Motorboat Noise Research Articles

Noise accelerates embryonic development in a key crab species: Morphological and physiological carryover effects on early life stages

Anthropogenic noise is considered one important global pollutant. The impact of noise on marine invertebrates has been less assessed. The present study evaluated the chronic effect of the motorboat noise obtained from a lagoon's soundscape, the natural habitat of the key crab Neohelice granulata, on its whole embryonic development, considering morphological and physiological carryover effects on embryos and hatched larvae. Results demonstrated that embryonic development was shortened under noise exposure. The effects on advanced embryos, larvae and adult females were: increased heartbeats and non-viable eggs, and decreased fecundity. Biochemical responses showed lipid peroxidation in embryos while antioxidant enzymes were activated in larvae and adults, indicating a counteracting effect related to the life stage. The negative effects on fitness offspring may imply ecological consequences at the population level. Results are discussed in terms of the ecosystem engineer species studied and the habitat, a MAB UNESCO Reserve lagoon, suggesting the urgent need to develop mitigation plans.

From behaviour to complex communities: Resilience to anthropogenic noise in a fish-induced trophic cascade

Sound emissions from human activities represent a pervasive environmental stressor. Individual responses in terms of behaviour, physiology or anatomy are well documented but whether they propagate through nested ecological interactions to alter complex communities needs to be better understood. This is even more relevant for freshwater ecosystems that harbour a disproportionate fraction of biodiversity but receive less attention than marine and terrestrial systems. We conducted a mesocosm investigation to study the effect of chronic exposure to motorboat noise on the dynamics of a freshwater community including phytoplankton, zooplankton, and roach as a planktivorous fish. In addition, we performed a microcosm investigation to test whether roach's feeding behaviour was influenced by the noise condition they experienced in the mesocosms. Indeed, compared to other freshwater fish, the response of roach to motorboat noise apparently does not weaken with repeated exposure, suggesting the absence of habituation. As expected under the trophic cascade hypothesis, predation by roach induced structural changes in the planktonic communities with a decrease in the main grazing zooplankton that slightly benefited green algae. Surprisingly, although the microcosm investigation revealed persistent alterations in the feeding behaviour of the roach exposed to chronic noise, the dynamics of the roach-dominated planktonic communities did not differ between the noisy and noiseless mesocosms. It might be that roach's individual response to noise was not strong enough to cascade or that the biological cues coming from the conspecifics and the many planktonic organisms have diverted each fish's attention from noise. Our work suggests that the top-down structuring influence of roach on planktonic communities might be resilient to noise and highlights how extrapolating impacts from individual responses to complex communities can be tricky.

Coral reef soundscapes and noise

Building back coral reefs requires limiting greenhouse gas emissions, limiting local threats, and active restoration. Vessel noise pollution is a widespread threat acting at a local level impacting a broad range of species from cetaceans to cephalopods. Ultimate consequences of noise pollution include death due to injury or predation, failure to develop and reduced offspring quality and survival. We tested the hypothesis that protecting coral reefs from motorboat noise can improve reproductive output in fish on the Great Barrier Reef in Australia. Across an entire breeding season, we limited motorboat traffic at three separate reefs with breeding spiny chromis. We compared these protected nests with nests on three further reefs where motorboats drove regularly nearby. We replicated the breeding experiment in a laboratory setting to isolate noise as the stimulus. Protecting coral reefs from traffic noise was beneficial for breeding fish and their offspring: egg fanning and offpsring growth were enhanced with lower energetic resource use, and reproductive success was enhanced. Limiting traffic noise at the local level presents a valuable opportunity for enhancing resilience in coral reefs by improving reproductive success in fish. This could speed up recovery following climate related mass mortality events caused by bleaching and cyclones.

From distraction to habituation: Ecological and behavioural responses of invasive fish to anthropogenic noise

AbstractTolerance to human‐induced environmental stressors is known to contribute to the spread and success of invasive species but their response to anthropogenic noise has still to be explored. Anthropogenic noise might modulate the trophic impact of invasive species and their competitiveness against native species.We used an ecological approach through the derivation of the functional response to test whether the strength of the trophic interaction between the invasive pumpkinseed sunfish andChaoboruslarvae was influenced by motorboat noise, with or without pre‐exposure.Boat noise decreased maximum feeding rate in the fish that never experienced boat noise before, resulting in a lower functional response compared to the ambient noise condition. We hypothesised that fish were distracted and reallocated a part of their finite attention to this new acoustic stimulus at the expense of prey processing.The distraction effect weakened with repeated exposure suggesting a habituation process. Although we cannot exclude persistent adjustments in behaviour, we did not find evidence for altered predation by fish pre‐exposed to boat noise.Pumpkinseed sunfish did not exhibit clear symptoms of a behavioural stress response.Chaoborusmovements were more numerous under boat noise but this was unlikely to influence trophic interaction strength relative to fish behaviour. Local species might experience increased trophic competition if they are disturbed and do not habituate contrary to invasive species.

