Author: Jeroen Hubert

In a new paper, we introduce a design for a cost-effective, do-it-yourself valve gape monitor, aimed at measuring the extent of shell openings in bivalves like mussels and clams. This monitor can be used in the field, and offers a tool for monitoring of bivalve behaviour and health.

Bivalves play a vital role in aquatic ecosystems by filtering water and improving its quality. Their shell movements can provide important insights into how they are responding to environmental factors such as water quality, the presence of predators, or human disturbances. The valve gape monitor captures these subtle movements, offering a way to track bivalve health and monitor ecosystem changes.

The monitor makes use of a magnometer attached to one valve to measure the magnetic field strength, paired with a small magnet attached to the other valve. As the valve opens or closes, the distance between the magnet and magnometer changes, impacting the measured magnetic strength. This allows us to track the extent of shell opening. The monitor is built using affordable Arduino hardware and open-source software, and both the design and the code are make publicly available for other to replicate and use in own experiments.

We successfully tested the monitor in the field on three blue mussels, which were actively filter-feeding during most of the valve gape monitor deployment and also closing their shells occasionally. The latter behavior may indicate the disposal of feces and pseudofeces, or a response to a predator. These pilot results suggest that the monitor can reliably capture valve gape changes in response to the mussels’ behaviour, demonstrating the potential of this tool for broader ecological monitoring applications.

This affordable monitor opens up new possibilities for field researchers and environmental scientists to monitor bivalve activity, offering valuable insights into water quality and ecosystem health.

Read all about it in the paper: de Bruyn, W., Schendstok, J., & Hubert, J. (2024) VGWatch: A low-cost stand-alone monitor to measure the valve gape of bivalves in the field. Ecol. Indic. 163, 112085.

In a new paper, we have shown that Pacific oyster (Magallana gigas) larvae use sound to select suitable habitats.

Oysters begin their lives as pelagic larvae in search of a place to settle for the rest of their sessile lives. Selecting a suitable settlement location is thus of vital importance for their survival and fitness. They depend on external cues to find such a suitable location and sound was hypothesised to serve as one such cue. The preferred habitat of oysters is on hard substrate among conspecifics.

In a lab study, we exposed oyster larvae to playbacks of sound recordings from oyster reefs, vessels, a combination of oyster reefs and vessels, off reef (sandy bottom), and no sound at all. The larvae were most likely to settle during the playback of oyster reef sound. This confirms that oyster larvae use soundscapes to select suitable habitat. It may also be worthwhile to test whether speaker setups can be used for restoration purposes in the field.

Read all about it in the paper: Schmidlin, S., Parcerisas, C., Hubert, J.,  Watson, M.S., Mees, J., Botteldooren, D., Devos, P., Debusschere, E. & Hablützel, P.I. (2024). Comparison of the effects of reef and anthropogenic soundscapes on oyster larvae settlement. Sci. Rep. 14, 12580.

We just published a new paper ‘An experimental sound exposure study at sea: No spatial deterrence of free-ranging pelagic fish‘ and it’s open access (link)! The paper is authored by Jozefien M. Demuynck, M. Rafa Remmelzwaal, Carlota Muñiz, Elisabeth Debusschere, Benoit Berges, Hans Slabbekoorn and myself.

We performed a playback experiment at sea to explore the potential of sound in herding pelagic fish away from potential danger, for example pile driving or detonation of explosives. In order to test this, we made a transect of four frames (about 700 m apart) to monitor fish. During this period, we performed playbacks from a vessel and later derived fish presence and behaviour using the echosounders on the frames.

We found no responses to our sound playbacks, indicating that – at least the current sounds and levels – would not be successful in herding fish away from potential danger. We cannot exclude that other sounds would be successful, but it may also be that pelagic fish are more likely respond with subtle changes in schooling behaviour.

All data and scripts have been made publicly available too.

We published a new paper ‘Separate and combined effects of boat noise and a live crab predator on mussel valve gape behavior’ and it’s open access (link)! The paper is authored by Daniëlle van der Burg, Rob Witbaard, Hans Slabbekoorn and myself.

Mussels can respond to various stimuli by closing their valves. This protects their soft tissue, but limits their feeding behaviour. In the current study, we wanted to know whether a combination of – potentially threatening – stimuli would elicit even stronger responses. The test this, we exposed mussels to sound (boat or ambient playbacks) and a live crab predator (chemical cues only, a ‘free-ranging’ crab, or a control without crab).

Mussels had a lower valve gape during boat sound and when the ‘free-ranging’ crab was present. The combination did not lead to an even lower valve gape. We also showed that the proximity of the ‘free-ranging’ crab to the mussel was linked to the valve gape of the mussel.

Nature is complex and full of stimuli. That’s why it’s important to not only study the effect of single stressors, but also to combine them and prevent ‘ecological surprises’.

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All data and scripts have been made publicly available too.

We just published a new paper ‘Acoustic disturbance in blue mussels: sound-induced valve closure varies with pulse train speed but does not affect phytoplankton clearance rate‘ and it’s open access (link)! The paper is authored by Rosalie Moens, Rob Witbaard, Hans Slabbekoorn and myself.

Mussels have been shown to respond to sound by closing their valves. We wondered whether different types of sound would affect mussels differently, and whether sound-induced valve gape closure meant that cleared (or consumed) less phytoplankton from the water.

We found that mussels that were exposed to pulse trains with a longer pulse interval took longer to return to pre-exposure baseline levels. We also found a link between valve gape and phytoplankton clearance rate, but no effect of the sound treatment on their clearance rate. We showed that different sound exposures can impact mussels differently, which is relevant for impact assessments and mitigation measures. Future research should also test the effects of sound on mussels in the field.

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We just published a new paper ‘Responsiveness and habituation to repeated sound exposures and pulse trains in blue mussels‘ and it’s open access (link)! The paper is authored by Emily Booms, Rob Witbaard, Hans Slabbekoorn and myself.

Mussels live in an almost fixed location and are therefore likely to be exposed to the same sound repeatedly. They have been shown to close their valves upon sound exposure, which may disturb their filter feeding behaviour. It may be that the their response changes over repeated sound exposures.

To study this, we equipped mussels with a valve gape monitor and repeatedly exposed them to sound (or a silent control). Initially, the mussels responded to the sound very clearly, but this decayed over repeated exposures. Then, we exposed the mussels to a novel sound to test whether the decay in responsiveness could be explained by habituation. See the paper for those results.

This experiment took place during the first COVID-19 lockdown, and was therefore performed at the house of one of the authors. The mussels were kept in a nearby restaurant with a salt water aquarium.

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We published a new paper on the effects of a seismic survey on the behaviour of Atlantic cod. We tagged and tracked Atlantic cod in an offshore windfarm and had a seismic survey passing by in parallel tracks for a 3.5-day period. Seismic surveys are performed to map the seafloor and use loud impulsive sound to do so. During the survey, cod changed their activity patterns, during and after the survey, more cod than expected left the area. Studies like this help to yield insight into the effects of human activities on fish populations. The paper was published in Current Biology by Inge van der Knaap, Jan Reubens, Len Thomas, Michael A. Ainslie, Hendrik V. Winter, Jeroen Hubert, Bruce Martin, and Hans Slabbekoorn.

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