The sense of hearing in the Pacific oyster, Magallana gigas

Comparison of the effects of reef and anthropogenic soundscapes on oyster larvae settlement

Settlement is a critical period in the life cycle of marine invertebrates with a planktonic larval stage. For reef-building invertebrates such as oysters and corals, settlement rates are predictive for long-term reef survival. Increasing evidence suggests that marine invertebrates use information from ocean soundscapes to inform settlement decisions. Sessile marine invertebrates with a planktonic stage are particularly reliant on environmental cues to direct them to ideal habitats. As gregarious settlers, oysters prefer to settle amongst members of the same species. It has been hypothesized that oyster larvae from species Crassostrea virginica and Ostrea angasi use distinct conspecific oyster reef sounds to navigate to ideal habitats. In controlled laboratory experiments we exposed Pacific Oyster Magallana gigas larvae to anthropogenic sounds from conspecific oyster reefs, vessels, combined reef-vessel sounds as well as off-reef and no speaker controls. Our findings show that sounds recorded at conspecific reefs induced higher percentages of settlement by about 1.44 and 1.64 times compared to off-reef and no speaker controls, respectively. In contrast, the settlement increase compared to the no speaker control was non-significant for vessel sounds (1.21 fold), combined reef-vessel sounds (1.30 fold), and off-reef sounds (1.18 fold). This study serves as a foundational stepping stone for exploring larval sound feature preferences within this species.

A large-scale experiment finds no consistent evidence of change in mortality or commercial productivity in silverlip pearl oysters (Pinctada maxima) exposed to a seismic source survey

High-intensity, impulsive sounds are used to locate oil and gas reserves during seismic exploration of the seafloor. The impacts of this noise pollution on the health and mortality of marine invertebrates are not well known, including the silverlip pearl oyster (Pinctada maxima), which comprises one of the world's last remaining significant wildstock pearl oyster fisheries, in northwestern Australia. We exposed ≈11,000 P. maxima to a four-day experimental seismic survey, plus one vessel-control day. After exposure, survival rates were monitored throughout a full two-year production cycle, and the number and quality of pearls produced at harvest were assessed. Oysters from two groups, on one sampling day, exhibited reduced survival and pearl productivity compared to controls, but 14 other groups receiving similar or higher exposure levels did not. We therefore found no conclusive evidence of an impact of the seismic source survey on oyster mortality or pearl production.

Daytime boat sound does not affect the behavior of wild thorny oysters (Spondylus americanus): A field-based study

There is increasing awareness of boat sound effects on coral reef assemblages. While behavioral disturbances have been found in fishes, the effects on marine invertebrates remain largely unknown. Here, the behavioral effects of recreational boat sound on thorny oysters at two coral reef habitats within the U.S. Virgin Island National Park were assessed. The "treatment" site was characterized by frequent boat traffic, which increased daytime mean particle acceleration levels (PALrms) by more than 6 dB, while mean PALrms at the "control" site were not contaminated by boat sound. Despite these contrasting soundscapes, all oysters showed the same diurnal cycle, with their valves open at night and partially closed during the day. There was no statistical evidence of behavioral responses in oysters exposed to daytime boat sound. This can be explained by low auditory sensitivity, habituation to a noisy environment due to the pervasiveness of boat sound pollution, or that boat sound may not represent an immediate concern for this species. These findings contrast with laboratory studies that have shown behavioral responses in bivalves exposed to boat sound, highlighting the need for more realistic field-based studies when evaluating potential effects of anthropogenic sounds on this group.

Pile driving and drilling underwater sounds impact the metamorphosis dynamics of Pecten maximus (L., 1758) larvae

One of the biggest challenges of the 21st century is to reduce carbon emissions and offshore wind turbines seem to be an efficient solution. However, during the installation phase, high levels of noise are emitted whose impacts remain not well known, particularly on benthic marine invertebrates displaying a bentho-planktonic life-cycle. For one century, larval settlement and subsequent recruitment has been considered as a key topic in ecology as it determines largely population renewal. Whereas several recent studies have shown that trophic pelagic but also natural soundscape cues could trigger bivalve settlement, the role of anthropogenic noise remains poorly documented. Therefore, we conducted experiments to assess potential interacting effects of diet and pile driving or drilling sounds on the great scallop (Pecten maximus) larval settlement. We demonstrate here that pile driving noise stimulates both growth and metamorphosis as well as it increases the total lipid content of competent larvae. Conversely, drilling noise reduces both survival and metamorphosis rates. For the first time, we provide evidence of noise impacts associated to MREs installation on P. maximus larvae and discuss about potential consequences on their recruitment.