A state-space model to derive motorboat noise effects on fish movement from acoustic tracking data

Motorboat noise is recognized as a major source of marine pollution, however little is known about its ecological consequences on coastal systems. We developed a State Space Model (SSM) that incorporates an explicit dependency on motorboat noise to derive its effects on the movement of resident fish that transition between two behavioural states (swimming vs. hidden). To explore the performance of our model, we carried out an experiment where free-living Serranus scriba were tracked with acoustic tags, while motorboat noise was simultaneously recorded. We fitted the generated tracking and noise data into our SSM and explored if the noise generated by motorboats passing at close range affected the movement pattern and the probability of transition between the two states using a Bayesian approach. Our results suggest high among individual variability in movement patterns and transition between states, as well as in fish response to the presence of passing motorboats. These findings suggest that the effects of motorboat noise on fish movement are complex and require the precise monitoring of large numbers of individuals. Our SSM provides a methodology to address such complexity and can be used for future investigations to study the effects of noise pollution on marine fish.

An Ecoacoustic Snapshot of a Subarctic Coastal Wilderness: Aialik Bay, Alaska 2019

I recorded the ambient sounds at three locations in the wilderness of Aialik Bay in Kenai Fjords National Park, Alaska between 25 June and 21 September 2019. My aim was to capture an ecoacoustic snapshot of the coastal soundscape to provide a comparable baseline for evaluating wilderness characteristics defined by the Wilderness Act of 1964. I visually and empirically characterized the Aialik Bay wilderness soundscape using the acoustic metrics of soundscape power (normalized watts/kHz) and Normalized Difference Soundscape Index (NDSI) from 5373 five-minute recordings, combined with visual and aural spectral examination of 4386 recordings. Soundscape power exhibited similar patterns across frequency intervals with sound sources primarily occurring in the low-frequency (1–2 kHz) and mid-frequency (2–5 kHz) intervals. Significant differences within frequency intervals between sites suggested the presence of distinct sonotopes. Low-frequency sounds were dominant across all three sites with peak soundscape power values across study days and 24 h timeframes attributed to wind and occasional periods of technophony emitted from commercial tour boats and private boating activities. Low-frequency geophony from wave action was ever present. Technophony exhibited some predictable patterns consistent with the timing of sightseeing boat tours. Peak values of soundscape power at mid-frequencies were attributed to the geophony of rain. Although biophonies were less common than geophonies, the choruses of songbirds were prevalent in July and promptly occurred daily between 0300 and 0600. Biophonies generally declined over the course of the day. All sites displayed negative NDSI values over most study days and consistently negative values over 24 h time frames, indicating a soundscape primarily influenced by low-frequency geophony and periods of technophony. However, NDSI values showed patterns and peaks similar to biophonies at mid-frequency intervals indicating biophony was still a notable contribution to this geophony-dominant soundscape. Despite the acoustic footprint of motorboat noise detected at all sample sites, the soundscape of the Aialik Bay wilderness was dominated by the natural sounds of geophony, biophony, and occasional periods of natural quiet indicative of a wilderness only partially impacted by technophony.

Are giant clams (Tridacna maxima) distractible? A multi-modal study.

To properly assess risk, an animal must focus its attention on relevant external stimuli; however, attention can be reallocated when distracting stimuli are present. This reallocation of attention may interfere with an individual’s ability to effectively assess risk and may impede its response. Multiple stimuli presented together can have additive effects as distractors, and these include stimuli in different modalities. Although changes in noise and water flow are detectable by some bivalves, this has not been studied in the context of risk assessment or distraction. We experimentally exposed giant clams (Tridacna maxima) to changes in water particle movement through underwater sound (motorboat noise) and increased water flow to determine whether these stimuli, individually or together, modified risk assessment or caused distraction. We found that clams responded to sound, flow, and their combination by increasing frequency of mantle retractions (a potential anti-predator response) when exposed to a stimulus. Sound alone did not change risk assessment in either the latency to close or to reemerge following closure. However, when exposed to both stimuli simultaneously, clams increased their latency to close. We suggest that clams perceive sound and flow in an additive way, and are thus distracted. Interestingly, and uniquely, clams discriminate these multimodal stimuli through a single sensory modality. For sessile clams, anthropogenic noise is detectable, yet unavoidable, suggesting that they be especially vulnerable to marine noise pollution.

