Exposure to boat noise in the field yields minimal stress response in wild reef fish

Aquatic anthropogenic noise is on the rise, with growing concern about its impact on species that are sensitive to low-frequency sounds (e.g. most fish and invertebrates). We investigated whether the reef fish Halichoeres bivittatus living in both noisy and quiet areas had differing levels of baseline stress (measured as whole-body cortisol) and whether they would exhibit a physiological stress response when exposed to boat noise playbacks. While the playback experiments significantly increased cortisol levels in fish from our experiment compared to baseline levels, there were minimal pairwise differences across treatments and no difference in baseline stress for fish living in noisy vs. quiet areas. These results may be explained by low overall auditory sensitivity, habituation to a fairly noisy environment (due to biological sounds), or that boat noise simply may not represent an immediate threat to survival in this species. These findings contrast recent studies that have shown elevated stress responses in fishes when exposed to boat noise and highlights that inter-specific differences must be considered when evaluating potential impacts of anthropogenic noise on marine life

It\u27s Time to Listen: There is Much to be Learned from the Sounds of Tropical Ecosystems

Knowledge that can be gained from acoustic data collection in tropical ecosystems is low‐hanging fruit. There is every reason to record and with every day, there are fewer excuses not to do it. In recent years, the cost of acoustic recorders has decreased substantially (some can be purchased for under US$50, e.g., Hill et al. 2018) and the technology needed to store and analyze acoustic data is continuously improving (e.g., Corrada Bravo et al. 2017, Xie et al. 2017). Soundscape recordings provide a permanent record of a site at a given time and contain a wealth of invaluable and irreplaceable information. Although challenges remain, failure to collect acoustic data now in tropical ecosystems would represent a failure to future generations of tropical researchers and the citizens that benefit from ecological research. In this commentary, we (1) argue for the need to increase acoustic monitoring in tropical systems; (2) describe the types of research questions and conservation issues that can be addressed with passive acoustic monitoring (PAM) using both short‐ and long‐term data in terrestrial and freshwater habitats; and (3) present an initial plan for establishing a global repository of tropical recordings

The sound of communication in underwater acoustic sensor networks: (Position paper)

Underwater environments have never been much of a constraint to the rich animal life they support at all depths of our seas and oceans. Indeed, nature has taken advantage of this environment to develop a rich variety of efficient communication strategies through evolutionary change and adaptation. The wealth of knowledge to be discovered will continue to dazzle and fascinate the world. For underwater sensor network communication, acoustic signalling is the preferred choice for designers because sound propagation is the most efficient when compared to other forms, like thermal, light, and electromagnetic. It is within this acoustic environment that researchers have to innovate and develop new ideas and methodologies so as to advance the state-of-the-art. In this paper, several fundamental issues and connections are discussed that arise in the study of underwater wireless sensor networks. A variety of ideas and solutions for further research is proposed and fundamental issues in topology control, directional underwater transducers, and monitoring and surveillance are disc

Response of gilthead seabream (Sparus aurata L., 1758) larvae to nursery odor cues as described by a new set of behavioral indexes

Temperate marine fish larvae use a series of environmental cues (e.g., olfactory, hearing, visual) to mediate the selection of nursery habitats. However, habitat selection may vary according to individuals' physiological condition. Therefore, this study aimed to determine the ability of gilthead seabream (Sparus aurata L., 1758) larvae to utilize natural odor cues to locate nursery habitats along ontogeny and to examine how it varies with individual's physiological condition. The hypothesis being tested is that S. aurata larvae prefer coastal rocky reefs as nursery areas, but they might use coastal lagoons as nursery grounds—ecosystems known for their productivity—if under starvation conditions, as a compensatory mechanism to avoid slow growth or even death. A choice-chamber experiment was used to investigate the behavioral responses of satiated and starved laboratory-reared S. aurata larvae, along ontogeny (pre-flexion, flexion, post-flexion), to water collected in a coastal artificial rocky reef and a coastal lagoon. The physiological condition of S. aurata larvae was determined by analyzing several biochemical condition indices. Complementarily, a new set of four preference indexes were developed—Choice-Chamber Preference Indexes—and discussed to provide a clear measure of the behavioral changes of a species along ontogeny by balancing all the behavioral choices made during the experimental trials, including the unresponsive behavior. A developmental threshold was identified at 24 days post-hatching, before which insufficient swimming capability disabled responsive behavior. Beyond this threshold, post-flexion larvae preferred rocky coastal water over lagoon water, even if under starvation conditions or poor physiological condition, despite the fact that the unresponsive behavior was largely predominant. S. aurata larvae displayed a cautionary behavioral strategy, so the compensatory mechanisms to ensure metapopulation stability and resilience have to rely on their feeding plasticity and on being a batch-spawning species (i.e., diversified bet-hedging strategy) to compensate the lack of apparent behavioral plasticity.info:eu-repo/semantics/publishedVersio