Sound sensitivity of the giant scallop (Placopecten magelanicus) is life stage, intensity, and frequency dependent

There is increasing concern that anthropogenic sounds have a significant impact on marine animals, but there remains insufficient data on sound sensitivities for most invertebrates, despite their ecological and economic importance. We quantified auditory thresholds (in particle acceleration levels) and bandwidth of the giant scallop (Placopecten magellanicus) and subsequently sought to discern sensitivity among two different life stages: juveniles (1 yr olds) and subadults (3 yr olds). We also leveraged a novel valvometry technique to quantify the amplitude of scallop valve gape reductions when exposed to different sound amplitudes and frequencies. Behavioral responses were obtained for lower frequencies below 500 Hz, with best sensitivity at 100 Hz. There were significant differences between the auditory thresholds of juveniles and subadults, with juveniles being more sensitive, suggesting ontogenetic differences in hearing sensitivity. Scallops showed intensity and frequency dependent responses to sounds, with higher valve closures to lower frequencies and higher sound levels. To our knowledge, these are the first data highlighting life stage, intensity, and frequency responses to sound in a marine benthic invertebrate. These results demonstrate clear sound sensitivity and underscore that the potential impacts of anthropogenic sound in valuable ecological resources, such as scallops, may be dependent on sound characteristics.

The nocturnal life of the great scallops (Pecten maximus, L.): First description of their natural daily valve opening cycle

Valvometry techniques used to monitor bivalve gaping activity have elucidated numerous relationships with environmental fluctuations, along with biological rhythms ranging from sub-daily to seasonal. Thus, a precise understanding of the natural activity of bivalves (i.e., not exposed to stressful environmental variations) is necessary as a baseline for detecting abnormal behaviors (deviations). This knowledge is also needed to reliably interpret observations of bivalve gaping behavior and associated biological processes (e.g., respiration, nutrition) acquired over time-limited periods. With this in mind, we investigated the natural daily gaping activity of the great scallop (Pecten maximus) by continuously monitoring 35 individuals in several individual tanks and in situ (Bay of Saint-Brieuc, Brittany, France) using fully autonomous Hall effect sensors. Our results revealed a circadian cycle (τ = 24.0h) in scallop gaping activity. Despite significant inter-individual variability in mean opening and cycle amplitude, almost all individuals (87.5%) exhibited nocturnal activity, with valves more open at night than during the day. A shift in light regime in the tanks triggered an instantaneous change in opening pattern, indicating that light levels strongly determine scallop activity. Based on the opening status of scallops, we also identified several gaping behaviors deviating from the regular daily pattern (lack of rhythmicity, high daytime opening), potentially reflecting physiological weakness. While further long-term studies are required to fully understand the natural activity of scallops, these findings pave the way for studies focused on the scallop response to external factors and introduce further research into the detection of abnormal behaviors. Coupling observations of diel valve gaping cycles with other daily variations in organismal and environmental parameters could help explain mechanisms driving the growth patterns of scallops observed in their shell striations. From a technical perspective, our field-based monitoring demonstrates the suitability of autonomous valvometry sensors for studying mobile subtidal bivalve activity in remote offshore environments.