Assessing and mitigating impacts of motorboat noise on nesting damselfish

Motorboats are a pervasive, growing source of anthropogenic noise in marine environments, with known impacts on fish physiology and behaviour. However, empirical evidence for the disruption of parental care remains scarce and stems predominantly from playback studies. Additionally, there is a paucity of experimental studies examining noise-mitigation strategies. We conducted two field experiments to investigate the effects of noise from real motorboats on the parental-care behaviours of a common coral-reef fish, the Ambon damselfish Pomacentrus amboinensis, which exhibits male-only egg care. When exposed to motorboat noise, we found that males exhibited vigilance behaviour 34% more often and spent 17% more time remaining vigilant, compared to an ambient-sound control. We then investigated nest defence in the presence of an introduced conspecific male intruder, incorporating a third noise treatment of altered motorboat-driving practice that was designed to mitigate noise exposure via speed and distance limitations. The males spent 22% less time interacting with the intruder and 154% more time sheltering during normal motorboat exposure compared to the ambient-sound control, with nest-defence levels in the mitigation treatment equivalent to those in ambient conditions. Our results reveal detrimental impacts of real motorboat noise on some aspects of parental care in fish, and successfully demonstrate the positive effects of an affordable, easily implemented mitigation strategy. We strongly advocate the integration of mitigation strategies into future experiments in this field, and the application of evidence-based policy in our increasingly noisy world.

Going the Distance: Influence of Distance Between Boat Noise and Nest Site on the Behavior of Paternal Smallmouth Bass

The effects of anthropogenic noise have garnered significant attention in marine ecosystems, but comparatively less is known about its impacts on freshwater ecosystems. For fish that provide parental care, the effects of acoustic disturbance could have fitness-level consequences if nest tending behavior is altered. This study explored the effects of motorboat noise on the parental behavior of nesting male smallmouth bass (Micropterus dolomieu; Lacepede, 1802), an important freshwater game fish in North America that provides sole paternal care to offspring. Specifically, we evaluated how boat noise proximity to a bass nest (ranging from 4.5 to 90 m) influenced paternal care behaviors. A total of 73 fish were exposed to a 3-min motorboat playback designed to simulate a boat sound that typically occurs in areas near littoral nesting sites. The fish were video recorded, and their behaviors were analyzed before, during, and after exposure to the playback. Residency time was the only behavioral metric to be adversely affected by noise playbacks but only when in close proximity to the speaker. Our results suggest that boat noise may have an impact on bass reproductive fitness in specific contexts where combustion motors are used near shore during the nesting period. The largely null findings may indicate a resilience to boat noise and/or habituation to the noise. In addition, boats displace water and create waves that represent another form of disturbance that could be experienced by fish but was not simulated here. Future research should integrate behavioral and physiological responses to boat noise and other aspects of boat disturbance to better understand the fitness impacts of boating activity on freshwater fish.

