Crab burrow morphology modulates vertical soil hydrological connectivity in saltmarshes: a field experimental study

• Soil properties and vegetation density shaped crab burrow distribution in salt marshes. • Precise resin casting of crab burrows shows high variability in their morphology in salt marshe. • Crab burrows amplify groundwater responses to surface water dynamics by enhancing preferential flow. • Soil porosity, burrow diameter and length served as indicators of stronger vertical hydrological connectivity. Semi-terrestrial crabs, widely regarded as “ecosystem engineers”, play a crucial role in modifying soil environments through their daily activities in salt marshes, and thier burrows are an important component of soil biogenic structures. Understanding the distribution and morphological characteristics of these burrows is essential for quantifying their influence on soil ecological functions, and for informing effective management strategies in salt marsh ecosystems. In this study, we conducted field investigations on burrow distribution and morphological characteristics in a typical salt marsh of the Yellow River Delta, and analyzed the environmental factors influencing burrow patterns. Based on hydrological monitoring, we used a Surface water − Groundwater Coupling Index (SGCI) to quantify vertical hydrological connectivity and assessed the influence of crab burrows and soil properties on the SGCI. Results showed that crab burrow distribution exhibited spatial heterogeneity. Burrow density tended to increase with lower soil bulk density and total carbon content, and with higher soil saturated water content and vegetation density. In the supratidal zone, burrow density was lower, while burrows in the subtidal zone tended to be smaller in morphology. Total soil porosity, burrow opening diameter, burrow neck diameter, and the curved length from opening to the chamber were identified as sensitive indicators altering soil vertical hydrological connectivity. These results deepened our understanding of soil structure–function relationships, offering a valuable reference for future research on biota-environment interactions and their role in shaping salt marsh ecosystem functioning.