Coastal dunes represent priority habitats for conservation due to the provision of valuable ecosystem services such as land protection, water supply or biodiversity conservation. Soil microbial communities are of crucial importance to maintain plant diversity due to harsh environmental conditions, water limitation and nutrient scarcity. Invasive alien plants represent a major threat to ecosystem conservation. Here, we explored different impacts of Carpobrotus edulis, a succulent plant invading coastal areas worldwide, on the function and structure of bacterial communities. Sand represents a challenging substrate due to low organic matter content and limited microbial activity. We optimized bacterial extraction for functional evaluation before assessing ecosystem impacts produced by C. edulis. We compared 12 extracting procedures combining different soil storage, sample amount and extracting solutions on the functional activity of sand communities through the community-level physiological profile. We further explored the function (using Biolog Ecoplates) and structure [using polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE)] of bacterial communities from dunes invaded by C. edulis. Saline solution consistently increased bacterial cells detected by cytometry (P ≤ 0.001). Principal component analysis suggested a limited temporal framework (0–24 h) in which community function can be explored without significant alterations in C substrate consumption. Changes under C. edulis invasion exhibited a different pattern of C substrate utilization comparing native and non-native zones (interspecific), but also between native zones (intraspecific), suggesting that functional impacts are site-dependent. Complementary, results obtained from PCR-DGGE indicated that the bacterial community structure of native dunes significantly differed from dunes invaded by C. edulis.