Hormonal and behavioural effects of motorboat noise on wild coral reef fish

Anthropogenic noise is an emergent ecological pollutant in both terrestrial and aquatic habitats. Human population growth, urbanisation, resource extraction, transport and motorised recreation lead to elevated noise that affects animal behaviour and physiology, impacting individual fitness. Currently, we have a poor mechanistic understanding of the effects of anthropogenic noise, but a likely candidate is the neuroendocrine system that integrates information about environmental stressors to produce regulatory hormones; glucocorticoids (GCs) and androgens enable rapid individual phenotypic adjustments that can increase survival. Here, we carried out two field-based experiments to investigate the effects of short-term (30 min) and longer-term (48 h) motorboat-noise playback on the behaviour, GCs (cortisol) and androgens of site-attached free-living orange-fin anemonefish (Amphiprion chrysopterus). In the short-term, anemonefish exposed to motorboat-noise playback showed both behavioural and hormonal responses: hiding and aggression increased, and distance moved out of the anemone decreased in both sexes; there were no effects on cortisol levels, but male androgen levels (11-ketotestosterone and testosterone) increased. Some behaviours showed carry-over effects from motorboat noise after it had ceased, and there was no evidence for a short-term change in response to subsequent motorboat-noise playback. Similarly, there was no evidence that longer-term exposure led to changes in response: motorboat noise had an equivalent effect on anemonefish behaviour and hormones after 48 h as on first exposure. Longer-term noise exposure led to higher levels of cortisol in both sexes and higher testosterone levels in males, and stress-responses to an additional environmental challenge in both sexes were impaired. Circulating androgen levels correlated with aggression, while cortisol levels correlated with hiding, demonstrating in a wild population that androgen/glucocorticoid pathways are plausible proximate mechanisms driving behavioural responses to anthropogenic noise. Combining functional and mechanistic studies are crucial for a full understanding of this global pollutant.

Noise‐induced reduction in the attack rate of a planktivorous freshwater fish revealed by functional response analysis

AbstractAnthropogenic noise can affect animals physically, physiologically, and behaviourally. Although individual responses to noise are well documented, the consequences in terms of community structure, species coexistence, and ecosystem functioning remain fairly unknown.The impact of noise on predation has received a growing interest and alterations in trophic links are observed when animals shift from foraging to stress‐related behaviours, are distracted by noise, or because of acoustic masking. However, the experimental procedures classically used to quantify predation do not inform on the potential demographic impact on prey.We derived the relationship between resource use and availability (the functional response) for European minnows (Phoxinus phoxinus) feeding on dipteran larvae (Chaoborussp.) under two noise conditions: ambient noise and ambient noise supplemented with motorboat noise. The shape and magnitude of the functional response are powerful indicators of population outcomes and predator–prey dynamics. We also recorded fish behaviour to explore some proximate determinants of altered predation.For both noise conditions, fish displayed a saturating (typeII) functional response whose shape depends on two parameters: attack rate and handling time. Boat noise did not affect handling time but significantly reduced attack rate, resulting in a functional response curve of the same height but with a less steep initial slope. Fish exhibited a stress‐related response to noise including increased swimming distance, more social interactions, and altered spatial distribution.Our study shows the usefulness of the functional response approach to study the ecological impacts of noise and illustrates how the behavioural responses of predators to noise can modify the demographic pressure on prey. It also suggests that prey availability might mediate the negative effect of noise on predation. Community outcomes are expected if the reduced consumption of the main food sources goes with the overconsumption of alternative food sources, changing the distribution pattern of interaction strengths. Predation release could also trigger a trophic cascade, propagating the effect of noise to lower trophic levels.

Boat noise affects the early life history of two damselfishes

Anthropogenic noise can have a negative effect on the physiology and survival of marine fishes. Most research has focused on later life-stages, and few studies have investigated the effects of human-induced noise on embryogenesis. The current study investigated whether playback of motorboat noise affected the embryogenesis of the coral reef damselfishes, Amphiprion melanopus and Acanthochromis polyacanthus. Embryos reared under the playback of boat noise had faster heart rates compared to the ambient reef controls. The effects of noise on morphological development differed between species and the fundamental interrelationships between early life history characteristics changed dramatically under boat noise for Ac. polyacanthus. Noise treatments did not alter the survival rates of embryos under laboratory conditions. Although species specific, our findings suggest that anthropogenic noise causes physiological responses in fishes during embryogenesis and these changes have direct impacts on their development and these alterations may have carry-over effects to later life stages.

Recreational boat traffic effects on fish assemblages: First evidence of detrimental consequences at regulated mooring zones in sensitive marine areas detected by passive acoustics

We assess the impact of recreational boat traffic on sensitive habitats in the Western Mediterranean using passive acoustics. We compared underwater sounds in three regulated mooring locations vs a pristine location; and temporal differences in the pristine location vs the nearest mooring between high and low touristic seasons. We measured the number of pulses/minute, fish pulse patterns, and percentage of boat noise occurrence and its relative average power level. At the pristine location, the call rates and their complexity were significantly higher and the motorboat noise was significantly lower. The temporal trend of biophonic sounds decreased significantly in the pristine location. In contrast, in the mooring sites, the motorboat noise decreased significantly and the fish calls remained at low levels in both seasons. In conclusion, motorboat noise negatively affects the complexity of the fish assemblages but could be conditioned to their historic uses.

