Benthic estuarine communities' contribution to bioturbation under the experimental effect of marine heatwaves

Abstract

Marine heatwaves are increasing worldwide, with several negative impacts on biological communities and ecosystems. This 24-day study tested heatwaves' effect with distinct duration and recovery periods on benthic estuarine communities' diversity and contribution to ecosystem functioning experimentally. The communities were obtained from a temperate estuary, usually subjected to high daily thermal amplitudes. Our goal was to understand the communities' response to the thermal change, including the community descriptors and behavioural changes expected during heat extremes. We measured community composition and structural changes and the bioturbation process and nutrient release as ecosystem functioning measurements. Overall, our findings highlight the potential tolerance of studied estuarine species to the temperature ranges tested in the study, as community composition and structure were similar, independently of the warming effect. We detected a slight trend for bioturbation and nutrient release increase in the communities under warming, yet these responses were not consistent with the heatwaves exposure duration. Overall, we conclude on the complexity of estuarine communities’ contribution to functioning under warming, and the importance of scalable experiments with benthic organisms' responses to climate variability, accommodating longer time scales and replication. Such an approach would set more efficient expectations towards climate change mitigation or adaptation in temperate estuarine ecosystems.

Changes in macrofauna bioturbation during repeated heatwaves mediate changes in biogeochemical cycling of nutrients

“…In contrast to our results, results from earlier studies indicate a lack of effects of short-term, moderate MHWs (e.g. Crespo et al, 2017;Dolbeth et al, 2021). These studies were, however, conducted on intertidal estuarine populations, naturally subject and adapted to higher and more frequent daily variations of temperature and could therefore tolerate the changes induced by the simulated heatwave (Dolbeth et al, 2021).…”

“…the RGB levels). Three metrics were then calculated, characterizing the intensity of the particle mixing performed by the whole community, namely the mean (meanPD), the median (medPD) and the maximum (maxPD) penetration depth of luminophores in the sediment column (Crespo et al, 2017;Dolbeth et al, 2021). For each box, meanPD and medPD measured in the four sides of each box were averaged and the maximum maxPD measured in the four sides was kept.…”

“…The influence of benthic animals on biogeochemical cycling of nutrients at the seafloor is context-dependent, and is therefore likely to be affected by changes in environmental conditions following climate change (Solan et al, 2004). Only a few studies have looked at the effects of heatwaves on the bioturbation of macrofauna and tried to link that to ecosystem functioning (see Crespo et al, 2017;Dolbeth et al, 2021;Kauppi & Villnäs, 2022) despite the pivotal role this plays in the functioning of marine ecosystems. However, the results of these studies have been somewhat inconclusive with no clear effect on bioturbation due to context-dependent responses and/ or the methodology used.…”

Marine heatwaves of differing intensities lead to distinct patterns in seafloor functioning

“…For example, Dolbeth et al . [ 29 ] found a slight increase in bioturbation and release of nutrients from the sediment under an experimentally induced heatwave.…”

“…Although severe changes in the structure of biological communities have been observed in heatwave-impacted ecosystems globally, and both chemical and physiological processes are temperature dependent [2,13], there are only few studies exploring impacts of MHWs on functioning at the ecosystem level. For example, Dolbeth et al [29] found a slight increase in bioturbation and release of nutrients from the sediment under an experimentally induced heatwave.…”