Passive acoustics as a monitoring tool for evaluating oyster reef restoration

IntroductionApproximately 21 acres of oyster reef have been created in the Saint Lucie Estuary (SLE) in eastern Florida. With such a large scale restoration project, it is crucial to answer a vital question: was the restoration project successful? To answer this question, I propose a series of passive acoustical studies in the field and in the laboratory that will contribute to a better understanding of the oyster reef ecosystem and the success of oyster reef restoration projects. Reef bioacoustic signatures, sound intensity level, and sound type (e.g. snapping shrimp snaps) will be used to evaluate the success of the oyster reef restoration project. This proposed research aims to be the basis for future studies where biological sounds maybe used as a bioindicators for the overall health and biodiveristy of oyster reefs rather than direct sampling. The use of passive acoustics on invertebrate species has the potential to provide a new methodology to accurately monitor oyster reefs and other ecosystems, such as coral reefs and rocky reefs.

Hilde Zenil, Florida Oceanographic Society and Florida Atlantic University

Research ObjectivesObjective 1

Conduct field experiments to characterize temporal (seasonal) and spatial (in a salinity gradient) variations in signature sound production in living oyster reefs (natural and restored) of the eastern oyster, Crassostrea virginica, at three different locations along the St. Lucie Estuary (upstream, downstream, and mid-estuary).

Objective 2

Conduct field experiments and laboratory experiments to correlate seasonal variations in sound production and faunal assemblages between natural and restored oyster reefs in the St. Lucie Estuary.

Objective 3

Conduct field experiments to correlate the diel and seasonal variation in sound production and faunal assemblages in natural and restored oyster reefs at one region in the Saint Lucie Estuary.

Materials and methods – Study Site

All research will be conducted in the St. Lucie Estuary (SLE). The SLE receives in-flows of freshwater from the surrounding watershed and from Lake Okeechobee when lake levels must be lowered. The SLE is divided into three major regions: upstream, mid-estuary, and downstream. A restored and an adjacent natural reef were chosen for each of the three regions of the SLE (see Fig. 2). We selected the closest known natural reef to each restored reef.

Materials and methods – Sound Analysis

A hydrophone and a digital recorder will be used for acoustic sampling. The hydrophone will be attached to a buoy at a fixed distance from the buoy’s anchor. Deploying sites will be marked and recorded with a GPS from the start of the experiment, so the same locations are recorded each time. Each site will be recorder for 5 minutes.

Sound samples will be analyzed with SpectraPro and Matlab to analyze acoustic signatures and count the number of snapping shrimp snap spikes above a predetermined pressure threshold. The threshold was found by Radford et al. (2010). They found that snapping shrimp snaps have a specific pressure threshold at 4e6 Hz.

Materials and methods – Lift nets

Lift nets (50X50 centimeters) lift nets with 4 liters volume displacement of oyster shell will be deployed in two different habitats (natural and restored reef) at the mid-estuary site. Shell for the lift nets will be excavated from the reef where the lift net will be placed. Therefore, the shell in the lift net will have the same material and age as the oyster reef I want to study. The lift nets will be left for a month to allow recolonization of oyster inhabitants.

Materials and methods – Statistical Analysis

In all the three objectives multiway factorial analysis of variance (ANOVA) will be used to compare the factors that are measured. When factors in ANOVA are significantly different (p<0.05), Tukey’s test will be used to identify differences between means.

Preliminary ResultsPreliminary acoustic signal shows that there is a difference in acoustic signal between the natural and restored reefs. It is expected that as time progresses, the acoustic signature of fully restored reef will resemble the acoustic signature of the natural reef within the same region, representing a convergence of restored and natural habitats.

Literature citedRadford, C., Jeffs, A., Tindle, C., & Montgomery, J. (2008). Temporal

patterns in ambient noise of biological origin from a shallow water temperate reef. Oecologia , 156, 921-929.

Radford, C., Stanley, J., Tindle, C., Montgomery, J., & Jeffs, A. (2010). Localised coastal habitats have distinct underwater sound signatures. 401, 21-29.

AcknowledgmentsThe project was funded by National Atmospheric Administration (NOAA) as part of the American Recovery and Reinvestment Act of 2009.

I want to thank Vincent Encomio for all his support and guidance. I want to thank my committee members: Ed Proffitt, John Scanpa, and Grant Gilmore . Also I want to thank Elizabeth Salewiki and everyone that made this project possible.

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Fig 2 St. Lucie Estuary research sites.

Fig 1 Oyster reef restoration at the St. Lucie Estuary

Fig 3 Hydrophone and digital recorder.

Fig 4 Lift nest used to sample resident and transient fauna in oyster reefs.

Fig 5 Hilde Zenil (left) and Vincent Encomio during acoustic sampling.

Fig 6 Acoustic signatures for natural and restored oyster reefs.