Season-Specific Effects of Marine Heatwaves on Macrofaunal Community Composition and Ecosystem Processes

Norman Göbeler, Alf Norkko, Joanna Norkko

The dataset provides macrofaunal community data, alongside sediment characteristics, and oxygen/nutrient flux rates, from a laboratory experiment in 2021 exposing intact sediment cores from Storfjärden to marine heatwaves across seasons.

Marine heatwave research has focused mainly on summer extremes, leaving it unclear whether benthic communities and ecosystem processes respond differently to heatwaves occurring in other seasons.

Intact sediment cores (9 cm diameter, GEMAX corer) were collected at Storfjärden near Tvärminne Zoological Station, Finland, during winter, spring, summer, and autumn 2021, and incubated under control versus heatwave temperatures in climate-controlled rooms for 15 days per season.

MarineSeasonal MHWClimate changeMarine heatwavesEcosystem processesEcosystem metabolismSeasonalityBenthic communityBenthic-Pelagic couplingCoastClimBenthic ecology

Name

Version

Citation

References

Göbeler, N., Norkko, A. & Norkko, J. Season-Specific Effects of Marine Heatwaves on Macrofaunal Community Composition and Ecosystem Processes. Ecosystems 29, 78 (2026). https://doi.org/10.1007/s10021-026-01098-4

Data description

This dataset is used in Göbeler et al. (2026), Season-specific effects of Marine Heatwaves on macrofaunal community composition and ecosystem processes.

Data are provided as eight csv files, described below. Each file corresponds to one stage of the analysis: experimental treatment temperatures, field monitoring temperatures, macrofaunal community composition, sediment organic matter and porewater nutrients, and oxygen/nutrient flux rates. R scripts used to process these files and reproduce all figures and tables are provided alongside the data (see Code availability).

Data files

• Daily_average_Temperature_MHW.csv Daily mean experimental temperature in the MHW treatment tanks across all four seasonal experiments in 2021, with the 1931-2020 reference-period climatology and thresholds used for marine heatwave detection.
• Daily_average_Temperature_controls.csv Daily mean experimental temperature in the control tanks, with the 1931-2020 reference-period climatology and thresholds used for marine heatwave detection.
• YSI_Storfjarden_MHW.csv Long-term field-monitoring temperature at Storfjärden (MONICOAST, 30 m depth) for 2021, with marine heatwave detection output.
• Community.csv Macrofaunal abundance and biomass per sediment core, by taxon and sediment depth layer.
• Community_sizes.csv Individual shell-length measurements of Macoma balthica, used to separate adult and juvenile size classes.
• PW_OM_nutrients_depth_profile.csv Sediment organic matter content and porewater nutrient concentrations by sediment depth.
• Seasonal_MHW_nutrients.csv Oxygen and nutrient concentrations measured at the start and end of core incubations, used to compute flux rates.
• Fluxrates.csv Oxygen and nutrient flux rates computed from Seasonal_MHW_nutrients.csv.

File content details

Daily_average_Temperature_MHW.csv

Number of variables: 13 Number of cases/rows: 365 Missing data codes: NA

• factored_depth Sensor depth label (bottom, for all rows).
• doy Day of year.
• date Date (yyyy-mm-dd).
• treatment Experimental treatment (MHW).
• season Season of the experiment (Winter, Spring, Summer, Autumn).
• phase Experimental phase (Acclimation, MHW_1, MHW_2, MHW_3).
• mean_temp (°C) [temperature] Daily mean tank temperature.
• sd (°C) Standard deviation of daily mean temperature.
• n Number of temperature loggers/readings averaged.
• se (°C) Standard error of daily mean temperature.
• rp31_20_mean (°C) [temperature] Climatological mean temperature for that day of year, reference period 1931-2020.
• rp31_20_q10 (°C) [temperature] 10th percentile temperature, reference period 1931-2020.
• rp31_20_q90 (°C) [temperature] 90th percentile temperature, reference period 1931-2020; used as the moderate marine heatwave threshold.

