Finding a home in the noise: cross-modal impact of anthropogenic vibration on animal search behaviour

Marine and Freshwater Sounds Impact Invertebrate Behavior and Physiology: A Meta-Analysis

The diversity of biotic and abiotic sounds that fill underwater ecosystems has become polluted by anthropogenic noise in recent decades. Yet, there is still great uncertainty surrounding how different acoustic stimuli influence marine and freshwater (i.e., aquatic) communities. Despite capabilities to detect and produce sounds, aquatic invertebrates are among the most understudied taxa within the field of soundscape ecology. We conducted a meta-analysis to understand how sounds from various sources influence the behavior and physiology of aquatic invertebrates. We extracted 835 data points from 46 studies conducted in 15 countries. The resulting data included 50 species, a range of experimental conditions, and four sound categories: anthropogenic, environmental, synthetic, and music. We used meta-analytic multivariate mixed-effect models to determine how each sound category influenced aquatic invertebrates and if responses were homogeneous across taxa. Our analyses illustrate that anthropogenic noise and synthetic sounds have detrimental impacts on aquatic invertebrate behavior and physiology, and that environmental sounds have slightly beneficial effects on their behavior. Defence responses were the most impacted behaviors, while the most prominent physiological responses were related to biochemistry, genetics, and morphology. Additionally, arthropods and molluscs exhibited the most pronounced physiological responses to anthropogenic and synthetic noise. These findings support the conclusion that many invertebrate species are sensitive to changes in aquatic soundscapes, which can cause adverse or favorable consequences to individuals and populations, dependent on the sound source. This quantitative synthesis highlights the necessity of including marine and freshwater invertebrates in acoustic exposure studies, aquatic ecosystem assessments, and emerging noise pollution policies.

Statocyst Ultrastructure in the Norwegian Lobster (Nephrops norvegicus)

Statocyst anatomy and fine morphology in Norwegian lobster (Nephrops norvegicus) are studied for the first time using scanning and transmission electron microscopy. N. norvegicus exhibits sensory setae projecting from the statocyst inner cavity floor into a mass of sand granules (statoconia) embedded in a gelatinous substance. The setae are distributed in four areas: a curved field made up of an inner single row and an outer double row that run on a circle around the medial and lateral rim of the central depression, a small setal field in the posterior part, a large setal field, opposite to the small field, and a short row, running internally and lying parallel to the inner single row, next to the small setal field. A study of the fine morphology of the statocyst sensory setae shows that the structure of the setae in the different areas is similar, with a bulb (the proximal portion of the sensillum), a setal shaft, a tooth (the smooth portion of the bulb), a fulcrum (a transverse fold), and filamentous hairs. The hair cells are firmly implanted within the cuticular layer. Although the type of innervation of the statocyst was not determined in the present study, the close taxonomic position of the lobster to that of the crayfish and crab would suggest that the setae in N. norvegicus are pure mechanoreceptors rather than sensory cells.

The effect of anthropogenic substrate-borne vibrations on locomotion of the fiddler crab Austruca lactea

The anthropogenic construction activities on the coasts, such as pile-driving, generate vibrations that propagate through the substrate. Such substrate-borne vibrations could potentially affect marine organisms inhabiting the benthic environments. However, there is a lack of documented studies on the effects of vibrations on benthic animals. To investigate whether anthropogenic substrate-borne vibrations such as pile-driving operation influence the fiddler crab, Austruca lactea, we measured their locomotion response under vibrations of 35, 120, 250, 500, and 750 Hz generated by a vibrator. We compared the locomotion of crabs between control and vibration-treatment groups using videography. The duration of movements was significantly lower under 120 Hz vibrations compared to the control. Moreover, crab velocity was significantly higher under vibrations of 120 Hz and 250 Hz compared to the control group. Our result suggests that A. lactea can detect low-frequency substrate-borne vibrations and experience stress, leading to increased energy consumption.

Effects of anthropogenic magnetic fields on the behavior of a major predator of the intertidal and subtidal zones, the velvet crab Necora puber

With the progress of the offshore renewable energy sector and electrical interconnection projects, a substantial rise in the number of submarine power cables is expected soon. Such cables emit either alternating or direct current magnetic fields whose impact on marine invertebrates is currently unknown and hardly studied. In this context, this study aimed to assess potential short-term exposure (30 min) effects of both alternating and direct magnetic fields of increasing intensity (72-304 μT) on the behavior of the high-ecological value velvet crab (Necora puber). Three experiments were designed to evaluate whether the strongest magnetic field intensities induce crabs' attraction or repulsion responses, and whether foraging and sheltering behaviors may be modified. We extracted from video analyses several variables as the time budgets crabs spent immobile, moving, feeding, or sheltering as well as total and maximal distance reached in the magnetic field (MF) gradient. The crabs exposed to artificial MF did not exhibit significant behavioral changes compared with those exposed to the "natural" MF. Overall, our results suggest that, at such intensities, artificial magnetic fields do not significantly alter behaviors of N. puber. Nevertheless, future studies should be conducted to examine the effects of longer exposure periods and to detect potential habituation or resilience processes.