Multitemporal Scenic Evaluation of Urban Coastal Sites: A Peruvian Case Study

Along the coast of Peru, intensive urbanization and tourism development were related to coastal scenery deterioration. This investigation carried out a scenery evaluation of 20 urban beaches from the “Circuito de Playas de la Costa Verde” (CPCV), a key beach corridor in Lima (Peru). For this purpose, the Coastal Scenic Evaluation System (CSES) was applied in three different seasons, using fuzzy logic to reduce observer subjectivity and estimate the Evaluation index (D). A total of 26 parameters were evaluated to estimate the D value during summer 2020, winter 2020, and summer 2021, to determine the temporal variability of the landscape of an urban coastal sector, such as the CPCV. The results show that all evaluated beaches are classified as very unattractive sites (Class V). Additionally, no significant differences were found between seasons but between beaches. Litter and disturbance factors (noise) were the main human parameters that had low and variable scores during assessments and influenced the D index value estimate. This scenery assessment proposes further implementations of new beach management strategies and actions focusing on landscaping and conserving coastal ecosystems. Strengthening monitoring to reduce noise and litter disturbance and promoting environmentally friendly coastal usage are vital aspects that must be implemented.

Soundscapes as heard by invertebrates and fishes: Particle motion measurements on coral reefs

Coral reef soundscapes are increasingly studied for their ecological uses by invertebrates and fishes, for monitoring habitat quality, and to investigate effects of anthropogenic noise pollution. Few examinations of aquatic soundscapes have reported particle motion levels and variability, despite their relevance to invertebrates and fishes. In this study, ambient particle acceleration was quantified from orthogonal hydrophone arrays over several months at four coral reef sites, which varied in benthic habitat and fish communities. Time-averaged particle acceleration magnitudes were similar across axes, within 3 dB. Temporal trends of particle acceleration corresponded with those of sound pressure, and the strength of diel trends in both metrics significantly correlated with percent coral cover. Higher magnitude particle accelerations diverged further from pressure values, potentially representing sounds recorded in the near field. Particle acceleration levels were also reported for boat and example fish sounds. Comparisons with particle acceleration derived audiograms suggest the greatest capacity of invertebrates and fishes to detect soundscape components below 100 Hz, and poorer detectability of soundscapes by invertebrates compared to fishes. Based on these results, research foci are discussed for which reporting of particle motion is essential, versus those for which sound pressure may suffice.

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.

Repairing recruitment processes with sound technology to accelerate habitat restoration

Humanity's ambitions to revive ecosystems at large scales require solutions to move restoration efforts beyond the small scale. There are increasing calls for technological solutions to reduce costs and facilitate large-scale restoration through the use of emerging technologies using an adaptive process of research and development. We show how technological enrichment of marine soundscapes may provide a solution that repairs the recruitment process to accelerate the recovery of lost marine habitats. This solution would solve the problems of current practice that largely relies upon natural recruitment processes, which carries considerable risk where recruitment is variable or eroded. By combining the literature with laboratory experiments, we describe evidence for "highways of sound" that convey navigable information for dispersing life stages in search for adult habitat. We show that these navigational cues tend to be silenced as their habitat is lost, creating negative feedbacks that hinders restoration. We suggest that reprovisioning soundscapes using underwater technology offers the potential to reverse this feedback and entice target organisms to recruit in greater densities. Collective evidence indicates that the application of soundscape theory and technology may unlock the recruitment potential needed to trigger the recruitment of target organisms and the natural soundscapes they create at large scales.

Regulatory Role of Sugars on the Settlement Inducing Activity of a Conspecific Cue in Pacific Oyster Crassostrea gigas

This study evaluated the larval settlement inducing effect of sugars and a conspecific cue from adult shell extract of Crassostrea gigas. To understand how the presence of different chemical cues regulate settlement behavior, oyster larvae were exposed to 12 types of sugars, shell extract-coated and non-coated surfaces, and under varied sugar exposure times. Lectin-glycan interaction effects on settlement and its localization on oyster larval tissues were investigated. The results showed that the conspecific cue elicited a positive concentration dependent settlement inducing trend. Sugars in the absence of a conspecific cue, C. gigas adult shell extract, did not promote settlement. Whereas, in the presence of the cue, showed varied effects, most of which were found inhibitory at different concentrations. Sugar treated larvae exposed for 2 h showed significant settlement inhibition in the presence of a conspecific cue. Neu5Ac, as well as GlcNAc sugars, showed a similar interaction trend with wheat germ agglutinin (WGA) lectin. WGA-FITC conjugate showed positive binding on the foot, velum, and mantle when exposed to GlcNAc sugars. This study suggests that a WGA lectin-like receptor and its endogenous ligand are both found in the larval chemoreceptors and the shell Ethylenediaminetetraacetic acid (EDTA) extract that may complementarily work together to allow the oyster larva greater selectivity during site selection.

