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

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.