Figure 1.
Oyster reserves at which sound recordings were made are marked (CH = Crab Hole; WB = West Bay). Field-based settlement experiment was conducted in West Bay.
Figure 2.
Larval settlement experiment (Laboratory) setup.
a) Side view schematic diagram of a replicate experimental tank (0.25 m×0.5 m) used in lab-based settlement experiment 1, showing the placement of a submerged speaker and container housing oyster larvae within a water bath, and b) Cylindrical treatment tank (20-L, 0.3 m water depth) used in lab experiment 2 containing an underwater speaker and five larval culture jars containing groups of actively swimming larvae. Larger view of larval culture jars with and without substrate is shown. No additional substrate was provided in experiment 1 and 2a; oyster shell discs were placed in the bottom of containers in experiment 2b.
Figure 3.
Larval settlement experiment (Field) setup.
a) Map of field experiment site in West Bay. Circles denote locations of “off-reef” replicates, and squares are “reef” replicates. The extent of the West Bay oyster reserve is indicated by the box bordering the reef replicates. Inset shows experiment location in West Bay, b) Schematic of the larval housing placed at each replicate in off-reef sites and c) in the reef site. Larval cultures were suspended at 1 m above the seabed at each location, with the two habitats providing the ambient sound treatments.
Figure 4.
Oyster reef and off-reef acoustic spectra for two Pamlico Sound sites.
Power spectral density for sounds recorded on and off-reefs taken monthly July-September at (a) West Bay and (b) Crab Hole. Because the field recordings differed in total length, each multi-hour recording was shortened to a one-hour sample that began at sunset.This produced six pairs of recordings collected simultaneously in each habitat type. The displayed data represent the median spectra for each hour-long sample calculated from a series of non-overlapping 10-sec duration windows.
Figure 5.
Spectral composition of sound in experiment 1 tanks (reef sound and no sound (control) treatments).
The black line represents the spectrum of the original in situ recording from West Bay oyster reserve that was replayed in reef sound tanks. Power spectral density estimated via Welch's method (Hamming window, 1-sec averages with 50% overlap).
Figure 6.
Spectral composition of one set of original and replayed sounds used in lab experiment 2.
a) Reef and off-reef sounds recorded simultaneously in West Bay, NC in July 2010. b) Comparison of in situ off-reef sound, replayed off-reef sound in experimental tank and no sound tank spectra. c) Comparison of in situ reef sound, replayed reef sound in experimental tank and no sound tank spectra. Power spectral density estimated via Welch's method (Hamming window, 1-sec averages with 50% overlap).
Figure 7.
Mean oyster settlement in reef sound and no sound treatments for laboratory experiment 1 trials.
Settlement was measured as proportion of larvae settled in a culture at the termination of a trial. Error bars represent 1 S.E. N = 28.
Figure 8.
Mean oyster settlement in reef sound, off-reef sound and no sound treatments for experiment 2 trials.
with a) no added substrate (N = 15), and b) with oyster shell substrate (N = 27). Letters denote statistically significant differences between treatments based on Tukey's HSD test. Error bars represent 1 S.E.
Figure 9.
Acoustic analysis of ambient underwater sound at field experiment sites.
a) Spectral composition of sound recorded at the reef and off-reef field sites during the field larval settlement experiments in August 2012. Power spectral density estimated via Welch's method (Hamming window, 1-sec averages with 50% overlap). b) Comparison of broadband root-mean square sound levels (in dB re 1 µPa) measured at the reef and off-reef site for the duration of the August 2012 field settlement experiment. The root-mean-square sound level was calculated in a series of non-overlapping 10-sec duration windows.
Figure 10.
Mean oyster settlement for field-based settlement experimental trials.
Settlement was measured as proportion of larvae settled in a culture at the termination of a trial. Error bars represent 1 S.E. N = 32.