Fish in habitats with higher motorboat disturbance show reduced sensitivity to motorboat noise.

Anthropogenic noise can negatively impact many taxa worldwide. It is possible that in noisy, high-disturbance environments, the range and severity of impacts could diminish over time, but the influence of previous disturbance remains untested in natural conditions. This study demonstrates the effects of motorboat noise on the physiology of an endemic cichlid fish in Lake Malawi. Exposure to motorboats (driven 20–100 m from fish) and loudspeaker playback of motorboat noise both elevated the oxygen-consumption rate at a single lower-disturbance site, characterized by low historic and current motorboat activity. Repeating this assay at further lower-disturbance sites revealed a consistent effect of elevated oxygen consumption in response to motorboat disturbance. However, when similar trials were repeated at four higher-disturbance sites, no effect of motorboat exposure was detected. These results demonstrate that disturbance history can affect local population responses to noise. Action regarding noise pollution should consider the past, as well as the present, when planning for the future.

Boat noise impacts risk assessment in a coral reef fish but effects depend on engine type

Human noise pollution has increased markedly since the start of industrialization and there is international concern about how this may impact wildlife. Here we determined whether real motorboat noise affected the behavior, space use and escape response of a juvenile damselfish (Pomacentrus wardi) in the wild, and explored whether fish respond effectively to chemical and visual threats in the presence of two common types of motorboat noise. Noise from 30 hp 2-stroke outboard motors reduced boldness and activity of fish on habitat patches compared to ambient reef-sound controls. Fish also no longer responded to alarm odours with an antipredator response, instead increasing activity and space use, and fewer fish responded appropriately to a looming threat. In contrast, while there was a minor influence of noise from a 30 hp 4-stroke outboard on space use, there was no influence on their ability to respond to alarm odours, and no impact on their escape response. Evidence suggests that anthropogenic noise impacts the way juvenile fish assess risk, which will reduce individual fitness and survival, however, not all engine types cause major effects. This finding may give managers options by which they can reduce the impact of motorboat noise on inshore fish communities.

Motorboat noise disrupts co-operative interspecific interactions

Human-made noise is contributing increasingly to ocean soundscapes. Its physical, physiological and behavioural effects on marine organisms are potentially widespread, but our understanding remains largely limited to intraspecific impacts. Here, we examine how motorboats affect an interspecific cleaning mutualism critical for coral reef fish health, abundance and diversity. We conducted in situ observations of cleaning interactions between bluestreak cleaner wrasses (Labroides dimidiatus) and their fish clients before, during and after repeated, standardised approaches with motorboats. Cleaners inspected clients for longer and were significantly less cooperative during exposure to boat noise, and while motorboat disturbance appeared to have little effect on client behaviour, as evidenced by consistency of visit rates, clientele composition, and use of cleaning incitation signals, clients did not retaliate as expected (i.e., by chasing) in response to increased cheating by cleaners. Our results are consistent with the idea of cognitive impairments due to distraction by both parties. Alternatively, cleaners might be taking advantage of distracted clients to reduce their service quality. To more fully understand the importance of these findings for conservation and management, further studies should elucidate whether the efficacy of ectoparasite removal by cleaners is affected and explore the potential for habituation to boat noise in busy areas.

Motorboat noise impacts parental behaviour and offspring survival in a reef fish.

Anthropogenic noise is a pollutant of international concern, with mounting evidence of disturbance and impacts on animal behaviour and physiology. However, empirical studies measuring survival consequences are rare. We use a field experiment to investigate how repeated motorboat-noise playback affects parental behaviour and offspring survival in the spiny chromis (Acanthochromis polyacanthus), a brooding coral reef fish. Repeated observations were made for 12 days at 38 natural nests with broods of young. Exposure to motorboat-noise playback compared to ambient-sound playback increased defensive acts, and reduced both feeding and offspring interactions by brood-guarding males. Anthropogenic noise did not affect the growth of developing offspring, but reduced the likelihood of offspring survival; while offspring survived at all 19 nests exposed to ambient-sound playback, six of the 19 nests exposed to motorboat-noise playback suffered complete brood mortality. Our study, providing field-based experimental evidence of the consequences of anthropogenic noise, suggests potential fitness consequences of this global pollutant.

