Keeping track of long-term biological trends in many marine habitats is a challenging task that is exacerbated when the habitats in question are in remote locations. Monitoring the ambient sound field may be a useful way of assessing biological activity because many behavioral processes are accompanied by sound production. This article reports the preliminary results of an effort to develop and use an Ecological Acoustic Recorder (EAR) to monitor biological activity on coral reefs and in surrounding waters for periods of 1 year or longer. The EAR is a microprocessor-based autonomous recorder that periodically samples the ambient sound field and also automatically detects sounds that meet specific criteria. The system was used to record the sound field of coral reefs and other marine habitats on Oahu, HI. Snapping shrimp produced the dominant acoustic energy on the reefs examined and exhibited clear diel acoustic trends. Other biological sounds recorded included those produced by fish and cetaceans, which also exhibited distinct temporal variability. Motor vessel activity could also be monitored effectively with the EAR. The results indicate that acoustic monitoring may be an effective means of tracking biological and anthropogenic activity at locations where continuous monitoring by traditional survey methods is impractical.

SUMMARYAlthough hearing has been described for many underwater species, there is much debate regarding if and how cephalopods detect sound. Here we quantify the acoustic sensitivity of the longfin squid (Loligo pealeii) using near-field acoustic and shakergenerated acceleration stimuli. Sound field pressure and particle motion components were measured from 30 to 10,000Hz and acceleration stimuli were measured from 20 to 1000Hz. Responses were determined using auditory evoked potentials (AEPs) with electrodes placed near the statocysts. Evoked potentials were generated by both stimuli and consisted of two wave types: (1) rapid stimulus-following waves, and (2) slower, high-amplitude waves, similar to some fish AEPs. Responses were obtained between 30 and 500Hz with lowest thresholds between 100 and 200Hz. At the best frequencies, AEP amplitudes were often >20V. Evoked potentials were extinguished at all frequencies if (1) water temperatures were less than 8°C, (2) statocysts were ablated, or (3) recording electrodes were placed in locations other than near the statocysts. Both the AEP response characteristics and the range of responses suggest that squid detect sound similarly to most fish, with the statocyst acting as an accelerometer through which squid detect the particle motion component of a sound field. The modality and frequency range indicate that squid probably detect acoustic particle motion stimuli from both predators and prey as well as low-frequency environmental sound signatures that may aid navigation. Supplementary material available online at

Ecosystems and the communities they support are changing at alarmingly rapid rates. Tracking species diversity is vital to managing these stressed habitats. Yet, quantifying and monitoring biodiversity is often challenging, especially in ocean habitats. Given that many animals make sounds, these cues travel efficiently under water, and emerging technologies are increasingly cost-effective, passive acoustics (a long-standing ocean observation method) is now a potential means of quantifying and monitoring marine biodiversity. Properly applying acoustics for biodiversity assessments is vital. Our goal here is to provide a timely consideration of emerging methods using passive acoustics to measure marine biodiversity. We provide a summary of the brief history of using passive acoustics to assess marine biodiversity and community structure, a critical assessment of the challenges faced, and outline recommended practices and considerations for acoustic biodiversity measurements. We focused on temperate and tropical seas, where much of the acoustic biodiversity work has been conducted. Overall, we suggest a cautious approach to applying current acoustic indices to assess marine biodiversity. Key needs are preliminary data and sampling sufficiently to capture the patterns and variability of a habitat. Yet with new analytical tools including source separation and supervised machine learning, there is substantial promise in marine acoustic diversity assessment methods.

12Coral reefs provide a wide array of ecosystem services and harbor some of the highest levels of