frequencies ranging from 200-1100 Hz. This could be
due to prior exposure to similar sounds in the water coming from boats traveling through
STARESO harbor. Positive behavior exhibited by the adult fish was seen at the extreme ends of
the tested frequencies, 200 and 1100 Hz. The highlighted row in Fig. 6 shows P= 0.0259, which
tells us that any significant response to the sound tests were seen as a combination of factors
including age of fish and the combination of decibels/hertz that were tested.
Frequency Analysis
Figure 7: This sound analysis overlay plot, shows the level of decibels emitted (X) in relation to the sound level of
decibels recorded (Y).
Figure 8: This sound analysis overlay plot compares the tank environment decibel recordings to those recorded
from the boat trials, both running and revving the engine.
The average decibel level recorded from each decibel level emitted was graphed on an X
and Y distribution and plotted using an overlay plot (Fig. 7). Due to the fact that the sound was
being played underwater in a fixed volume, the emitted frequency tones were magnified. This
allowed the controlled setting to mirror the sound levels of the field trials (Fig. 8). This graph
overlays the average decibel levels of the recordings taken from the boat with that of the
graphical representation of the decibel levels recorded in the outdoor tank. This shows that our
individually tested C. chromis were exposed to the same decibel levels per wavelength as those
tested in the field.
The field observations of Chromis schools’ reaction to the boat showed a negative
response to all movement and revving of the engine. Their initial depth was 12 ft below surface.
With every additional drive by of the boat, the schools would split up into smaller groups and
move downward, away from the sound. Resettlement of the school would happen relatively
quickly (within two minutes) but not in the same density as the original school. At the end of the
test, the final settlement depth was 19 ft from the surface.
Discussion
Of all the individuals tested, the juvenile Chromis had more distinct reactions compared
to the adults. They displayed more positive behavior which could be an indicator to their
curiosity of foreign sounds. It could be a curiosity driven response seeing as the younger
Chromis are not accustomed to the loud sounds produced by boats. The adults showed much
more resistance to the frequencies being played, especially those equal to or higher than 800 Hz.
There were little to no positive reactions seen in the adults most likely due to them associating
sound with previous anthropogenic noise exposure. The fact that there was any response from
these fish tells us that schools of Chromis are highly susceptible to being disturbed on a larger
scale in the wild. Although the only behavior that could really be observed in the tank was
swimming in the opposite direction or hiding under a rock, this leads us to believe that the fish
will be affected negatively when schooling during the day. What we were able to observe in the
tank supports our specific hypothesis that juvenile Chromis would be more sensitive to sound
disturbances.
In the field, the reaction to boat sounds resulted in a net downward movement of the
schools, which coincided with our second specific hypothesis. Chromis chromis are spending
more time dispersing and trying to resettle than they are feeding as a school. This could present a
positive feedback loop for this specific coastal ecosystem, particularly during the tourist season
or areas with little to no boating regulations. With more boats in the water, schools will be
spending more time dispersing and resettling during the peak feeding times. This will cause later
feeding times for Chromis schools and a shift in the nutrient exchange between pelagic and
benthic ecosystems (Bracciali et al. 2012).
Due to time limitations and poor weather conditions, we were only able to complete one
field study trial. The absence of repetition keeps us from having substantial evidence to support
our second hypothesis. However, the results that we did collect suggest that the presence of
boating noise in the area would cause a significant disturbance to the Chromis schools. A
potential follow up project would be to repeat the field study methods to gather more data. To
improve our lab study, it would have been extremely beneficial to have a quieter test sight. As a
result of limited tank size and space inside the wet lab, we used an outdoor tank that was large
but exposed to high levels of ambient noise. If this portion were to be repeated, a quieter testing
area would be ideal and lead to more accurate occurrences of positive or negative reactions.
Acknowledgements
We would like to extend our gratitude towards Pierre Lejeune, and all staff at STARESO
Research Institute of Oceanography for allowing us to use their facilities. We would like to
humbly thank our professors, Pete Raimondi and Giacomo Bernardi for their constant guidance
and support throughout the quarter and our TA’s Jimmy O’Donnell, Gary Longo, and Kristin De
Nesnera.
References
Bracciali, Claudia, Daniela Campobello, Cristina Giacoma, and Gianluca Sarà. "Effects of
Nautical Traffic and Noise on Foraging Patterns of Mediterranean Damselfish (Chromis
Chromis)." PLOS ONE (2012): n. pag. Web. 8 Dec. 2012.
Codarin, Antonio, Lidia E. Wysocki, Friedrich Ladich, and Marta Picciulin. "Effects of Ambient
and Boat Noise on Hearing and Communication in Three Fish Species Living in a Marine
Protected Area (Miramare, Italy)." Marine Pollution Bulletin 58.12 (2009): 1880-887.
ScienceDirect.com. Web. 11 Dec. 2012.
Domingues, Vera S., Giuseppe Bucciarelli, Vitor C. Almada, and Giacomo Bernardi. "Historical
Colonization and Demography of the Mediterranean Damselfish, Chromis Chromis." Molecular
Ecology 14.13 (2005): 4051-063.Wiley Online Library. 19 Sept. 2005. Web. 17 Oct. 2012.
Picciulin, Marta, Linda Sebastianutto, Antonio Codarin, Angelo Farina, and Enrico A. Ferrero.
"In Situ Behavioural Responses to Boat Noise Exposure of Gobius Cruentatus (Gmelin, 1789;
Fam. Gobiidae) and Chromis Chromis (Linnaeus, 1758; Fam. Pomacentridae) Living in a Marine
Protected Area." Journal of Experimental Marine Biology and Ecology 386.1-2 (2010): 125-32.
ScienceDirect.com. Web. 11 Dec. 2012.
Pinnegar, John K., Nicholas V.C. Polunin, John J. Videler, and Jos J. De Wiljes. "Daily Carbon,
Nitrogen and Phosphorus Budgets for the Mediterranean Planktivorous Damselfish Chromis
Chromis." Journal of Experimental Marine Biology and Ecology 352.2 (2007): 378-91.
ScienceDirect.com. Web. 11 Dec. 2012.
Southall, Brandon. "Estimated Auditory Bandwidths for Marine Mammals and Fish."NMFS
Memorandum Guidance on ESA-Listed Marine Mammal Consultations. N.p., n.d. Web. 17 Oct.
2012.
Yan, Hong Young, Kazuhiko Anraku, and Ricardo P. Babaran. "Hearing in Marine Fish and Its
Application in Fisheries." Behavior of Marine Fishes: Capture Process and Conservation
Challenges. N.p.: n.p., 2010. 45-64. Web. 8 Dec. 2012.