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Mytilus edulis growth rates from a three-month mesocosm experiment, Sylt, 2022

This dataset contains individual-level measurements of the blue mussel Mytilus edulis collected during a controlled mesocosm experiment at Sylt, Germany. Data were collected over a three-month period from 2 April 2022 to 27 June 2022. The experiment comprised twelve mesocosms, with four maintained at ambient temperature, four maintained at +1.5°C above ambient, and four at +3 °C above ambient. Observations include shell length, shell-length growth rates, and multiple biomass fractions, including total wet weight, wet tissue mass weight, shell-free dry weight, and ash-free dry weight, from which weight-based growth rates were calculated. All measurements were obtained using standard, traceable laboratory and field instruments. The dataset documents individual-level growth responses of M. edulis under controlled warming conditions and provides a reproducible resource for studies on physiological responses of coastal bivalves to temperature changes.

Mesocosm experiment on the influence of heatwave on plankton

In the context of global change, marine organisms are subjected not only to gradual changes in abiotic parameters, but also to an increasing number of extreme events, such as heatwaves. However, we still know little about the influence of heatwaves on the structure of marine communities, and experimental studies are needed to test the impact of heatwaves alone, and in combination with other environmental drivers. Here, we conducted a mesocosm experiment and applied an integrated multiple driver design to assess the potential impact of heatwaves under ambient and future environmental conditions on natural coastal plankton communities. To represent future environmental conditions, temperature and pH were manipulated based on the Representative Concentration Pathway 8.5 proposed by the IPCC for 2100, and dissolved N:P ratios were increased to simulate the conditions expected in European coastal zones. Throughout the experiment, we measured abiotic conditions as well as the abundance of bacterioplankton, phytoplankton, and microzooplankton.

Carbonate chemistry speciation of the 2023 KOSMOS Helgoland experiment on the effects of ocean alkalinity enhancement on pelagic foodwebs

This dataset contains carbonate chemistry speciation data of the 2023 KOSMOS mesocosm study on Helgoland, Germany. This study tested the effects of ocean alkalinity enhancement simulating lime additions on pelagic ecosystem functioning during a spring bloom. Carbonate chemistry speciation (fCO2, pHT, calcium carbonate saturation state) was generally calculated from measurements of total alkalinity (TA) and dissolved inorganic carbon (DIC) in depth-integrated water samples. There were 12 mesocosms in total and in 6 of them an alkalinity gradient of up to +1250 umol/kg was established in steps of 250 umol/kg. In the remaining 6 the same amount of alkalinity was added only to the upper portion of the mesocosms, resulting in twice the alkalinity increase there, before being mixed in after 48 hours. The two treatments simulated the immediate dilution of TA after ship deployment as well as a delayed one from a point source.

KOSMOS 2023 Helgoland mesocosm study on ocean alkalinity enhancement: sediment trap particle flux data and water column biogeochemistry

The data presented herein originates from a mesocosm study conducted as part of the BMBF CDRmare, Retake project (grant agreement no. 03F0895A), aimed at investigating the ecological ramifications of ocean alkalinity enhancement (OAE). Twelve mesocosms were deployed in Helgoland South Harbor, Germany, and systematically sampled using integrated water samplers over the period spanning from March 12th to April 20th, 2023. Six alkalinity levels under two dilution scenarios were established to differentiate between localized and uniform OAE additions. Alkalinity was increased stepwise to ΔTAmax = 1250 μmol kg-1 (250 μmol TA kg-1 increments) using sodium hydroxide (NaOH) with calcium chloride (CaCl2) to simulate cation release during calcium-based mineral dissolution, causing strong carbonate chemistry perturbations (e.g., pHT > 9.25). The dataset encompasses a spectrum of sediment trap particle flux data, water column biogeochemistry including pigment variables, inorganic nutrients, carbonate chemistry parameters. The study and data set offer insights into impacts of alkalinity enhancement on marine ecosystems and their associated biogeochemistry.

Reproductive success of stickleback lateral plate morphs

Reproductive success of threespine stickleback plate morphs (complete, low and partially plated) acclimated to ambient or +4°C sea water temperatures, and allowed to mate freely within large outdoor mesocosms set to either ambient or +4°C. The number of genotyped larvae assigned to each couple, total number of larvae in the clutch and reproductive success are given.

Mytilus edulis and Magallana gigas growth rates from a three-month mesocosm experiment, Sylt, 2023

This dataset contains individual-level growth rate measurements of the blue mussel Mytilus edulis and the Pacific oyster Magallana gigas, collected during a controlled mesocosm experiment in Sylt, Germany (coordinates are included in the dataset). Data were collected over a three-month period, from 29 March 2023 to 26 June 2023. Twelve mesocosms were used: six maintained at ambient temperature and six maintained at +3 °C above ambient. A randomized experimental design was used: six mesocosms contained only M. edulis, while the remaining six contained both species. Observations include shell length and daily shell-length growth rates, total wet weight (including shell) and daily growth rates based on weight. Each mussel was labeled and categorized by size class. Measurements were obtained using digital calipers (The Noble Finn, Model 150 mm) and laboratory balances (Type 00AC, Sartorius AG Göttingen, Germany), as well as handheld multiparameter instruments for water temperature. The dataset provides reproducible, traceable individual-level responses of M. edulis and M. gigas under controlled warming, supporting studies on physiological responses of coastal bivalves to temperature changes.

