(Color online) An example of the system's resonance frequency and the slope used to calculate sound speed. This example is from a control replication of the Macrocystis trials.
Pictures of (a) Macrocystis pyrifera, (b) Egregia menziessi, and (c) Laminaria solidungula frond segments. The black arrows denote locations of pneumatocyst structures.
Empirical relationship between air volume within the pneumatocysts and kelp wet mass for individual Macrocystis pyrifera (r 2 = 0.90; p < 0.05) and Egregia menziessi (regression not significant) frond sections. Measurement uncertainty is ± 0.15 ml and ± 0.005 g for air volume and wet mass, respectively.
Decrease in effective sound speed in relation to free gas volume within pneumatocysts for Macrocystis pyrifera (r 2 = 0.70; p < 0.05) and Egregia menziessi frond sections (r 2 = 0.82; p < 0.01). The slope of the regression was significantly greater for Macrocystis compared to Egregia (z = 2.40; p < 0.05). Measurement uncertainty is ±0.15 ml and ±4 m s−1 for air volume and effective sound speed, respectively.
Decrease in effective sound speed in relation to total biomass for Macrocystis pyrifera (r 2 = 0.75; p < 0.05), Egregia menziessi, and Laminaria solidungula (regressions not significant). Measurement uncertainty is ±0.005 g and ±4 m s−1 for air wet mass and effective sound speed, respectively.
Effective sound speed of air-filled pneumatocysts compared to water-filled pneumatocysts of the same frond segments for (a) Macrocystis pyrifera and (b) Egregia menziessi. Measurement uncertainty is ±4 m s−1 for effective sound speed.
Change in effective sound speed upon air removal within pneumatocysts for Macrocystis pyrifera and Egregia menziessi frond segments. Trials for both species were plotted together (regression was not significant). Measurement uncertainty is ±0.15 ml and ±4 m s−1 for air volume and effective sound speed, respectively.
Effective sound speeds predicted by Wood's two-phase medium model for air and water components compared to observed effective sound speeds for frond segments of (a) Macrocystis pyrifera and (b) Egregia menziessi. A student's paired t-test revealed a significant difference between predicted and observed effective sound speeds for both Macrocystis and Egregia experiments (p < 0.01).
Model parameters obtained from morphological measurements and acoustic resonator experiments used to test multi-phase medium models. C composite and κ composite values are based on results from the derivation of Wood's two-phase medium model (Ref. 15 ). Values represent mean ± standard deviation for Macrocystis (n = 6), Egregia (n = 6), and Laminaria (n = 5).
Results of the experiments that examined the acoustic significance of air-filled and water-filled pneumatocysts. The superscripts correspond to the air-filled (a) and water-filled (w) pneumatocysts, respectively.
The measurements of kelp morphology for the specimens used in the modeling experiments. Each trial represents an independent replication of the resonator experiment.
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