The early life history of the clam Macoma balthica in a high CO₂ world

This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis were severely diminished: successful fertilization was reduced by 11% at a 0.6 pH unit decrease from present (pH 8.1) conditions, while hatching success was depressed by 34 and 87%, respectively at a 0.3 and 0.6 pH unit decrease. Under acidified conditions, larvae were still able to develop a shell during the post-embryonic phase, but higher larval mortality rates indicate that fewer larvae may metamorphose and settle in an acidified ocean. The cumulative impact of decreasing seawater pH on fertilization, embryogenesis and survival to the benthic stage is estimated to reduce the number of competent settlers by 38% for a 0.3 pH unit decrease, and by 89% for a 0.6 pH unit decrease from present conditions. Additionally, slower growth rates and a delayed metamorphosis at a smaller size were indicative for larvae developed under acidified conditions. This may further decline the recruit population size due to a longer subjection to perturbations, such as predation, during the pelagic phase. In general, early life history processes were most severely compromised at similar to pH 7.5, which corresponds to seawater undersaturated with respect to aragonite. Since recent models predict a comparable decrease in pH in coastal waters in the near future, this study indicates that future populations of Macoma balthica are likely to decline as a consequence of ongoing ocean acidification

LifeWatch observatory data : phytoplankton observations in the Belgian Part of the North Sea

Background This paper describes a phytoplankton data series generated through systematic observations in the Belgian Part of the North Sea (BPNS). Phytoplankton samples were collected during multidisciplinary sampling campaigns, visiting nine nearshore stations with monthly frequency and an additional eight offshore stations on a seasonal basis. New information The data series contain taxon-specific phytoplankton densities determined by analysis with the Flow Cytometer And Microscope (FlowCAM (R)) and associated image-based classification. The classification is performed by two separate semi-automated classification systems, followed by manual validation by taxonomic experts. To date, 637,819 biological particles have been collected and identified, yielding a large dataset of validated phytoplankton images. The collection and processing of the 2017-2018 dataset are described, along with its data curation, quality control and data storage. In addition, the classification of images using image classification algorithms, based on convolutional neural networks (CNN) from 2019 onwards, is also described. Data are published in a standardised format together with environmental parameters, accompanied by extensive metadata descriptions and finally labelled with digital identifiers for traceability. The data are published under a CC-BY 4.0 licence, allowing the use of the data under the condition of providing the reference to the source

In situ mortality experiments with juvenile sea bass (Dicentrarchus labrax) in relation to impulsive sound levels caused by pile driving of windmill foundations

Impact assessments of offshore wind farm installations and operations on the marine fauna are performed in many countries. Yet, only limited quantitative data on the physiological impact of impulsive sounds on (juvenile) fishes during pile driving of offshore wind farm foundations are available. Our current knowledge on fish injury and mortality due to pile driving is mainly based on laboratory experiments, in which high-intensity pile driving sounds are generated inside acoustic chambers. To validate these lab results, an in situ field experiment was carried out on board of a pile driving vessel. Juvenile European sea bass (Dicentrarchus labrax) of 68 and 115 days post hatching were exposed to pile-driving sounds as close as 45 m from the actual pile driving activity. Fish were exposed to strikes with a sound exposure level between 181 and 188 dB re 1 mu Pa-2.s. The number of strikes ranged from 1739 to 3067, resulting in a cumulative sound exposure level between 215 and 222 dB re 1 mu Pa-2.s. Control treatments consisted of fish not exposed to pile driving sounds. No differences in immediate mortality were found between exposed and control fish groups. Also no differences were noted in the delayed mortality up to 14 days after exposure between both groups. Our in situ experiments largely confirm the mortality results of the lab experiments found in other studies

A comprehensive study to assess the impact of impulsive sound on juvenile sea bass

