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.