Climate-related drivers of estuarine macrobenthic functional redundancy and resilience

• Long-term data (22 yrs) was used to evaluate estuarine functional change. • Macrobenthic functional responses to environmental change were investigated. • SST and sediment muddiness significantly increased over time. • Functional metrics were influenced by SST, SOI, OM and mud content. • Functional Richness and Functional Redundancy indicated increasing levels of community resilience over time. Elevated anthropogenic CO 2 emissions are warming the planet, although our understanding of how climate-related changes manifest locally remains poor. In estuaries, rising air and sea surface temperatures, increased sediment loading, and climate-related changes (e.g., cyclones, heatwaves, droughts) can collectively influence tidal flat biota and the key ecosystem functions they mediate. Here, we used long-term data from six sites in a New Zealand estuary (all sampled quarterly for 22 years) to evaluate tidal flat macroinvertebrate changes and responses of five functional diversity metrics (i.e., Functional Richness, Evenness, Dispersion, Divergence, and Redundancy) to shifting environmental conditions. Sea surface temperature (satellite SST records), sediment organic matter content (OM), and bed sediment muddiness all increased significantly at all sites from 2000-2022. The individual effects of these environmental drivers on functional diversity metrics were mixed, but net trends in Functional Richness and Functional Redundancy indicated increasing levels of community resilience over time. Heat spikes can cause thermal stress, but gradual warming may elevate metabolic rates and accelerate reactions such as photosynthesis. The positive effects on increased food supply (OM) could have outweighed negative influences of increasing mud, generating the net trends in our data. Overall, our research suggests that some estuarine soft-sediment macroinvertebrate communities, based on the analysis of functional diversity metrics, are becoming increasingly resilient and adaptable, rather than increasingly depauperate and functionally impacted, as climate change strengthens.