Most bottom-dwelling marine organisms (e.g. crabs, mussels, corals) develop, zygotes and larvae, in the water column before settling on the sea floor. Reaching an appropriate habitat is critical in determining the distribution and abundance of adults, which make-up marine communities. It has recently been shown that underwater sounds may be an important cue used for marine fish and invertebrate larval in this process, yet the relevant acoustic patterns and associated larval responses remain largely unstudied. Therefore the goal of the research is to understand the nature of underwater sound in larval ecology. This will be done by characterizing an estuarine soundscape and determining how sound variation affects the settlement of invertebrates. The researcher will use larval oysters and clams, and the soundscape of estuarine habitats as a model system, results to date have established that oyster reefs are acoustically distinct from adjacent soft bottom habitats, and that these reef sounds enhance oyster settlement in laboratory experiments. This Doctoral Dissertation Improvement Grant project specifically seeks to expand upon these recent laboratory results by conducting field experiments to test if the apparent larval responses to habitat-related sound operate in the natural environment to shape settlement patterns. Building knowledge of the behavioral responses of marine larvae to bio-physical variables such as sound, and the resulting distribution and abundance patterns of marine organisms is central to improved understanding of marine biology. This work also highlights a potential biological implication of marine noise pollution and may elucidate previously untested benefits of soundscape diversity, ultimately leading to healthier and better-managed ocean and estuary ecosystems.

Project Report

A new study has provided the first evidence that underwater sound influences the settlement of reef-building larvae to oyster reefs, and that the addition of habitat-related sounds to the natural environment can increase the density of newly settled oysters. Reef-building organisms, such as oysters, are an ecologically and economically valuable resource worldwide, however, native populations are now less than 5% of their historical abundances due to fishing pressure, oyster bed destruction, habitat degradation and disease. Establishing the influence of ambient sounds on the early stages of reef-building organisms has broad implications for habitat restoration, and informs our understanding of the potential adverse effects of noise pollution in marine ecosystems. It also highlights the important role that ambient sounds play in marine biology. Marine seafloor ecosystems, and efforts to restore them, depend critically on the influx of larvae, since the early life stages of most bottom-dwelling organisms disperse in the water column for days to months prior to settlement. Understanding the drivers of the settlement process is central to successful prediction of reef population and community dynamics. Habitat-related soundscapes (the combination of biological and physical sounds from a particular location) may represent a valuable cue for a variety of larvae because these underwater sounds can indicate both the presence and biophysical characteristics of particular habitat types, and sounds can travel independent of currents over greater distances compared to other habitat cues (e.g. chemical odor). However, this phenomenon had not been tested in estuarine ecosystems, where tremendous habitat diversity supports a large array of commercially and ecologically important species that produce free-swimming larvae. With the support of a NSF Doctoral Dissertation Improvement Grant, Ashlee Lillis was able to conduct a series of field experiments to investigate the effect of habitat-related acoustic cues on larval settlement patterns of eastern oyster, an ecologically important reef-building species. Her study found cultured larvae attach in higher numbers when exposed to the distinct sounds of oyster reefs compared to the sounds of off-reef areas, and further experiments revealed that replayed oyster reef sounds can increase oyster settlement on natural substrates in the field. These findings establish a previously unrecognized influence of underwater soundscapes on a critically important ecosystem engineer, with broad implications for marine conservation and aquaculture programs.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
Standard Grant (Standard)
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emilia martins
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North Carolina State University Raleigh
United States
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