Given the increasing amount of anthropogenically induced underwater sound into the marine environment, a better understanding of the impact of impulsive underwater sound on marine life is needed. This study tackles the impact of impulsive sound, related to pile-driving activities for offshore wind energy development, on the mortality, stress and behaviour of post-larval and juvenile European sea bass Dicentrarchus labrax. A 'worst-case scenario' field experiment was carried out on board of a piling vessel, exposing 68 and 115 days old fish (<2 g wet weight) to the sound generated during 1.5 hours of pile-driving. The number of strikes ranged from 1740 to 3070, with a single strike sound exposure level between 181 and 188 dB re 1 μPa².s, resulting in cumulative sound exposure levels ranging from 215 to 222 dB re 1 μPa².s. Immediate and long-term survival of the exposed fish was high and comparable to the control groups. However, juvenile fish responded to the impulsive underwater sound by a 50% reduction in their oxygen consumption rates, an indicator of secondary stress response. Primary stress responses, measured through cortisol levels are still to be analysed. We didn't find any effect on the condition and fitness of the exposed fish on the long term. Lab experiments performed with a SIG Sparker and a larvaebrator, respectively producing mid-high and lower frequencies, were inadequate to distinguish the determining sound metric or to pursue the exact origin of the stress response. Further away from the sound source, behavioural and masking effects can be expected. A lab experiment was carried out to study the behaviour of juvenile sea bass before, during and after one hour of impulsive sound exposure. In the aquaria, single strike sound levels reached 162 dB re 1 μPa².s, leading to a cumulative sound exposure level of 196 dB re 1 μPa².s after 2400 strikes. We observed that normal behaviour was disturbed, with an increase in startle responses and stationary behaviour at the beginning of the sound exposure experiment. Also, fish dived to the bottom of the aquaria, which is a typical anxiety-related response. However, no spatial preference was observed and normal behaviour was re-established shortly after the sound exposure ceased. These results indicate that impulsive sound close to the sound source creates sound pressure levels that are below the lethal threshold for fish, but above the stress threshold, at least for sea bass <2 g. Furthermore, lower sound levels at a distance from the sound source (in this case pile-driving) can disturb fish behaviour. Under optimal lab conditions, we did not see effects beyond the sound exposure period, but it remains unknown whether the reduced fitness of juvenile fish after exposure is limited in the real world as well