Evolutionary responses of marine organisms to urbanized seascapes

Many of the world's major cities are located in coastal zones, resulting in urban and industrial impacts on adjacent marine ecosystems. These pressures, which include pollutants, sewage, runoff and debris, temperature increases, hardened shorelines/structures, and light and acoustic pollution, have resulted in new evolutionary landscapes for coastal marine organisms. Marine environmental changes influenced by urbanization may create new selective regimes or may influence neutral evolution via impacts on gene flow or partitioning of genetic diversity across seascapes. While some urban selective pressures, such as hardened surfaces, are similar to those experienced by terrestrial species, others, such as oxidative stress, are specific to aquatic environments. Moreover, spatial and temporal scales of evolutionary responses may differ in the ocean due to the spatial extent of selective pressures and greater capacity for dispersal/gene flow. Here, we present a conceptual framework and synthesis of current research on evolutionary responses of marine organisms to urban pressures. We review urban impacts on genetic diversity and gene flow and examine evidence that marine species are adapting, or are predicted to adapt, to urbanization over rapid evolutionary time frames. Our findings indicate that in the majority of studies, urban stressors are correlated with reduced genetic diversity. Genetic structure is often increased in urbanized settings, but artificial structures can also act as stepping stones for some hard-surface specialists, promoting range expansion. Most evidence for rapid adaptation to urban stressors comes from studies of heritable tolerance to pollutants in a relatively small number of species; however, the majority of marine ecotoxicology studies do not test directly for heritability. Finally, we highlight current gaps in our understanding of evolutionary processes in marine urban environments and present a framework for future research to address these gaps.

Asiatic clam Corbicula fluminea exhibits distinguishable behavioural responses to crude oil under semi-natural multiple stress conditions

Aquatic ecosystems are subject to many anthropogenic disturbances, and understanding their possible impacts is a real challenge. Developing approaches based on the behaviour of bivalve mollusks, an integrating marker of the state of the organisms, and therefore of their environment, is relevant, whether within a natural ecosystem or an ecosystem subject to industrial activities. The main objective of this study was to identify by HFNI Valvometry a reliable and reproducible clam behavioural response in the presence of crude oil in a multistress context. To closely replicate actual field conditions, Corbicula fluminea was exposed in outdoor artificial streams that were subject to natural variations and were continuously fed by fresh water from the Gave de Pau (S.W. France). After a period of 26 days in these artificial streams, the clams (n = 14-16 per condition) were separately exposed for 10 days to crude oil alone, crude oil and barium, crude oil and noise pollution, crude oil and turbidity pulses, barium alone, noise pollution alone, turbidity pulses alone or natural changes alone. The secondary objective was to characterize the accumulation of polycyclic aromatic hydrocarbons (PAH) in 3 tissues (gills, adductor muscles and foot) in clams exposed for 10 days to crude oil alone or under multistress conditions (n = 5 clams per condition) and then to compare the accumulation and behaviour of clams under these conditions. The response of clams to crude oil alone or under multistress conditions was visually and statistically significant and not confounded by the other disturbances tested, despite large variations in water temperature. In the presence of crude oil, the behaviour of clams was characterized by an increase in valve-closure duration, a decrease in valve-opening amplitude and an increase in valve agitation index. In the presence of crude oil, the clam behaviour showed no direct relationship with PAH accumulation in the gills, adductor muscles or foot, although hypothetical mechanisms are discussed. This work supports the growing interest in studying the behaviour of bivalve mollusks in the context of biomonitoring of the aquatic environment surrounding oil facilities.

