Author Dominic McAfee talks us through his and colleagues’ recently published research article which experimented with the use of home-made speakers to boost oyster recruitment at sites throughout Australia.
We’ve all, at one time or another, used music as a band aid. Perhaps to mend a broken heart, or to help us through challenging times. And in this regard, it seems we are not alone – even relatively simple animals use attractive sounds to make important life decisions. But could the sounds of the sea be used to boost the repair of marine ecosystems? We decided to investigate the sensory world of some of the more simple marine animals to answer this question.
Active, not passive drifters
Recent research suggests that even very simple, microscopic organisms are much more than passive drifters. For a long time, it was assumed that marine larvae just drifted on the tide, with larval recruitment determined by the luck of ocean currents. But – they are actually sensory creatures. Many marine larvae interpret sight, smell, and sound to navigate, and can follow these cues to actively seek a suitable home to settle down.
We are now utilising this incredible sensory ability to illicit immense benefits for our shellfish restoration efforts. We use underwater speakers to play the most seductive sounds of the sea to attract brainless larval oysters towards our reef restorations. Before delving deeper, let’s talk about how we got here.
Bringing back a lost ecosystem
Over the past 200 years, an astonishing amount of shellfish reef has been lost worldwide. Formed by oysters and mussels, shellfish reefs were extracted from hundreds of thousands of kilometres of temperate coastline. For example, in Australia, flat oyster reefs covered thousands of coastal kilometres, but were eradicated from mainland Australia by a colonial oyster dredge fishery. Today, shellfish reefs are likely the most decimated marine ecosystem worldwide.
But, humanity’s destructive relationship with shellfish reefs may be at a turning point. Recent recognition of the social and ecological value of shellfish reefs is now seeing restoration efforts rapidly rise to repair the health and productivity of coastal seas. This typically involves placing hard substrate, such as boulder reefs, on the seafloor to provide a settlement site atop which shellfish reefs can grow. A major challenge facing these projects is to ensure sufficient oyster or mussel recruitment to seed the recovery process.
The problem is that most shellfish restorations occur along heavily degraded coastlines that have lost the environment cues that organisms use. These are often sedimentary areas with little biological sound. So, although the provided substrate may be suitable, marine larvae may not be able to find it. Cue our sound research!
What marine music do oysters like?
Our use of sound at restoration sites builds upon several years of investigating which marine sounds our native oysters are particularly attuned too. First, we recorded the sounds associated with the main marine habitats within our local gulf – South Australia’s Gulf St. Vincent – sedimentary habitats, seagrass meadows, and macroalgae rocky reefs (1,500 km of oyster reef has been completely lost from this coastline).
Next, we played these habitat sounds to oyster larvae in the lab, finding a strong preference for noisy reef soundscapes, which induced larvae to dive and attach to the bottom. Finally, we built an 8 m long tank (dubbed the oyster raceway) with a speaker at one end and found that oyster larvae actively swim towards attractive marine sounds. This new knowledge alludes to far more dynamic larval dispersal than previously thought.
Utilising soundscapes to boost marine restoration
But it was our field results that were really exciting. We placed our own home-made speakers across two of the largest reef restorations in Australia. At 8 of our 10 sites, our speakers significantly boosted oyster recruitment by as much as 18 times, equating to up to 17,000 more oysters per square metre. And that was just after one month! After 5 months, this boost in early recruitment resulted in more large oysters that coalesced to form more of the vertical habitat that provides a home for other animals.
Of course, we have much learn. What other species are drawn in by our speakers? Could this create recruitment sinks? But in boosting a key process for restoration success, our results suggest that playing the sounds of the sea may provide a surprising tool for enhancing restoration outcomes.
Read the full Open Access article, “Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations” in Journal of Applied Ecology
