What Drives Ecological Recovery? Identifying Key Factors of Benthic Faunal Restoration After Invasive <em>Spartina alterniflora</em> Removal

Restoring an ecosystem after a biological invasion is a huge challenge. A key question for ecologists is whether it can truly bring back what was lost. In coastal areas, the invasive cordgrass Spartina alterniflora is a major problem. It takes over tidal flats, changing the very structure of the sediment and devastating the small creatures—the macrobenthos—that live within it. This, in turn, disrupts the food supply for migrating waterbirds that depend on these flats. While digging up the invasive grass is a common solution, we still don't fully understand what drives the recovery. Does the habitat bounce back because the physical environment is fixed, or is it because the food sources (nutrients) return? To figure this out, we ran a field study in Hangzhou Bay, an area known for its large tides. We compared three different zones: patches of the invasive Spartina, mudflats where native Scirpus mariqueter sedge was restored after clearing the invader, and untouched native mudflats. We simultaneously tracked changes in the sediment's physical makeup (like porosity, water content, and grain size), its nutritional content (organic matter), and the community of bottom-dwelling creatures. Using a combination of Gradient Boosting Decision Trees (XGBoost) and SHAP analysis to sort through the data, we found that removing the invasive grass worked. The median number of species jumped from 5 to 9, and the total biomass shot up from a meager 1.36 to 11.75 g/m².Interestingly, this comeback was directly tied to improvements in the sediment's physical condition. After removal, total porosity increased by 19%, water content went up by nearly 11%, and the fraction of coarser particles grew by over 41%. The SHAP analysis confirmed what we saw: total porosity and water content were the most important factors predicting recovery (SHAP importance: 0.106 and 0.082). Their influence was more than double that of organic matter (0.041).What this tells us is that, at least in Hangzhou Bay, fixing the physical structure of the habitat is the first and most critical step. Rebuilding the sediment foundation kickstarts the return of the native benthic community, more so than any immediate change in nutrient levels. Our work shows that successful coastal restoration hinges on getting the physical substrate right first, giving managers a clearer target for assessing and managing invaded wetlands.