Linking spatiotemporal variability in sound signatures to coral reef species assemblages

Maxwell Kaplan, Biology
Advisor: Aran Mooney, Biology

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Research Summary

Coral reefs are in global decline as a result of multiple stressors. Many of the animals that inhabit coral reefs produce sound; recording reef sounds appears to be a promising way to track and monitor ecosystem health and the diversity of life on reefs. I am currently collecting acoustic recordings on eight reefs on Maui’s coast. The objective is to link the sounds recorded to the species assemblages present on each reef. Visual surveys for fish and benthic cover are carried out whenever recorders are deployed and recovered. The acoustic recorders are due to be collected in January 2016. While funding is currently available to cover travel to Maui for a related project, there is currently no available funding to support SCUBA operations, diving support, and a final round of visual surveys. However, there is an urgent need to carry out another set of visual surveys as a result of the projected major bleaching event this fall. Thus, I am requesting funding to support this final round of visual surveys, which will provide a major complement to this dataset.
 
Introduction
Many coral reef ecosystems support high biodiversity and provide key habitat for several taxa (Graham & Nash 2013) as well as valuable ecosystem services (Graham et al. 2013). However, reefs are in decline worldwide as a result of multiple stressors (Bellwood et al. 2004, De'ath et al. 2012). Monitoring changes in these valuable ecosystems is a high priority, but traditional monitoring approaches can be intermittent and costly (Lammers et al. 2008). Biological sounds in the sea are utilized by a diverse array of organisms and can play a vital role in the functioning of marine communities. This is because sound production is an important component of a number of biological processes such as spawning, courtship, and aggressive displays. Recording these sounds can reveal the occurrence of these behaviors, which are otherwise difficult to observe. Sounds can also be used to indicate the presence of certain taxa (e.g. Mann et al. 2009). Unlike visual surveys, acoustic recordings can be collected without human presence, at night, and over long periods of time.
A pilot study that I conducted in the U.S. Virgin Islands National Park found links between coral cover, fish density, and the strength of a diel trend in sound production in a low frequency band dominated by fish calling activity (Kaplan et al. 2015). In an attempt to build on that study I started a collaborative project with the Oceanwide Science Institute in Maui, Hawaii, in September 2014, in which eight reefs were instrumented with acoustic recorders, thereby expanding the pilot work to include a larger number of sites that varied considerably in their benthic cover and fish species assemblages.
Instruments are currently deployed on 8 reefs on Maui and are due to be collected in January 2016, which will yield 15 months of nearly continuous acoustic data collection. However, there is an urgent need to carry out another set of visual surveys as a result of a projected major bleaching event this fall, in order to link any changes we see in the soundscape to changes in fish diversity and density and benthic cover. Currently, funding exists for travel to the study site as part of another related project studying humpback whale sound production and acoustic particle motion. This proposal details a request for funding to support diving operations, additional vessel fuel to reach the study sites, and for SCUBA diving personnel support, all of which are currently unfunded.
 
Objectives
1. Carry out a final round of visual assessments of benthic cover, reef rugosity, and fish abundance and diversity.
2. Analyze the acoustic records in the context of habitat quality (benthic cover, architectural complexity, fish species richness and abundance) and abiotic factors (wind and wave exposure, depth, and temperature) to assess links between species assemblages, reef soundscapes, and environmental disturbances (e.g. bleaching).
 
Approach
Acoustic recording devices deployed on eight reefs in Maui have already recorded for approximately nine months and have been refurbished to support further data collection until January 2016, at which time they are due to be retrieved. Acoustic analyses include removing periods of vessel and other noise and correcting for recording hydrophone sensitivity. Root-mean-square energy will be calculated in two frequency bands – low (100-1000 Hz) and high (2-20 kHz) – for fish and snapping shrimp, respectively, in order to identify diel trends in sound production at each site over the recording period. Spectral analysis will be used to better elucidate the temporal periodicity of these trends (i.e., diel, lunar, seasonal scales) in methods similar to those used by Kaplan et al. (2015).
Visual survey data will be analyzed to determine how species assemblages have changed over the study period and to what extent any of these changes correlate with environmental parameters (e.g. temperature, storms, etc.) or the acoustic records.
 
Broader Impacts
Leveraging knowledge gained during my pilot investigation of coral reef acoustics in the U.S. Virgin Islands (Kaplan et al. 2015), this study will assess the links between coral reef habitat quality, level of protection, species present, and biological sound production. Additional visual surveys are needed and timely because of the predicted major bleaching event that is expected to occur in Hawaii this fall and will greatly enhance the value of this already substantial dataset. The results of this investigation will be presented at the next International Coral Reef Symposium in 2016. Data from this investigation will also be published in a peer-reviewed journal and will form a chapter of my PhD dissertation. Funding support will be acknowledged in all conference proceedings and publications.
 
References
Bellwood DR, Hughes TP, Folke C, Nystrom M (2004) Confronting the coral reef crisis. Nature 429:827-833
De'ath G, Fabricius KE, Sweatman H, Puotinen M (2012) The 27-year decline of coral cover on the Great Barrier Reef and its causes. Proc Natl Acad Sci U S A 109:17995-17999
Graham NA, Bellwood DR, Cinner JE, Hughes TP, Norstrom AV, Nystrom M (2013) Managing resilience to reverse phase shifts in coral reefs. Front Ecol Environ 11:541-548
Graham NAJ, Nash KL (2013) The importance of structural complexity in coral reef ecosystems. Coral Reefs 32:315-326
Kaplan MB, Mooney TA, Partan J, Solow AR (2015) Coral reef species assemblages are associated with ambient soundscapes. Mar Ecol Prog Ser
Lammers MO, Brainard RE, Au WW, Mooney TA, Wong KB (2008) An ecological acoustic recorder (EAR) for long-term monitoring of biological and anthropogenic sounds on coral reefs and other marine habitats. J Acoust Soc Am 123:1720-1728
Mann DA, Locascio JV, Coleman FC, Koenig CC (2009) Goliath grouper Epinephelus itajara sound production and movement patterns on aggregation sites. Endangered Species Research 7:229-236