Daily_average_Temperature_controls.csv

Number of variables: 13 Number of cases/rows: 366 Missing data codes: NA

Same structure as Daily_average_Temperature_MHW.csv (date, treatment, factored_depth, doy, season, phase, mean_temp, sd, n, se, rp31_20_mean, rp31_20_q10, rp31_20_q90)

YSI_Storfjarden_MHW.csv

Number of variables: 12 Number of cases/rows: 365 Missing data codes: NA (used in threshold/event-related columns on days that were not part of a detected event)

• date Date (yyyy-mm-dd).
• doy Day of year.
• station Monitoring station name (Storfjärden).
• temperature (°C) [temperature] Daily mean field temperature at 30 m depth.
• climatological_mean (°C) [temperature] Climatological mean temperature for that day of year, reference period 1931-2020.
• threshold (°C) [temperature] Moderate marine heatwave threshold (90th percentile).
• threshold_2x (°C) [temperature] Strong marine heatwave threshold.
• threshold_3x (°C) [temperature] Severe marine heatwave threshold.
• thresh_criterion Logical; whether temperature exceeded the moderate threshold on that day.
• duration_criterion Logical; whether the minimum 5-day duration criterion for a marine heatwave (Hobday and others 2016) was met.
• event Logical; whether the day was part of a detected marine heatwave event.
• event_no Sequential ID of the detected marine heatwave event.

Community.csv

Number of variables: 17 Number of cases/rows: 240 Missing data codes: #N/A

• date Date (yyyy-mm-dd).
• season Season (Winter, Spring, Summer, Autumn).
• parameter Whether the row holds abundance or biomass data (Community_Abund, ind. m⁻²; Community_Mass, g m⁻²).
• phase Experimental phase (Acclimation, MHW_1, MHW_2, MHW_3).
• treatment Control or MHW.
• replicate Replicate core number.
• sediment_depth (cm) Sediment depth layer: 0 (0-3 cm), 3 (3-10 cm), or 10 (>10 cm).
• macoma Macoma balthica.
• hydrobidae Hydrobiidae.
• ostracoda Ostracoda.
• marenzelleria Marenzelleria spp.
• monoporeira Monoporeia affinis.
• chironimadae Chironomidae.
• oligochaete Oligochaeta.
• theodoxus Theodoxus fluviatilis.
• sinelobus Sinelobus sp.
• harmothoe Bylgides sarsi.

Each taxon column holds abundance (ind. m⁻²) or biomass (g m⁻²) depending on the value of parameter for that row.

Community_sizes.csv

Number of variables: 42 Number of cases/rows: 848 Missing data codes: blank cell (each row has up to 32 size measurements depending on amount)

• sample_date Date material was sampled (dd/mm/yyyy).
• season Season.
• phase Experimental phase.
• treatment Control or MHW.
• id Replicate core number.
• sediment_depth (cm) Sediment depth layer, as in Community.csv.
• species Taxon measured (Macoma balthica).
• size_av (mm) [length] Mean shell length of individuals in this sample.
• size_median (mm) [length] Median shell length of individuals in this sample.
• amount Number of individuals measured in this sample.
• size1-size32 (mm) [length] Shell length of each individually measured specimen (one column per individual, unused columns left blank).

PW_OM_nutrients_depth_profile.csv

Number of variables: 9 Number of cases/rows: 675 Missing data codes: none

• season Season.
• date Date (yyyy-mm-dd).
• phase Experimental phase (Acclimation, MHW_1, MHW_2, MHW_3).
• treatment Control or MHW.
• depth (cm) [length] Sediment depth of the porewater/organic matter sample.
• parameter Measured variable: OM_LOI (organic matter, loss on ignition), NH4_N, NO3.NO2_N, PO4_P, or Si.
• value Measured value in original units: percent for OM_LOI, µmol L⁻¹ (as N, N, P, or Si respectively, converted from µg L⁻¹ by dividing by the element's molar mass) for NH4_N, NO3.NO2_N, PO4_P, and Si.
• phase_alpha Numeric sequence index of the sampling occasion within season, used only for figure transparency scaling.
• value_mmol (mmol L⁻¹) [concentration] Measured value converted to mmol L⁻¹ (unchanged, i.e. still percent, for OM_LOI).

