courseshub.world · Ecoacoustics · Module 08

Marine & Freshwater Ecoacoustics

Underwater soundscapes — from snapping shrimp at kHz to whale calls at sub-bass — and the shipping noise threatening their integrity.

whale call (20–200 Hz, 1000s km range)shipping noise (50–500 Hz)Ocean: water carries sound 4× faster than air over thousands of km

Underwater acoustics is an entirely different regime: water carries sound four times faster than air, with minimal attenuation, allowing low-frequency calls to propagate across ocean basins. Snapping shrimp dominate the high-frequency end of reef soundscapes; baleen whales operate at 20–200 Hz with active spaces of thousands of kilometres. Shipping noise — concentrated in the same low band as whale communication — has doubled the ocean's background noise level since 1960 in shipping lanes.

Module 08

Marine & Freshwater Ecoacoustics

Water's speed of sound (~1,500 m/s) is roughly 4.3× that in air, with different impedance matching and propagation characteristics.

SURFACE 0–200 m EPIPELAGIC snapping shrimp · fish choruses · dolphin echolocation 200–1000 m MESOPELAGIC whale song · deep-scattering layer migration 1000+ m BATHYPELAGIC / ABYSSAL infrasound · geological activity · shipping noise SOFAR CHANNEL
Figure 4. Acoustic stratification of the ocean. The SOFAR channel at ~1,000 m depth is a natural waveguide where blue whale calls propagate across ocean basins.

Coral Reef Acoustics

Coral reefs produce a distinctive acoustic fingerprint dominated by snapping shrimp (1–200 kHz broadband) and fish choruses (500 Hz – 2 kHz). Reef larvae use this soundscape to locate settlement sites.

Acoustic Rewilding
Steve Simpson (Exeter) demonstrated that broadcasting recordings of healthy reef soundscapes on degraded patch reefs increased fish larval settlement by up to 7×. This 'acoustic enrichment' is now being trialled as a reef restoration tool.

Why this matters

The SOFAR (Sound Fixing And Ranging) channel at ~1 km depth acts as a global acoustic waveguide: a single fin whale call can be detected on the other side of an ocean. Disrupting that channel through anthropogenic noise is functionally analogous to jamming the marine internet. Slowing ships by 10–15% reduces noise by 6–10 dB, with measurable behavioural recovery in nearby cetaceans within weeks.

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