Assessing the low frequency acoustic characteristics of Macrocystis pyrifera, Egregia menziessi, and Laminaria solidungula

Abstract

The acoustic properties of kelp forests are not well known, but are of interest for the development of environmental remote sensing applications. This study examined the low-frequency (0.2-4.5 kHz) acoustic properties of three species of kelp (Macrocystis pyrifera, Egregia menziessi, and Laminaria solidungula) using a one-dimensional acoustic resonator. Acoustic observations and measurements of kelp morphology were then used to test the validity of Wood's multi-phase medium model in describing the acoustic behavior of the kelp. For Macrocystis and Egregia, the two species of kelp possessing pneumatocysts, the change in sound speed was highly dependent on the volume of free air contained in the kelp. The volume of air alone, however, was unable to predict the effective sound speed of the multi-phase medium using a simple two-phase (air + water) form of Wood's model. A separate implementation of this model (frond + water) successfully yielded the acoustic compressibility of the frond structure for each species (Macrocystis = 1.39 ± 0.82 × 10(-8) Pa(-1); Egregia = 2.59 ± 5.75 × 10(-9) Pa(-1); Laminaria = 8.65 ± 8.22 × 10(-9) Pa(-1)). This investigation demonstrates that the acoustic characteristics of kelp are species-specific, biomass-dependent, and differ between species with and without pneumatocyst structures.

Automated Filtering of Multibeam Water-Column Data to Detect Relative Abundance of Giant Kelp (Macrocystis pyrifera)

“…Single-beam and split-beam echosounders operating at 120 kHz or 200 kHz have been used to detect the presence of kelp [19], measure its canopy height [20], or map its distribution [21][22][23][24]. The availability of strict but practical calibration protocols [25], standard data processing methods [26], and laboratory measurements of acoustic properties of kelp [27][28][29][30] may even allow using these systems to estimate kelp biomass. However, these systems have a limited angular aperture (usually of the order of 1-10 • ), which results in a very limited spatial coverage.…”

A Monte Carlo experiment for measuring acoustic properties of macroalgae living tissue

“…Large pieces were placed in a resonator tube to investigate their "low-frequency" behavior in accounting for both tissue structure and elastic properties. 3 Ultrasonic techniques 4 were adapted to directly measure intrinsic properties of distinct tissue types. 5 For both measurement types, suspensions were prepared with well blended tissue and artificial seawater (ASW) to form a "soup"-like heterogeneous mixture from macroalgae 5 or seagrass; 6 however, acoustic properties could potentially be transformed through breakdown of cell structure.…”