Seasonal_MHW_nutrients.csv

Number of variables: 14 Number of cases/rows: 306 Missing data codes: none

• season Season.
• date Date (dd/mm/yyyy).
• datetime Date and time of sampling.
• sampling Incubation identifier.
• phase Experimental phase.
• treatment Control or MHW.
• replicate Replicate core number.
• timepoint Start or End of the incubation.
• oxygen (mg L⁻¹) [concentration] Dissolved oxygen concentration.
• nh4_n (µmol L⁻¹) [concentration] Ammonium concentration, as N (converted from µg L⁻¹ NH4 by dividing by the molar mass of N, 14.0067 g mol⁻¹).
• no3_no2_n (µmol L⁻¹) [concentration] Combined nitrate and nitrite concentration, as N (converted from µg L⁻¹ by dividing by the molar mass of N, 14.0067 g mol⁻¹).
• po4_p (µmol L⁻¹) [concentration] Phosphate concentration, as P (converted from µg L⁻¹ PO4 by dividing by the molar mass of P, 30.974 g mol⁻¹).
• si (µmol L⁻¹) [concentration] Dissolved silicate concentration (converted from µg L⁻¹ by dividing by the molar mass of Si, 28.0855 g mol⁻¹).
• water_volume (L) [volume] Incubation chamber water volume, used to calculate flux rates.

Fluxrates.csv

Number of variables: 8 Number of cases/rows: 765 Missing data codes: none

• season Season.
• sampling Incubation identifier.
• phase Experimental phase.
• treatment Control or MHW.
• replicate Replicate core number.
• rate_raw Flux rate before unit standardisation; mg O₂ m⁻² d⁻¹ for oxygen, µmol m⁻² d⁻¹ for nutrients (see parameter).
• parameter Which flux the row describes: Oxygen_mg.L, NH4_N, NO3.NO2_N, PO4_P, or Si.
• rate_mmol (mmol m⁻² d⁻¹) [flux] Flux rate standardised to mmol m⁻² d⁻¹.

Code availability

R scripts used to process these files and reproduce all figures and tables are provided in the accompanying code repository, archived at https://doi.org/10.5281/zenodo.21504698.

Comments

CoastClim

This is a contribution from the Centre for Coastal Ecosystem and Climate Change Research. CoastClim is a multidisciplinary strategic partnership between Stockholm University and the University of Helsinki, that evaluates the links between coastal biodiversity, carbon cycling, and climate feedbacks.

Funding

This study was supported by the Walter and Andrée de Nottbeck Foundation. This study used research infrastructure facilities at Tvärminne Zoological Station, University of Helsinki, as part of FINMARI (Finnish Marine Research Infrastructure Consortium).

Project

This dataset was developed within CoastClim (Centre for Coastal Ecosystem and Climate Change Research)(www.coastclim.org). Funded by the Walter and Andrée de Nottbeck Foundation. Research infrastructure provided by Tvärminne Zoological Station, University of Helsinki, as part of FINMARI (Finnish Marine Research Infrastructure Consortium).

Publisher

Bolin Centre Database

License

Creative Commons Attribution 4.0 International License (CC BY 4.0)

First name

Norman

Last name or organisation

Göbeler

Email address

norman.gobeler@helsinki.fi

Address

Tvärminne Zoological Station, University of Helsinki

Postal code

10900

City

Hanko

Country

Finland

GCMD science keyword

Earth science > Biosphere > Aquatic ecosystems > Benthic habitat

GCMD location

Continent > Europe > Northern Europe > Scandinavia > Finland

Dataset language

English

Begin date

2021-01-11

End date

2021-12-01

DOI

Time

Versions

• 1 2026-09-15T09:21:20.031+00:00
• 1 2026-07-27T09:51:09.225+00:00