Acoustic data from drifts in the Belgian Part of the North Sea 2020-2021

Dataset collected to acquire underwater sound in the Belgian Part of the North Sea (BPNS) focusing on the spatial distribution. Data were obtained by hanging a hydrophone from a rope with weights while drifting.Between April 2020 and October 2020 and in June 2021, we recorded underwater sound at different strategic points of the Belgian Part of the North Sea (BPNS). All the recordings were acquired from a drifting small boat with a hydrophone attached to a rope with weights. The length of the rope was chosen according to the depth, so that the hydrophone would be in average more or less between the 1/2 and 1/3 of the top water column. The exact depth was not possible to know real-time because the plotter was turned off, so the rope length was kept constant during each entire deployment. In this manuscript, we consider a deployment the data corresponding to the time when a hydrophone is in the water without changing any recording parameter. Three different boats were used (RIB Zeekat, Sailing boat Capoeira and working boat from RV Simon Stevin). Each of these recording consists of 30 to 60 minutes of continuous recording following the current by drifting with the engines and the plotter turned off. Drifting was chosen as an ecologically meaningful approach to measure coastal benthic habitats (Lillis et al., 2018) and spatial resolution was chosen over temporal resolution considering the available ship time and equipment. The locations were chosen to cover the 5 habitat types defined in (Derous et al., 2007) as well as some shipwreck areas to capture their specific soundscapes. The objective was to acquire short recordings above different shipwrecks which would give information about acoustic spatial distribution. The recordings were acquired while drifting to diminish the possible flow noise due to the current. The instruments used where a SoundTrap ST300HF (sensitivity -172.8 dB re 1 V/uPa, from now on, SoundTrap) and a Bruel &amp; Kjaer Nexus 2690 and a hydrophone type 8104 (sensitivity -205 dB re 1 V/uPa, from now on, B&amp;K) together with a DR-680 TASCAM recorder. The amplification in the Nexus was set to 10 mV, 3.16 mV or 1 mV, depending on the loudness of the recording location. The SoundTrap was set to sample at 560 kS/s and the B&amp;K at 192 kS/s. To adjust for the different amplifications, at the beginning of each recording a calibration tone was performed. During each deployment, a GPS Garmin with a time resolution of 1s was synchronized with the instrument clock and stored the location during the entire deployment. A total of 54 different deployments were acquired. 14 of the sites were acquired simultaneously with the two recorders to confirm their interchangeability and assess their differences, so a total of 40 independent tracks were recorded. The metadata were stored in the Underwater Acoustics part of the European Tracking Network (ETN, https://www.lifewatch.be/etn/). Because acoustic changes in the soundscape were expected to be found in a small spatial (several meters) and temporal (several seconds) resolution, the data was processed in time windows of 2.5 seconds, overlapping 60%. The time window was chosen so the spatial resolution would be of 2 samples every 5 m, considering an average drifting speed of 1 m/s. All the acoustic processing was done using pypam (https://lifewatch-pypam.readthedocs.io/en/latest/). Each recorded file was converted to sound pressure using the calibration given by the manufacturer. For files with a calibration tone, the calibration value was computed from the tone and then the calibration signal was removed from the file. The rest of the data was processed according to the obtained calibration value. The sound pressure values obtained by the two instruments recording simultaneously where compared to make sure the calibrations where accurate. Per time window, first the Direct Current (DC) noise was subtracted by computing and subtracting the mean of the signal. Then a Butterworth band pass filter of order 4 was applied between 10 and 20,000 Hz, and the signal was down-sampled to twice the high limit of the filtered band. Once the signal of each time window was filtered to the desired bandwidth, the root mean squared value of the sound pressure of each one-third octave band (base 2) was computed per each 1 second-bin. This was done using a Butterworth band pass filter of order 2 per each one-third octave band, which resulted in 5 x 29 one-third octave bands per time window. Each acoustic sample was considered then to be these 5 consecutive one-third octave bands, with a total dimension of 5 x 29. A part from the acoustic features, each sample also stored a timestamp and the deployment metadata (instrument, end-to-end calibration, file path, hydrophone depth). The data are stored in one netCDF file per deployment, directly stored from pypam. Each netCDF file incorporated the deployment metadata together with the processed one-third octave bands. These files are stored in the deployments folder. The location of each expedition was stored in a gpx, which can be found under the gps/ folder. There is a data_summary_mda.csv file which summarizes the metadata for each deployment and links the deployment to the corresponding gpx file. Furthermore, some of the data were manually annotated for sound artifacts. These annotations are stored in the labels.csv file

North Sea soundscapes from a fish perspective : Directional patterns in particle motion and masking potential from anthropogenic noise

The aquatic world of animals is an acoustic world as sound is the most prominent sensory capacity to extract information about the environment for many aquatic species. Fish can hear particle motion, and a swim bladder potentially adds the additional capacity to sense sound pressure. Combining these capacities allows them to sense direction, distance, spectral content, and detailed temporal patterns. Both sound pressure and particle motion were recorded in a shallow part of the North Sea before and during exposure to a full-scale airgun array from an experimental seismic survey. Distinct amplitude fluctuations and directional patterns in the ambient noise were found to be fluctuating in phase with the tidal cycles and coming from distinct directions. It was speculated that the patterns may be determined by distant sources associated with large rivers and nearby beaches. Sounds of the experimental seismic survey were above the ambient conditions for particle acceleration up to 10 km from the source, at least as detectable for the measurement device, and up to 31 km for the sound pressure. These results and discussion provide a fresh perspective on the auditory world of fishes and a shift in the understanding about potential ranges over which they may have access to biologically relevant cues and be masked by anthropogenic noise