Inter-seasonal comparison of acoustic propagation in a Thalassia testudinum seagrass meadow in a shallow sub-tropical lagoon

Abstract

Acoustic propagation measurements were collected in a seagrass meadow in a shallow lagoon for periods of over 65 h in winter and 93 h in summer. A bottom-deployed sound source transmitted chirps (0.1–100 kHz) every 10 min that were received on a four-receiver horizontal hydrophone array. Oceanographic probes measured various environmental parameters. Daytime broadband acoustic attenuation was 2.4 dB greater in summer than winter, and the median received acoustic energy levels were 8.4 dB lower in summer compared to winter. These differences were attributed in part to seasonal changes in photosynthesis bubble production and above-ground seagrass biomass.

Intertidal Soundscapes of Hardened and Living Shorelines: A Case Study of Habitat Enhancement

“…The sounds that contributed to this mean SPL difference seemed largely biological in origin, likely predominantly snapping shrimp snaps (Breder, 1968;Mathews, 2006). Measured transmission loss, however, was similar between the two sites (Figure 6) and, if anything, attenuation would likely be higher at the living shoreline site because of the presence of salt marsh grasses (Arenovski & Howes, 1992;Biggs & Erisman, 2021;Felisberto et al, 2015;Hopson, 2019;Lee et al, 2023;Miksis-Olds & Miller, 2006). The detected increase in mean SPL was, therefore, more likely the result of increased sound-producer abundance and/or sound-production rates (Lillis & Mooney, 2022;Wall et al, 2021).…”

“…Within the salt marsh planting, however, transmission loss would likely be high (Supporting Information Figure S5). Aquatic plant species, such as S. alterniflora that was planted at the living shoreline site, can develop complex gas transport and lacunal allocation systems as well as produce bubbles through photosynthesis, with potentially substantial impacts on sound travel (Arenovski & Howes, 1992; Felisberto et al, 2015; Hopson, 2019; Lee et al, 2023; Maricle & Lee, 2002; Miksis‐Olds & Miller, 2006). In fact, a similar study in freshwater wetland habitats found significant impacts of both distance and vegetation presence on attenuation (Hopson, 2019).…”

“…In fact, a similar study in freshwater wetland habitats found significant impacts of both distance and vegetation presence on attenuation (Hopson, 2019). Attenuation through plants may also exhibit seasonal variation related to changes in above‐ground biomass and bubble production (Lee et al, 2023). In addition to plants, the introduction of both artificial structures and sand at the living shoreline could have also had meaningful effects on attenuation through changes to sound speed through solid structures, the possible introduction of gas pockets, the scattering properties of different sediments and variation in effects based on frequency (Li et al, 2019; Nyborg & Rudnick, 1948; Rogers & Cox, 1988; Wang et al, 2021; Yang & Tang, 2017).…”

“…In contrast with some of the more acoustically well‐studied ecosystem types that are dominated by harder habitat structures (e.g., oyster shells, coral skeletons) and that occur subtidally, living shorelines are often dominated by plant material and occur in shallow or intertidal zones, which can impact how sound travels and attenuates (Biggs & Erisman, 2021; Haupert et al, 2023; Lee et al, 2023; Miksis‐Olds & Miller, 2006). Air associated with plants from photosynthetic bubble production, internal lacunae and gas transport systems can dampen sounds travelling through them, with accordingly greater effects with increased density (Arenovski & Howes, 1992; Hopson, 2019; Lee et al, 2023; Maricle & Lee, 2002; Miksis‐Olds & Miller, 2006). Other environmental factors, such as temperature, salinity and water depth, can also have impacts on transmission loss, limiting the distance ecologically relevant signals can travel (Biggs & Erisman, 2021; Haupert et al, 2023; Miksis‐Olds & Miller, 2006).…”

Pulsed sounds caused by internal oxygen transport during photosynthesis in the seagrassHalophila ovalis

“…Seagrasses have aerenchyma tissues with continuous air-filled lacunae in leaves, rhizomes, and roots (Armstrong, 1979; Larkum et al, 1989; Borum et al, 2006; Mckenzie, 2008). The lacunae allow movement of photosynthetic oxygen produced below the leaf epidermis to flow to petioles, stem, rhizomes, and roots (Roberts et al, 1984; Lee et al, 2023) by phase diffusion (Sorrell and Dromgoole, 1987). The lacunae in leaf and rhizome are connected and have diaphragms at the nodes and transitional regions (Larkum et al,1982).…”