Microscale profiles of oxygen, pH and temperature through the sea surface microlayer in a mesocosm experiment during an algal bloom

The sea surface microlayer (SML) is the boundary layer on top of all oceans and is crucial for all exchange processes between the ocean and atmosphere. This less than 1 mm thick layer is heavily influenced by biological processes and events like algal blooms. To quantify the influence of an algal bloom in a controlled environment, we conducted a mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463°E). SURF is an 8.5 m long, 2 m wide and 1 m deep water basin, which can directly be filled with seawater from the Jade Bay, North Sea. The facility is equipped with a retractable roof, pumps for water circulation and dedicated mounts for multiple sensor systems. The mesocosm experiment was conducted from 18 May to 16 June 2023 as part of the project BASS (Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer). SURF was filled with seawater a few days before the start of the experiment (water depth 0.7 m). The water was then filtered and the surface skimmed to remove initial pollution. To prevent particle and microbial sedimentation during the experiment, the pumps operated at low speed to maintain gentle mixing of the water column. The roof of SURF was closed during the night, while it was open during the day except when it rained. To induce an algal bloom, a mix of nutrients (nitrogen, phosphorus and silicate) was added on 26 May, 30 May and 01 June. Based on the chlorophyll measurements which show the development of the bloom, three phases of the experiment were determined: the pre-bloom phase (18 May to 26 May), the bloom phase (27 May to 04 June) and the post-bloom phase (05 June to 16 June). Several physical, chemical and biological parameters were measured, which will be published in other datasets. To evaluate the impact of the algal bloom within the SML, oxygen concentration, pH, and temperature were measured in situ using microsensors (UNISENSE, Denmark) mounted on a MicroProfiling System (UNISENSE, Denmark). With this setup, direct in situ measurements inside both the thermal boundary layer and diffusion boundary layer at the sea surface can be made. One oxygen microsensor, two pH microsensors and three temperature microsensors were mounted on the microprofiler with their tips pointing upward to avoid disturbance in the SML. They were positioned a few centimeters apart. The microprofiler was used to automatically move the sensors down, from the air through the SML and into the underlying water over a total distance of 10 000 µm in steps of 125 µm (250 µm at the start of the experiment). At each depth, the sensors stayed for about 10 s, giving a mean value and a standard deviation over that time. Three of these measurements were taken at every depth before the sensor moved down to the next step. After completing a profile, the microprofiler returned to its initial position with the tips in the air to start the next profile. The resulting profiles mostly took between 40 to 50 minutes. These profiles were conducted continuously during day and night, except for small breaks to clean and if needed replace or readjust the sensors and recalibrate the pH sensors. The sensors' height required manual adjustment to position the tip precisely at the water surface (0 µm). Through this manual adjustment, small inaccuracies may occur. As a result, the sensor depth readings form the microprofiler system may not reflect the true sensor position, which can also vary between the sensors. The true sensor positions can later be obtained by analysing the measured profiles.

Physiological responses of Mytilus edulis and Magallana gigas from a three-month mesocosm experiment, Sylt, 2023

This dataset reports physiological measurements of two bivalve species, Mytilus edulis (blue mussel) and Magallana gigas (Pacific oyster), obtained during a three-month mesocosm experiment conducted in Sylt, Germany, in 2023. Physiological data were collected between 27 April 2023 and 25 June 2023.Twelve mesocosms were used to investigate the effects of temperature on individual-level physiological traits, with treatments including ambient temperature and ambient +3°C. Parameters measured include clearance rate, ingestion rate, and respiration rate. Environmental variables such as water temperature, depth, and sampling time were recorded for each measurement. Individual bivalves were labeled for tracking, and species identification followed WoRMS taxonomy. Measurements were performed using handheld multiparameter instruments and laboratory analyses. The dataset provides high-resolution, individual-based physiological responses of bivalves to moderate warming, supporting research on temperature-dependent feeding, metabolic processes, and energy flux in coastal ecosystems.

Biogeochemical variables from a Multidisciplinary BASS Mesocosm Study at Wilhelmshaven, 2023

This dataset contains biogeochemical variables measured during the same mesocosm experiment at Sea Surface Facility (SURF) in Wilhelmshaven, Germany (53.5148° N, 8.1461° E) in 2023. Variables include surfactants and nutrient concentrations, chlorophyll a, pigments, particulate and dissolved organic carbon and nitrogen, and several other biogeochemical parameters. These data complement the daily averaged physical parameters (PANGAEA DOI: https://doi.pangaea.de/10.1594/PANGAEA.983975) and together support the assessment of ecosystem and biogeochemical dynamics associated with the experiment, as described in the related publication Bibi et al., 2025.

Physical, chemical, and biogeochemical parameters from a mesocosm experiment at the Sea Surface Facility (SURF), Wilhelmshaven, Germany, spring 2023

This collection (bundled publication) includes datasets from a mesocosm experiment conducted in spring 2023 at the Sea Surface Facility (SURF), Wilhelmshaven, Germany (53.5148° N, 8.1461° E). The experiment initiated a phytoplankton bloom under controlled conditions to examine surface ocean biogeochemistry and sea-surface microlayer (SML) processes. Daily samples were collected from the SML and underlying water (40 cm depth) and analyzed for physical, chemical, and biological parameters. Measurements include meteorological conditions (air temperature, solar irradiance, and albedo), surfactants, nutrients, pigments, particulate and dissolved organic carbon and nitrogen, and additional biogeochemical variables. These datasets provide environmental and biogeochemical context supporting studies on surface ocean processes and are described in detail in the related publication Bibi et al. (2025).

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