Cross-sensory interference assessment after exposure to noise shows different effects in the blue crab olfactory and sound sensing capabilities

Underwater noise pollution is an increasing threat to marine ecosystems. Marine animals use sound in communication and orientation processes. The introduction of anthropogenic noise in their habitat can interfere with sound production and reception as well as with the acquisition of vital information through other sensory systems. In the blue crab (Callinectes sapidus), the statocyst is responsible for acoustic perception, and it is housed at the base of its first pair of antennae (antennule). The sensilla of the distal part of these antennule hosts the olfactory system, which is key for foraging. Given the anatomical proximity of the two sensory regions, we evaluated the possible interference of sound exposure with the crab ability to find food, by using an aquatic maze, and looked at the potential impairment of the righting reflex as well as at ultrastructural damages in statocysts. Although a significant effect was observed when looking at the time used by the animal to recover its habitual position ("righting reflex"), which was associated to lesions in the statocyst sensory epithelia, the time required to find food did not increase after the exposure to sound. When the crabs were exposed to natural sounds (marine background noise and sounds of their predators: Micropogonias undulates and Sciaenops ocellatus) they did not show significant differences in foraging behaviour. Although we found no unequivocal evidence of a negative impact of sound on olfactory capabilities, the study showed a clear righting reflex impairment correlated with ultrastructural damages of the statocysts. We argue that crab populations that cannot easily avoid noise sources due to their specific coastal distributions may incur in significant direct fitness costs (e.g. impairment of complex reflexes). This integrated approach to sound effect assessment could be used as a model for other invertebrate species to effectively monitor noise impact in marine environments.

Anthropogenic noise may impair the mating behaviour of the Shore Crab Carcinus Maenas

Anthropogenic noise is a recent addition to the list of human-made threats to the environment, with potential and established negative impacts on a wide range of animals. Despite their economic and ecological significance, few studies have considered the impact of anthropogenic noise on crustaceans, though past studies have shown that it can cause significant effects to crustacean physiology, anatomy, and behaviour. Mating behaviour in crustaceans could potentially be severely affected by anthropogenic noise, given that noise has been demonstrated to impact some crustacean’s ability to detect and respond to chemical, visual, and acoustic cues, all of which are vital in courtship rituals. To explore if noise has an impact on crustacean mating, we tested the responses of male green shore crabs (Carcinus maenas) from the southwest UK coast by exposing them to ship noise recordings while simultaneously presenting them with a dummy-female soaked in the female-sex pheromone uridine diphosphate (UDP) in an experimental tank setup (recording treatment: n = 15, control treatment: n = 15). We found a significant, negative effect of noise on the occurrence of mating behaviour compared to no noise conditions, though no significant effect of noise on the time it took for a crab to respond to the pheromone. Such effects suggest reproductive impairment due to anthropogenic noise, which could potentially contribute to decreased crustacean populations and subsequent ecological and economic repercussions. Given the findings of our preliminary study, more research should be undertaken that includes larger sample sizes, double blind setups, and controlled laboratory trials in order to more fully extrapolate the potential impact of noise on mating in the natural environment.

Effects of pile driving sound playbacks and cadmium co-exposure on the early life stage development of the Norway lobster, Nephrops norvegicus

There is an urgent need to understand how organisms respond to multiple, potentially interacting drivers in today's world. The effects of the pollutants anthropogenic sound (pile driving sound playbacks) and waterborne cadmium were investigated across multiple levels of biology in larval and juvenile Norway lobster, Nephrops norvegicus under controlled laboratory conditions. The combination of pile driving playbacks (170 dB_pk-pk re 1 μPa) and cadmium combined synergistically at concentrations >9.62 μg_[Cd] L^-1 resulting in increased larval mortality, with sound playbacks otherwise being antagonistic to cadmium toxicity. Exposure to 63.52 μg_[Cd] L^-1 caused significant delays in larval development, dropping to 6.48 μg_[Cd] L^-1 in the presence of piling playbacks. Pre-exposure to the combination of piling playbacks and 6.48 μg_[Cd] L^-1 led to significant differences in the swimming behaviour of the first juvenile stage. Biomarker analysis suggested oxidative stress as the mechanism resultant deleterious effects, with cellular metallothionein (MT) being the predominant protective mechanism.

