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

Anthropogenic carbon dioxide (CO2) is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form aragonite cuttlebones and statoliths, are of concern because of the central role they play in many ocean ecosystems and because of their importance to global fisheries. Atlantic longfin squid (Doryteuthis pealeii), an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae) under ambient and elevated CO2 concentrations in replicated experimental trials. Animals raised under elevated pCO2 demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO2-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.

Pop-up satellite archival transmitting (PSAT) tags are capable of storing high-resolution behavioral and environmental information for extended periods of time (approximately 1 year), rendering them especially valuable for studying highly mobile species. In this review, we synthesize published PSAT data to understand the biophysical drivers that influence movements of billfishes (families Xiphiidae and Istiophoridae). To date, over 1,080 PSATs have been deployed on billfishes, with individuals demonstrating both trans-equatorial and trans-basin movements. Using this dataset, we identify four main physical variables that drive billfish behavior: temperature, light, oxygen, and complex water mixing (e.g. fronts and eddies). Of the seven species that have been studied with PSAT technology, all exhibited a strong thermal preference for water >22°C, though vertically migrating swordfish additionally occupied waters <10°C while at depth. Ambient light levels influence vertical movements, especially those associated with foraging, as billfish possess large eyes and thermoregulatory abilities that facilitate feeding behaviors below warm surface layers. Mounting evidence suggests that some billfishes actively avoid regions with low dissolved oxygen (<3.5 mL L −1). Human-induced climate change is expected to increase the horizontal and vertical extent of hypoxic water and may further compress habitat and concentrate fishing pressure on pelagic fishes. Finally, complex submeso-and mesoscale processes provide critical habitat for spawning, larval feeding, and retention, but our understanding of these and other behavioral aspects of billfish biology remains limited. Future research efforts should leverage technical advancements while integrating existing and future tag data with chemical and physical oceanographic datasets to gain a better understanding of the relevant biophysical interactions for billfishes, thereby enhancing management capabilities for this ecologically and economically important group of fishes.

13Coral reefs are characterized by high biodiversity and evidence suggests that reef soundscapes 14 reflect local species assemblages. To investigate how sounds produced on a given reef relate to 15 abiotic and biotic parameters and how that relationship may change over time, an observational 16 study was conducted between September 2014 and January 2016 at seven Hawaiian reefs that 17 varied in coral cover, rugosity, and fish assemblages. The reefs were equipped with temperature 18 loggers and acoustic recording devices that recorded on a 10% duty cycle. Benthic and fish 19 visual survey data were collected four times over the course of the study. On average, reefs 20 ranged from 0 to 80% live coral cover, although changes between surveys were noted, in 21 particular during the major El Niño-related bleaching event of October 2015. Acoustic analyses 22 focused on two frequency bands (50-1200 Hz and 1.8-20.5 kHz) that corresponded to the 23 dominant spectral features of the major sound-producing taxa on these reefs, fish and snapping 24 shrimp, respectively. In the low-frequency band, the presence of humpback whales (December-25 May) was a major contributor to sound level, whereas in the high-frequency band sound level 26 closely tracked water temperature. On shorter timescales, the magnitude of the diel trend in 27 sound production was greater than that of the lunar trend, but both varied in strength among 28 reefs, which may reflect differences in the species assemblages present. Results indicated that the 29 magnitude of the diel trend was related to fish densities at low frequencies and coral cover at 30 high frequencies; however, the strength of these relationships varied by season. Thus, long-term 31 acoustic recordings capture the substantial acoustic variability present in coral-reef ecosystems 32 and provide insight into the presence and relative abundance of sound-producing organisms. 33 34

Approximately half of the North Pacific humpback whale Megaptera novaeangliae stock visits the shallow waters of the main Hawaiian Islands seasonally. Within this breeding area, mature males produce an elaborate acoustic display known as song, which becomes the dominant source of ambient underwater sound between December and April. Following reports of unusually low whale numbers that began in 2015/16, we examined song chorusing recorded through long-term passive acoustic monitoring at 6 sites off Maui as a proxy for relative whale abundance between 2014 and 2019. Daily root-mean-square sound pressure levels (RMS SPLs) were calculated to compare variations in low-frequency acoustic energy (0-1.5 kHz). After 2014/15, the overall RMS SPLs decreased between 5.6 and 9.7 dB re 1 µPa2 during the peak of whale season (February and March), reducing ambient acoustic energy from chorusing by over 50%. This change in song levels co-occurred with a broad-scale oceanic heat wave in the northeast Pacific termed the ‘Blob,’ a major El Niño event in the North Pacific, and a warming period in the Pacific Decadal Oscillation cycle. Although it remains unclear whether our observations reflect a decrease in population size, a change in migration patterns, a shift in distribution to other areas, a change in the behavior of males, or some combination of these, our results indicate that continued monitoring and further studies of humpback whales throughout the North Pacific are warranted to better understand the fluctuations occurring in this recently recovered population and other populations that continue to be endangered or threatened.

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Human activity is contributing increasing noise to marine ecosystems. Recent studies have examined the effects of boat noise on marine fishes, but there is limited understanding of the prevalence of this sound source. This investigation tracks vessel noise on three reefs in the US Virgin Islands National Park over four months in 2013. Ambient noise levels ranged from 106-129 dB rms re 1 µPa (100 Hz -20 kHz). Boat noise occurred in 6-12% of samples. In the presence of boat noise, ambient noise in a low-frequency band (100-1000 Hz) increased by >7 dB above baseline levels and sound levels were significantly higher. The frequency with the most acoustic energy shifted to a significantly lower frequency when boat noise was present during the day.These results indicate the prevalence of boat noise and its overlap with reef organism sound production, raising concern for the communication abilities of these animals.

Biological sounds produced on coral reefs may provide settlement cues to marine larvae. Sound fields are composed of pressure and particle motion, which is the back and forth movement of acoustic particles. Particle motion (i.e., not pressure) is the relevant acoustic stimulus for many, if not most, marine animals. However, there have been no field measurements of reef particle motion. To address this deficiency, both pressure and particle motion were recorded at a range of distances from one Hawaiian coral reef at dawn and mid-morning on three separate days. Sound pressure attenuated with distance from the reef at dawn. Similar trends were apparent for particle velocity but with considerable variability. In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef.