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Data from: Marine heatwaves amplify benthic community metabolism and solute flux in a seafloor heating experiment

Göbeler, Norman1; Kauppi, Laura1; Norkko, Alf1; Norkko, Joanna1

Published Mar 07, 2025 on Dryad. https://doi.org/10.5061/dryad.kd51c5bj0

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Abstract

The magnitude and frequency of marine heatwaves is increasing and predicted to intensify, but our ability to understand the real-world effects on vital benthic ecosystems is lagging behind. Prior insights into the impacts of marine heatwaves are often derived from observational or laboratory studies. Observational studies may not fully disentangle the complexities of potential compound events and typically focus on severe, often lethal marine heatwaves. Laboratory studies on the other hand, while valuable for understanding specific mechanisms, often use artificial setups and can introduce unnatural disturbances that do not reflect real-world scenarios. To investigate sublethal temperature effects of marine heatwaves in a natural benthic habitat, we developed a novel approach for inducing elevated water temperatures in situ over several days. The system utilizes domestic under-floor heating technology combined with custom-made benthic chambers. We placed 10 chambers for 15 days in a bare-sediment habitat at 2.5 m depth and heated 5 chambers to 5°C above ambient water temperatures in summer for 6 days followed by a period of 7 days at ambient temperatures. Incubations during day and night were performed during the experiment to assess changes in ecosystem functioning (solute fluxes) and sediment cores were collected at the end of the experiment to assess the effects of a realistic marine heatwave on benthic community structure. 4. The results indicate that while the benthic community structure remained similar between the treatments, except for a size shift of Marenzelleria spp. towards smaller individuals in the heated treatment, elevated temperatures caused a significant increase in the community respiration and amplified the magnitude of either efflux or influx of nutrients (NH4+-N, PO43--P, Si). Primary production during daytime incubations remained mostly unaffected by the heatwave treatment, contributing to the concept of heterotrophy being more influenced by increased temperature than autotrophy. This study confirms the suitability of the novel system for examining the impact of temperature on benthic habitats in situ and demonstrates its potential for investigation of complex habitats and communities, which is essential for our understanding of the ecosystem-level effects of climate change.