Coastal Soundscapes and Oyster Reef Health

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The eastern oyster Crassostrea virginica is a key foundation species on the Virginia coast that forms the basis of complex reef communities. These oyster reefs are important for coastal ecosystem health, as they improve water quality by filtering the water column, as well as provide habitat to a wide variety of marine organisms, including fish, blue crabs, and mussels.

Unfortunately, extensive overharvesting, low water quality, and disease have combined to decimate Virginia oyster populations, resulting in current abundances approximately 1% that of 19 th century levels. As a result, the University of Virginia and The Nature Conservancy (TNC) have been conducting efforts to restore oyster reefs along Virginia’s Eastern Shore.

Oyster reefs on the Virginia coast inhabit the harsh intertidal zone, where organisms must be adapted to both submerged and exposed conditions. Oysters consume oxygen, and their rate of oxygen consumption can be used as a measure of their feeding rate and overall health. Oysters, shrimp, fish, and a host of different animals that inhabit these reefs also generate unique sounds, which when combined with the sounds of the water and the waves result in a rich soundscape that describes the activity of these systems.

Our research represents a novel combination of field-based oxygen flux measurements and bioacoustic sound recordings made over natural and restored reefs on the Virginia coast. As part of this work we have been able to identify the unique sounds of several animals, including snapping shrimp, croaker, oyster toadfish, as well as of the oysters themselves.

Oysters emit sound when they rapidly close their shells, either as a way to expel waste products or for protection, which allows us to track their behavior through the soundscape.

By linking these sound data to our biological oxygen-uptake measurements, we are able to better describe how reef activity changes over daily and tidal cycles. This work has important implications for better understanding oyster behavior and for measuring overall health of the oyster reef ecosystem.

Beyond just environmental research, we are also in the process of mapping reef noise to different sounds in order to create music. To do this an immersive sound model of one of the reefs is being created using hundreds of hours of stereo hydrophone recordings.

Using these recordings as data, four frequency sub-bands are analyzed and segmented to generate events with different intensity, directionality, and duration. These events are tagged by their location in the tide cycle and used to train a Markov model. After selecting or dynamically changing a “tide location” variable, the 4-dimensional output of this model may be mapped on to different sets of sounds (using AcousMIDI), effectively recreating the biotic and abiotic activity of the oyster reef in any number of different sound worlds.