New paper: Effects of sound on mussel-crab interaction

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’.

All data and scripts have been made publicly available too.

New paper: Mussels’ response to sound is affected by pulse rate

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.

New paper: Response and habituation of mussels to repeated sound exposures

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.

New paper: Effects of a seismic survey on cod

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.

New paper: No evidence for cross-modal interference in shore crabs – a T-maze study

We just published a new paper ‘No negative effects of boat sound playbacks on olfactory-mediated food finding behaviour of shore crabs in a T-maze‘ and it’s open access (HTML/PDF)! The paper is authored by Jostijn J. van Bemmelen, Hans Slabbekoorn and myself.

We are interested in the effects of man-made noise on marine life. Naturally, one would expect disturbance of behaviour that relies on biologically relevant sound. However, the processing of noise by an animal, may also interfere with the processing and interpretation of non-acoustic cues; for example, an olfactory cue (smell).

To study this, we allowed shore crabs to find food in a T-maze. We placed a food item in one of the ends of a T-maze. The crab could not see or hear the food, so had to find it based on smell. To facilitate this, we created a continuous waterflow from both ends to the starting area of the maze (as demonstrated in the color-test below). We tested two crabs at the same time and exposed about half of all of them to boat sound playbacks and the other half to ambient (background) sound playback. We scored how fast and efficient the crabs were in finding the food. Crabs that were exposed to boat sound were not slower or less efficient in finding the food, so we concluded that boat sound did not interfere with the processing and interpretation of smell in the current experiment.

Jostijn is constructing the experimental set-up.

In the YouTube-playlist above, you find several example trials (at normal speed) and some additional explanation on how we conducted the trials.

New paper: effect of sound exposure on time budgets of Atlantic cod

We just published a new paper ‘Effects of seismic airgun playbacks on swimming patterns and behavioural states of Atlantic cod in a net pen‘ and it’s open access (HTML/PDF)! The paper is part of the PCAD4Cod project and is authored by James A. Campbell, Hans Slabbekoorn and myself.

Increasing amounts of studies are being conducted on the effects of sound on marine life, including fish. However, it remains complex to translate results from controlled experiments to consequences for fitness of an individual or population. A first step might be to quantify time spent performing particular behaviour, and changes therein due to sound exposures. In the future, these changes in time budgets may be translated to changes in energy budgets, and consequently to changes in growth, reproduction, and mortality.

We used Atlantic cod as our study species and tracked them for about a day while swimming in our floating pen set-up (see pictures). After about 20 hours of baseline conditions, we exposed them to an hour of seismic survey sound playback. Firstly, we showed that the cod did not immediately changed their swimming patterns upon sound exposure onset. Next, we used statistical models to classify the behaviour of the fish and modelled the behaviour as if no exposure had taken place. Here, we saw that some fish seemed to have changed their time spent performing certain behaviour. This may be translated to changes in energy budgets and consequently individual and population fitness consequences in the future.

New conference paper: An experiment to test the effects of sound on the time budget of fish

We just published a new conference paper ‘Exploring effects of sound on the time budget of fishes: An experimental approach with captive cod‘ and it’s open access (PDF)! The paper is part of the PCAD4Cod project and is authored by Daniël A. Wille, Hans Slabbekoorn and myself.

There’s an increasing interest into the effects of anthropogenic sound on marine animals including fish. A variety of studies is being conducted to gain insight into these effects. Ultimately, we want to gain insight into the effects of sound on individuals’ fitness and population levels. Modeling studies show that changes in energy expenditure and intake have most potential to lead to population levels effect. So, it’s important to study the effect of sound on individuals’ time and/or energy budget.

Ideally, this is studied in the field, but it’s very challenging to track free-ranging fish in their natural environment at high resolution. For that reason, we conducted a pilot study in a basin. We videoed 3 pairs of Atlantic cod for 7 hours per day, for 6 consecutive days. We exposed them to the playback of seismic survey sound for 3 consecutive days and a silent control for another 3 consecutive days. Each morning, we introduced live crabs in the experimental basin and the cod exhibited natural foraging behaviour by scanning and lifting patches of oysters in search for the crabs.

From the daily 7 hours of video footage, we extracted 20 second clips every five minutes (see example clips below). We scored the most dominant behaviour of both fish (foraging, swimming or stationary). In this way, we got insight in the activity budgets of individual cod with and without sound exposure. This can be translated to energy budgets by determining the energy expenditure and intake in all behavioural states.

The experimental basin.

New paper: Effects of acoustic features of sound exposures on fish’s behavioural responses

We just published a new paper ‘The role of ambient sound levels, signal-to-noise ratio, and stimulus pulse rate on behavioural disturbance of seabass in a net pen‘ and it’s open access (HTML/PDF)! The paper is a collaboration between Leiden University and Wageningen Marine Research and is authored by Errol (Y. Y.) Neo, Erwin (H. V.) Winter, Hans Slabbekoorn and myself.

We are interested in the effects of man-made sound on marine life, including fish. Sound exposures can have a range of effects on fish; it may mask communication or other biological relevant sounds, elicit physiological and behavioural responses, and may even induce physical damage (close to a loud sound source). The sound levels are often used to predict the potential harm of sound exposure, however the acoustic characteristics of the environment (ambient noise) and sound exposure itself (the potentially disturbing stimulus) may also influence the behavioural responsiveness of animals.

Underwater, ambient noise mainly originates from water surface roughness from weather conditions and boat noise. When ambient noise levels are higher, a potentially disturbing stimulus may stand out less strongly (lower signal-to-noise ratio) and thereby elicit a milder behavioural response. Also, the potentially disturbing anthropogenic sounds themselves vary in acoustic characteristics which may affect fish differently, for example the rate at which poles (e.g. of wind turbines) are being driven in the seabed or the rate at which airguns of seismic surveys are being fired.

We tested the effect of such acoustic characteristics by exposing 16 groups of four European seabass to multiple impulsive sound treatments that varied in elevated background level, pulse rate, and pulse level. We implanted the fish with acoustic tags to be able to track the positions of the individual fish. We showed that the seabass increased their swimming depth after the start of the sound exposure, however the variation in the response could not be explained by any of the tested acoustic characteristics. Nevertheless, based on our review of the literature, we think it is worthwhile to continue on this line of research by testing wider ranges of signal and background levels.

Running a sound exposure trial. In the middle, you see the equipment we used to log the acoustic tag recordings and the amplifier of the underwater speaker (photo 2014).
We measured sound levels accross the net pen. On the background, you see the Oosterscheldekering (Eastern Scheldt storm surge barrier).

Citation: Hubert, J., Neo, Y. Y., Winter, H. V., & Slabbekoorn, H. (2020). The role of ambient sound levels, signal-to-noise ratio, and stimulus pulse rate on behavioural disturbance of seabass in a net pen. Behavioural Processes, 170, 103992. DOI. [Open Access: HTML/PDF]

P.s. During the field season in which we collected data for the current paper, the Dutch TV programme ‘Vroege Vogels’ visited our field site to make an item on the effects of sound on fish in general, and about another study we did on an acoustic deterrent device for fish. For this, we also used the floating pen and a highly simular experimental design, so it may be interesting to watch the tv item (from 14:35 min on):

European seabass (our study species).
Assembling the study island and loading it with 150 kg anchoring blocks (photo 2014).
Anchoring the platform at the right location. We used a combination of chains and stretchable bungee ropes to keep the island in place throughout tides (photo 2014).
In the artificial cove ‘Jacobahaven’, our fieldsite (photo 2014).