Noisy waters can influence young-of-year lobsters' substrate choice and their antipredatory responses

Offshore human activities lead to increasing amounts of underwater noise in coastal and shelf environments, which may affect commercially-important benthic invertebrate groups like the re-stocked Helgoland European lobster (Homarus gammarus) in the German Bight (North Sea). It is crucial to understand the impact tonal low-frequency noises, like maritime transport and offshore energy operations, may have on substrate choice and lobsters' behavior to assess potential benefits or bottlenecks of new hard-substrate artificial offshore environments that become available. In this study, we investigated the full factorial effect of a tonal low-frequency noise and predator presence on young-of-year (YOY) European lobsters' in a diurnal and nocturnal experiment. Rocks and European oyster shells (Ostrea edulis) were offered as substrate to YOY lobsters for 3 h. Video recordings (n = 134) allowed the identification of lobsters' initial substrate choice, diel activity and key behaviors (peeking, shelter construction, exploration and hiding). To ensure independence, YOY lobsters in the intermolt stage were randomly selected and assigned to the experimental tanks and used only once. We provide the first evidence that stressors alone, and in combination, constrain YOY lobsters' initial substrate choice towards rocks. During nighttime, the joint effect of exposure to a constant low-frequency noise and predator presence decreased antipredator behavior (i.e., hiding) and increased exploration behavior. Noise may thus interfere with YOY lobsters' attention and decision-making processes. This outcome pinpoints that added tonal low-frequency noise in the environment have the potential to influence the behavior of early-life stages of European lobsters under predator pressure and highlights the importance of including key benthic invertebrates' community relationships in anthropogenic noise risk assessments. Among others, effects of noise must be taken into consideration in plans involving the multi-use of any offshore area for decapods' stock enhancement, aquaculture, and temporary no-take zones.

Marine invertebrate anthropogenic noise research - Trends in methods and future directions

Selecting the correct methods to answer one's chosen question is key to conducting rigorous, evidence-based science. A disciplines' chosen methods are constantly evolving to encompass new insights and developments. Analysing these changes can be a useful tool for identifying knowledge gaps and guiding future studies. Research on the impact of anthropogenic noise on marine invertebrates, a topic with specific methodological challenges, has undergone substantial changes since its beginning in 1982. Using this field as an example, we demonstrate the benefits of such method analysis and resulting framework which has the potential to increase conclusive power and comparability of future studies. We list taxa studied to date, use a range of descriptors to analyse the methods applied, and map changes in experimental design through time. Based upon our analysis, three research strategies are proposed as a best practice framework for investigating effects of noise on marine invertebrates and delivering policy-relevant information.

Anthropogenic underwater vibrations are sensed and stressful for the shore crab Carcinus maenas

Acoustic pollution in aquatic environments has increased with adverse effects on many aquatic organisms. However, little work has been done considering the effects of the vibratory component of acoustic stimuli, which can be transmitted in the substrate and propagated into the aquatic medium. Benthic marine organisms, including many invertebrates, are capable of sensing seabed vibration, yet the responses they trigger on organism have received little attention. This study investigates the impact of underwater vibration on the physiology and behaviour of a ubiquitous inhabitant of coastal areas of the northern hemisphere, the shore crab Carcinus maenas. We developed a novel vibratory apparatus with geophones supported on a softly sprung frame to induce a seabed vibration of 20 Hz frequency, as observed during dredging, piling and other anthropogenic activities. The geophone internal mass caused the frame to vibrate in a controlled manner. Our results show that transition from ambient to anthropogenic vibrations induced an increase in activity and antennae beats in shore crabs, indicating perception of the vibratory stimulus and a higher stress level. There was also a trend on sex-specific responses to anthropogenic vibration, with males showing a higher activity level than females. However, no effect of anthropogenic vibrations was found upon oxygen consumption. These results show that anthropogenic underwater vibration induces behavioural responses in Carcinus maenas. This highlights the importance of evaluating man-made vibratory activities on coastal invertebrates and the necessity of evaluating anthropogenic effects on both sexes.

