Oceans have become substantially noisier since the Industrial Revolution. Shipping, resource exploration, and infrastructure development have increased the anthrophony (sounds generated by human activities), whereas the biophony (sounds of biological origin) has been reduced by hunting, fishing, and habitat degradation. Climate change is affecting geophony (abiotic, natural sounds). Existing evidence shows that anthrophony affects marine animals at multiple levels, including their behavior, physiology, and, in extreme cases, survival. This should prompt management actions to deploy existing solutions to reduce noise levels in the ocean, thereby allowing marine animals to reestablish their use of ocean sound as a central ecological trait in a healthy ocean.

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Recent advances in high-resolution ocean circulation models, coupled with a greater understanding of larval behaviour, have increased the sophistication of individual-based, biophysical models used to study the dispersal of larvae in the sea. Fish larvae, in particular, have the ability to swim directionally and increasingly fast during ontogeny, indicating that they may not only disperse, but also migrate using environmental signals. How and when larvae use local and large-scale cues remains a mystery. Including three-dimensional swimming schemes into biophysical models is becoming essential to address these questions. Here, we highlight state-of-the-art modelling of vertical and horizontal migrations of fish larvae, as well as current challenges in moving towards more realistic larval movements in response to cues. Improved understanding of causes for orientation will provide insight into the evolutionary drivers of dispersal strategies for fish and marine organisms in general.

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.

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Numerous animals produce sounds during interactions with potential predators, yet little is known about the acoustics of these sounds, especially in marine environments. California spiny lobsters (Panulirus interruptus) produce pulsatile rasps when interacting with potential predators. They generate sound using frictional structures located at the base of each antenna. This study probes three issues--the effect of body size on signal features, behavioral modification of sound features, and the influence of the ambient environment on the signal. Body size and file length were positively correlated, and larger animals produced lower pulse rate rasps. Ambient noise levels (149.3 dB re 1 microPa) acoustically obscured many rasps (150.4+/-2.0 dB re 1 microPa) at distances from 0.9-1.4 m. Significantly higher numbers of pulses, pulse rate, and rasp duration were produced in rasps generated with two antennae compared to rasps produced with only one antenna. Strong periodic resonances were measured in tank-recorded rasps, whereas field-recorded rasps had little frequency structure. Spiny lobster rasps exhibit flexibility in acoustic signal features, but their propagation is constrained, perhaps beneficially, by the noisy marine environment. Examining the connections between behavior, environment, and acoustics is critical for understanding this fundamental type of animal communication.