What’s all that racket! Soundscapes, phenology, and biodiversity in estuaries

In the southeast USA, significant contributors of biological sound to estuarine ecosystems include snapping shrimp (genus Alpheus and Synalpheus) and soniferous fish (families Batra- choididae and Sciaenidae). Snapping shrimp produce short, broadband calls using their claw, that have been mainly associated with territorial interactions, communication, and foraging. Soniferous fish species including silver perch Bairdiella chrysoura, black drum Pogonias cro- mis, spotted seatrout Cynoscion nebulosus, and red drum Sciaenops ocellatus produce species- specific calls by rapidly moving a pair of sonic muscles against their swim bladder [e.g. 13–17]. Captive studies have shown that calls produced by these fish species are mostly associated with courtship behavior and reproduction [e.g. 16 & 17]. Many sound-producing species use estu- aries periodically for spawning and nurseries, and sound / species richness can vary seasonally [18, 19]. In this study, we deployed three passive acoustic recorders for six years (February 2013— December 2018) in the May River, South Carolina (SC), USA. In addition, we used a catch and release method (i.e. haul seines) to assess species diversity and abundance in intertidal creeks located in close proximity to recording platforms. The specific objectives were to: (i) determine temporal patterns of high, low, and broadband frequency sound pressure levels (SPLs) over the six year time span; (ii) determine how certain environmental factors influence SPLs; (iii) examine phenology of acoustic activity of snapping shrimp and sound producing fish species

(i.e. measured as changes in high and low SPLs, respectively); and (iv) determine temporal pat- terns of species diversity and abundance, and examine how these indices correlate with the soundscape. Results Temporal patterns of the estuarine soundscape Comparisons of high (7,000–40,000 Hz), low (50–1,200 Hz), and broadband (1–40,000 Hz) fre- quency SPLs from 2013 to 2018 revealed temporal and spatial differences (Figs 1 and 2, S1 Fig). Broadband analysis included all physical sounds, biological calls and vocalizations, and anthro- pogenic noise. Low frequency SPLs included fish calls, the lower bandwidth of snapping shrimp snaps, bottlenose dolphin Tursiops truncatus vocalizations (which were few and random), phys- ical sounds, and anthropogenic noise. High frequency SPLs included snapping shrimp snaps, high frequency vocalizations of bottlenose dolphins, physical sounds, and anthropogenic noise. We observed distinct temporal patterns in SPLs that were influenced by location, year, lunar phase, day/night, tidal phase, temperature, day length, and rainfall. From the three ran- dom forest models tested, the models including temperature explained the most variance in the data as compared to models that included rainfall or day length as a factor (S1 and S2 Tables). The designed models with temperature explained 88%, 54%, and 68% of the data vari- ability for high, low, and broadband SPL, respectively (S1 Table). We applied the same models to the data that excluded files with physical sounds and anthropogenic noise (i.e. biological

sounds) for the high, low, and broadband frequency analysis. We observed similar results (i.e. models that included temperature as a factor explained 90%, 56%, and 71% of the data variabil- ity for high, low, and broadband SPL, respectively) (S2 Table). The factors that were most sig- nificant in influencing SPL were location, temperature, and year (S1 and S2 Tables). We observed significant differences in SPL values of biological origin among stations with 14M having the highest values and 9M the lowest (p < 0.05). We detected the highest contribution of anthropogenic noise (i.e. recreational boats) at station 37M (i.e. near the Intracoastal Water- way; 11% of files analyzed) and the lowest at station 9M (i.e. near the headwaters; 2% of files analyzed) (S2–S4 Figs). The anthropogenic noise detected was the most prevalent during the day in the summer months (S2–S4 Figs). PLOS ONE Estuarine soundscapes and biodiversity PLOS ONE | https://doi.org/10.1371/journal.pone.0236874 September 3, 2020 2 / 18 Funding: This work was supported by Spring Island Trust, Town of Bluffton/Beaufort County, multiple University of South Carolina (USC) ASPIRE internal awards, Community Foundation of the Lowcountry, SC EPSCoR/IDeA Program award (#17-RE02), South Carolina Aquarium, Research Initiative for Summer Engagement (RISE) grant from USC, The LowCountry Institute, USCB Sea Islands Institute, Palmetto Bluff Conservancy, and the Port Royal Sound Foundation. This work was also supported, in part, by the Southeast Coastal Ocean Observing Regional Association (SECOORA)

with NOAA financial assistance award number NA16NOS0120028. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of SECOORA or NOAA. All funds were awarded to EWM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.