Noise matters: elephants show risk-avoidance behaviour in response to human-generated seismic cues

African elephants (Loxodonta africana) use many sensory modes to gather information about their environment, including the detection of seismic, or ground-based, vibrations. Seismic information is known to include elephant-generated signals, but also potentially encompasses biotic cues that are commonly referred to as ‘noise’. To investigate seismic information transfer in elephants beyond communication, here we tested the hypothesis that wild elephants detect and discriminate between seismic vibrations that differ in their noise types, whether elephant- or human-generated. We played three types of seismic vibrations to elephants: seismic recordings of elephants (elephant-generated), white noise (human-generated) and a combined track (elephant- and human-generated). We found evidence of both detection of seismic noise and discrimination between the two treatments containing human-generated noise. In particular, we found evidence of retreat behaviour, where seismic tracks with human-generated noise caused elephants to move further away from the trial location. We conclude that seismic noise are cues that contain biologically relevant information for elephants that they can associate with risk. This expands our understanding of how elephants use seismic information, with implications for elephant sensory ecology and conservation management.

Substrate vibrations and their potential effects upon fishes and invertebrates

This paper reviews the nature of substrate vibration within aquatic environments where seismic interface waves may travel along the surface of the substrate, generating high levels of particle motion. There are, however, few data on the ambient levels of particle motion close to the seabed and within the substrates of lakes and rivers. Nor is there information on the levels and the characteristics of the particle motion generated by anthropogenic sources in and on the substrate, which may have major effects upon fishes and invertebrates, all of which primarily detect particle motion. We therefore consider how to monitor substrate vibration and describe the information gained from modeling it. Unlike most acoustic modeling, we treat the substrate as a solid. Furthermore, we use a model where the substrate stiffness increases with depth but makes use of a wave that propagates with little or no dispersion. This shows the presence of higher levels of particle motion than those predicted from the acoustic pressures, and we consider the possible effects of substrate vibration upon fishes and invertebrates. We suggest that research is needed to examine the actual nature of substrate vibration and its effects upon aquatic animals.

No negative effects of boat sound playbacks on olfactory-mediated food finding behaviour of shore crabs in a T-maze

Anthropogenic noise underwater is increasingly recognized as a pollutant for marine ecology, as marine life often relies on sound for orientation and communication. However, noise may not only interfere with processes mediated through sound, but also have effects across sensory modalities. To understand the mechanisms of the impact of anthropogenic sound to its full extent, we also need to study cross-sensory interference. To study this, we examined the effect of boat sound playbacks on olfactory-mediated food finding behaviour of shore crabs. We utilized opaque T-mazes with a consistent water flow from both ends towards the starting zone, while one end contained a dead food item. In this way, there were no visual or auditory cues and crabs could only find the food based on olfaction. We did not find an overall effect of boat sound on food finding success, foraging duration or walking distance. However, after excluding deviant data from one out of the six different boat stimuli, we found that crabs were faster to reach the food during boat sound playbacks. These results, with and without the deviant data, seem to contradict an earlier field study in which fewer crabs aggregated around a food source during elevated noise levels. We hypothesise that this difference could be explained by a difference in hunger level, with the current T-maze crabs being hungrier than the free-ranging crabs. Hunger level may affect the motivation to find food and the decision to avoid or take risks, but further research is needed to test this. In conclusion, we did not find unequivocal evidence for a negative impact of boat sound on the processing or use of olfactory cues. Nevertheless, the distinct pattern warrants follow up and calls for even larger replicate samples of acoustic stimuli for noise exposure experiments.

Effect of Covering a Visitor Viewing Area Window on the Behaviour of Zoo-Housed Little Penguins (Eudyptula minor)

Simple Summary

Penguins are a common zoo-housed species and have been shown to display behaviours indicative of fear such as huddling, vigilance and avoidance towards zoo visitors. However, this evidence has been obtained from a single public zoo in Melbourne, Australia. Therefore, we investigated the effect of covering a visitor viewing area window on fear behaviour of zoo-housed little penguins at another zoo in Sydney, Australia. Covering one out of four visitor viewing area windows reduced the number of visitors and the occurrence of potentially threatening visitor behaviours at this window such as banging on the window, loud vocalisations and sudden movement. When the viewing window was covered, the number of penguins visible and preening in the water increased and the number of penguins vigilant near this viewing window reduced. Also, the adjacent corner area, which was not visible to visitors, was found to be a preferred area for the penguins whether the viewing window was uncovered or covered. While there were limited effects, the reduced presence, reduced preening in the water and increased vigilance by penguins near the viewing window when this window was uncovered, together with the general preference for the corner area, provides evidence of some avoidance of visitors. These results suggest that visual contact with visitors and/or other types of visitor contact, such as visitor-induced sounds and vibrations, may be fear-provoking for zoo-housed little penguins. Therefore, these results suggest that penguins in zoos may benefit from modifications to the enclosure that may ameliorate penguin fear responses to visitors such as one-way viewing glass, barriers reducing close visitor contact and areas for penguins to retreat.