Juvenile damselfish are affected but desensitize to small motor boat noise

Anthropogenic noise pollution is rapidly increasing in the marine environment. Anthropogenic noise can mask biotic sounds, disrupting the successful transmission between caller and receiver, and can cause physical, physiological and behavioural changes in some species. The effect of noise pollution produced by small motorboats is of particular interest in shallow, coastal habitats where vessel numbers are steadily increasing. The present field study examined the effect of small motorboat noise on the behaviour of the juvenile common damselfish, Pomacentrus amboinensis, and their potential to perform typical behaviours when presented with increased noise over a short time period. Behavioural observations in the field (before, 1, 10 and 20min after the start of boat noise) found there was an immediate decrease in the boldness and relative distance moved by P. amboinensis in response to the noise produced by a boat with a 30hp 2-stroke engine travelling 30–80m away. However, fish appeared to return to pre-boat noise exposure behaviours within 20min. The immediate change in behaviour may alter mortality rates in the short-term, but the potential for de-sensitization to boat noise may allow long-term persistence in noisy environments if they survive the initial disruption.

Effects of motorboat noise on foraging behaviour in Eurasian perch and roach: a field experiment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 564:115-125 (2017) - DOI: https://doi.org/10.3354/meps11997 Effects of motorboat noise on foraging behaviour in Eurasian perch and roach: a field experiment Carin Magnhagen1,*, Kajsa Johansson1, Peter Sigray2 1Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden 2Department of Underwater Research, Swedish Defence Research Institute, 164 90 Stockholm, Sweden *Corresponding author: carin.magnhagen@slu.se ABSTRACT: The negative impact of anthropogenic noise on marine animals is receiving increasing attention. In order to study the effect of motorboat noise on foraging behaviour in fish, we chose 2 species with different hearing abilities. The roach Rutilus rutilus has a better developed sense of hearing than the Eurasian perch Perca fluviatilis. The study took place in an inlet of the Bothnian Sea where boat traffic is almost absent. Groups of 6 fish were placed in field enclosures containing either one of the species or equal numbers of perch and roach. Half of each enclosure was covered with artificial vegetation. The fish were fed with pieces of saithe twice a day, both with and without the disturbance of an outboard motor. Sound pressure level and particle acceleration were measured for the motor, which was run at 2000 rpm. The trials were repeated for 5 d. Perch made fewer feeding attempts during noise exposure compared to controls in the single-species enclosures. As the experiment progressed, they gradually increased feeding and time spent in the open area, both with and without noise, indicating habituation. Habitat utilization was affected by the interaction of noise exposure and day. Roach responded to noise exposure with fewer feeding attempts, higher latency to enter the open area, and longer time spent in the vegetation compared to the controls without noise. Roach behaviour changed with time only when housed together with perch. This study, using authentic sound in a natural habitat, shows that noise exposure may affect the feeding behaviour of fish, that the response is species-specific, and that habituation and the presence of other species may modify the effects. KEY WORDS: Anthropogenic noise · Feeding activity · Field enclosures · Perca fluviatilis · Rutilus rutilus · Sound disturbance Full text in pdf format Supplementary material PreviousNextCite this article as: Magnhagen C, Johansson K, Sigray P (2017) Effects of motorboat noise on foraging behaviour in Eurasian perch and roach: a field experiment. Mar Ecol Prog Ser 564:115-125. https://doi.org/10.3354/meps11997 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 564. Online publication date: February 03, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Repeated exposure to noise increases tolerance in a coral reef fish

Some anthropogenic noise is now considered pollution, with evidence building that noise from human activities such as transportation, construction and exploration can impact behaviour and physiology in a broad range of taxa. However, relatively little research has considered the effects of repeated or chronic noise; extended exposures may result in habituation or sensitisation, and thus changes in response. We conducted a field-based experiment at Moorea Island to investigate how repeated exposure to playback of motorboat noise affected a coral reef fish (Dascyllus trimaculatus). We found that juvenile D. trimaculatus increased hiding behaviour during motorboat noise after two days of repeated exposure, but no longer did so after one and two weeks of exposure. We also found that naïve individuals responded to playback of motorboat noise with elevated ventilation rates, but that this response was diminished after one and two weeks of repeated exposure. We found no strong evidence that baseline blood cortisol levels, growth or body condition were affected by three weeks of repeated motorboat-noise playback. Our study reveals the importance of considering how tolerance levels may change over time, rather than simply extrapolating from results of short-term studies, if we are to make decisions about regulation and mitigation.