Waves cue distinct behaviors and differentiate transport of congeneric snail larvae from sheltered versus wavy habitats

Marine population dynamics often depend on dispersal of larvae with infinitesimal odds of survival, creating selective pressure for larval behaviors that enhance transport to suitable habitats. One intriguing possibility is that larvae navigate using physical signals dominating their natal environments. We tested whether flow-induced larval behaviors vary with adults' physical environments, using congeneric snail larvae from the wavy continental shelf (Tritia trivittata) and from turbulent inlets (Tritia obsoleta). Turbulence and flow rotation (vorticity) induced both species to swim more energetically and descend more frequently. Accelerations, the strongest signal from waves, induced a dramatic response in T. trivittata but almost no response in competent T. obsoleta Early stage T. obsoleta did react to accelerations, ruling out differences in sensory capacities. Larvae likely distinguished turbulent vortices from wave oscillations using statocysts. Statocysts' ability to sense acceleration would also enable detection of low-frequency sound from wind and waves. T. trivittata potentially hear and react to waves that provide a clear signal over the continental shelf, whereas T. obsoleta effectively "go deaf" to wave motions that are weak in inlets. Their contrasting responses to waves would cause these larvae to move in opposite directions in the water columns of their respective adult habitats. Simulations showed that the congeners' transport patterns would diverge over the shelf, potentially reinforcing the separate biogeographic ranges of these otherwise similar species. Responses to turbulence could enhance settlement but are unlikely to aid large-scale navigation, whereas shelf species' responses to waves may aid retention over the shelf via Stokes drift.

Noise pollution limits metal bioaccumulation and growth rate in a filter feeder, the Pacific oyster Magallana gigas

Shipping has increased dramatically in recent decades and oysters can hear them. We studied the interaction between noise pollution and trace metal contamination in the oyster Magallana gigas. Four oyster-groups were studied during a 14-day exposure period. Two were exposed to cadmium in the presence of cargo ship-noise ([Cd⁺⁺]w ≈ 0.5 μg∙L^-1; maximum sound pressure level 150 dBrms re 1 μPa), and 2 were exposed only to cadmium. The Cd concentration in the gills ([Cd]g) and the digestive gland ([Cd]dg), the valve closure duration, number of valve closures and circadian distribution of opening and closure, the daily shell growth-rate and the expression of 19 genes in the gills were studied. Oysters exposed to Cd in the presence of cargo ship-noise accumulated 2.5 times less Cd in their gills than did the controls without ship noise and their growth rate was 2.6 times slower. In the presence of ship noise, oysters were closed more during the daytime, and their daily valve activity was reduced. Changes in gene activity in the gills were observed in 7 genes when the Cd was associated with the ship noise. In the absence of ship noise, a change in expression was measured in 4 genes. We conclude that chronic exposure to cargo ship noise has a depressant effect on the activity in oysters, including on the volume of the water flowing over their gills (Vw). In turn, a decrease in the Vw and valve-opening duration limited metal exposure and uptake by the gills but also limited food uptake. This latter conclusion would explain the slowing observed in the fat metabolism and growth rate. Thus, we propose that cargo ship noise exposure could protect against metal bioaccumulation and affect the growth rate. This latter conclusion points towards a potential risk in terms of ecosystem productivity.

A Rhodopsin-Like Gene May Be Associated With the Light-Sensitivity of Adult Pacific Oyster Crassostrea gigas

Light-sensitivity is important for mollusc survival, as it plays a vital role in reproduction and predator avoidance. Light-sensitivity has been demonstrated in the adult Pacific oyster Crassostrea gigas, but the genes associated with light-sensitivity remain unclear. In the present study, we designed experiments to identify the genes associated with light-sensitivity in adult oysters. First, we assessed the Pacific oyster genome and identified 368 genes annotated with the terms associated with light-sensitivity. Second, the function of the four rhodopsin-like superfamily member genes was tested by using RNAi. The results showed that the highest level of mRNA expression of the vision-related genes was in the mantle; however, this finding is not true for all oyster genes. Interestingly, we also found four rhodopsin-like superfamily member genes expressed at an very high level in the mantle tissue. In the RNAi experiment, when one of rhodopsin-like superfamily member genes (CGI_1001253) was inhibited, the light-sensitivity capacity of the injected oysters was significantly reduced, suggesting that CGI_10012534 may be associated with light-sensitivity in the adult Pacific oyster.