Abstract

Studies on the effects of visitors on zoo animals have shown mixed findings and as a result, the manner in which visitors affect zoo animals remains unclear for many species, including a rarely studied taxa such as penguins. Penguins are a common zoo-housed species and have been shown to display huddling, vigilance and avoidance towards zoo visitors which can be indicative of fear. Here, we examined the effects of covering one visitor viewing area window, out of four, on little penguin (Eudyptula minor) behaviours that may be indicative of fear. Two treatments were randomly imposed on different days: (1) The main visitor viewing area window, where most visitor-penguin interactions occurred, was uncovered (‘Main window uncovered’) and (2) The main visitor viewing area window was covered (‘Main window covered’). Penguin numbers and behaviour were recorded near the main visitor viewing area window and the three other visitor viewing area windows, as well as one area not visible to visitors (‘Corner’ area). Furthermore, visitor numbers and visitor behaviour were recorded at all four visitor viewing area windows. Covering the main visitor viewing area window reduced the proportion of visitors present at this window by about 85% (p < 0.001) and reduced potentially threatening visitor behaviours at this window such as tactile contact with the window, loud vocalisations and sudden movement (p < 0.05). When the main visitor viewing area window was covered, the proportion of penguins present increased by about 25% (p < 0.05), the proportion of visible penguins preening in the water increased by about 180% (p < 0.05) and the proportion of visible penguins vigilant decreased by about 70% (p < 0.05) in the area near this main window. A preference for the Corner area was also found whereby 59% and 49% of penguins were present in this area when the main window was uncovered and covered, respectively. These results provide limited evidence that the little penguins in this exhibit showed an aversion to the area near the main visitor viewing area window when it was uncovered based on the increased avoidance and vigilance and decreased preening in the water in this area. This suggests visitors may be fear-provoking for these little penguins. However, it is unclear whether visual contact with visitors per se or other aspects of visitor contact, such as visitor-induced sounds and vibrations, were responsible for this apparent aversion when this window was uncovered.

Taking the Animals' Perspective Regarding Anthropogenic Underwater Sound

Anthropogenic (man-made) sound has the potential to harm marine biota. Increasing concerns about these effects have led to regulation and mitigation, despite there being few data on which to base environmental management, especially for fishes and invertebrates. We argue that regulation and mitigation should always be developed by looking at potential effects from the perspectives of the animals and ecosystems exposed to the sounds. We contend that there is currently a need for far more data on which to base regulation and mitigation, as well as for deciding on future research priorities. This will require a process whereby regulators and researchers come together to identify and implement a strategy that links key scientific and regulatory questions.

First person – Louise Roberts

First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Louise Roberts is first author on ‘Finding a home in the noise: cross-modal impact of anthropogenic vibration on animal search behaviour’, published in BIO. Louise is a Postdoctoral Research Associate in the lab of Mark Laidre at Dartmouth College, USA, investigating how animals interpret their environment using sound in the air and the water, and vibration within sediments and surfaces.

Finding a home in the noise: cross-modal impact of anthropogenic vibration on animal search behaviour

Chemical cues and signals enable animals to sense their surroundings over vast distances and find key resources, like food and shelter. However, the use of chemosensory information may be impaired in aquatic habitats by anthropogenic activities, which produce both water-borne sounds and substrate-borne vibrations, potentially affecting not only vibroacoustic sensing but other modalities as well. We attracted marine hermit crabs (Pagurus acadianus) in field experiments using a chemical cue indicative of a newly available shell home. We then quantified the number of crabs arriving in control versus impulsive noise conditions. Treatment (control or noise), time (before or after), and the interaction between the two significantly affected the numbers of crabs, with fewer crabs attracted to the chemical cue after noise exposure. The results indicate that noise can affect chemical information use in the marine environment, acting cross-modally to impact chemically-guided search behaviour in free-ranging animals. Broadly, anthropogenic noise and seabed vibration may have profound effects, even on behaviours mediated by other sensory modalities. Hence, the impact of noise should be investigated not only within, but also across sensory modalities.

This article has an associated First Person interview with the first author of the paper.

Summary: Chemical cues enable animals to sense their surroundings and find key resources. Here we show that anthropogenic noise affects a chemically-guided search behaviour by acting cross-modally.