Climate change stress causes simplification of a benthic ecosystem network

Anthropogenic climate change is generating multiple stressors that affect coastal seafloor ecosystem functions such as nutrient recycling, primary production, and sediment metabolism. These functions are driven by the ecological traits of resident species interacting with their environment, creating an ecosystem network that supports ecosystem multifunctionality. While multiple stressors are known to impact individual functions or species, our understanding of how climate change impacts broader ecosystem multifunctionality remains limited. To address this, we simulated the effects of sea level rise and storm-derived terrigenous sediment deposition, individually and in combination, on an intertidal sediment ecosystem in Aotearoa New Zealand. We assessed ecosystem functions, environmental characteristics, and macrofauna trait groups and constructed ecosystem networks for each stressor treatment. We found that while individual ecosystem functions alone showed limited change in response to stress compared to control conditions, their connections with environmental characteristics and macrofauna trait groups were altered, indicating network simplification. Sea level rise caused a 33.3 % reduction in the number of network connections, sediment deposition caused a 20 % reduction, and the combined stressors resulted in the greatest simplification, with a 46.7 % reduction. These findings highlight subtle ecosystem responses to stress, revealing a loss of resilience and likely a diminished capacity to withstand further stress. We demonstrate the value of utilising networks to assess multiple stressor effects on ecosystem multifunctionality, an important tool for advancing our understanding and response to the multiple impacts of climate change.