Exposure to boat noise in the field yields minimal stress response in wild reef fish

Aquatic anthropogenic noise is on the rise, with growing concern about its impact on species that are sensitive to low-frequency sounds (e.g. most fish and invertebrates). We investigated whether the reef fish Halichoeres bivittatus living in both noisy and quiet areas had differing levels of baseline stress (measured as whole-body cortisol) and whether they would exhibit a physiological stress response when exposed to boat noise playbacks. While the playback experiments significantly increased cortisol levels in fish from our experiment compared to baseline levels, there were minimal pairwise differences across treatments and no difference in baseline stress for fish living in noisy vs. quiet areas. These results may be explained by low overall auditory sensitivity, habituation to a fairly noisy environment (due to biological sounds), or that boat noise simply may not represent an immediate threat to survival in this species. These findings contrast recent studies that have shown elevated stress responses in fishes when exposed to boat noise and highlights that inter-specific differences must be considered when evaluating potential impacts of anthropogenic noise on marine life

Temporal and Spatial Patterns in Coral Reef Soundscapes and their Relevance for Larval Fish Orientation

Most coral reef fish adults have limited home ranges, but their pelagic larvae have the potential to disperse over great distances. At the end of the pelagic phase, these larvae must seek appropriate settlement habitat. Which environmental signals do they use to find the reef? It has been suggested that fish larvae utilize a combination of visual, olfactory, and acoustic cues at different ontogenetic stages and different distances from the reef. At least ten experiments in the last decade have tested the response of reef fish larvae to sounds of a coral reef, resulting in more than 650 citations. This dissertation focuses on the potential role of acoustic cues in the orientation behavior of larval reef fish from the open ocean. First, a biophysical model was used to examine the consequences of orientation behavior if larvae could detect acoustic signals from 1-10 km from the reef. When larvae oriented early during ontogeny and from larger distances, they greatly increased their settlement success and settled closer to home. These findings suggest that early orientation is critical to the survival of fish larvae, which must be active agents of their own dispersal. Second, a time-series of coral reef soundscapes was conducted for two nearby coral reefs in the Northern Florida Keys. The reef soundscapes were highly variable over daily, lunar, and seasonal time-scales, and the highest amplitudes coincided with new moons of the wet season - the time when the larvae of most coral reef fish species settle. Interestingly, the wind-based contribution to the soundscape also had a lunar period. Third, an acoustic playback experiment was conducted at Dean’s Blue Hole in the Bahamas, a relatively “quiet” environment. Larvae from Apogonidae (cardinalfish) and Acanthuridae (surgeonfish) families were exposed to reef sounds recorded in the Bahamas and in Florida and played back at ambient levels. The acanthurid species demonstrated no response to the playbacks, but the apogonids exhibited a disruption of their orientation behavior. This finding suggests that apogonids were able to detect the playbacks, but had no directional response, as was anticipated based on previous studies where sounds were broadcast at higher amplitudes. Finally, an acoustic propagation experiment was conducted in the Upper Florida Keys. Both acoustic pressure and particle acceleration diminished gradually with distance from the reef, but the amplitude of the signal, particularly for particle acceleration, was lower than the detection thresholds of most fish larvae. Furthermore, the particle acceleration field (measured 1-1000 m from the reef) was not highly directional, which may restrict the use of acoustic signals to animals that can detect acoustic pressure. These findings suggest that most fish larvae in the pelagic zone near Florida reefs would have a difficult time locating the reef using acoustic cues alone. However, this may not be the case for species with particularly sensitive hearing (e.g., those that can detect acoustic pressure), and for reefs with higher-amplitude soundscapes. The results of this study challenge research from the past decades that demonstrated a clear attraction of larval fishes to sounds played-back at high amplitudes. Further work is needed, specifically hearing thresholds in other fish larvae, and particle acceleration measurements over longer time periods and near additional coral reefs, to determine whether the trends found in the Florida Keys are consistent with other parts of the world