The capacity for motility is important for many micro-organisms, and also for macroalgal spores, because it can allow them to explore a physically and chemically heterogeneous environment and react to the perceived information by movement towards favourable conditions or away from hazardous conditions, The swimming behaviour of spores of the brown alga Hincksia irregularis was analysed using computer-assisted motion analysis. We distinguished five main swimming patterns: straight paths, search circles, orientation, gyration and wobbling. Different functions can be suggested for different swimming patterns in the context of spore settlement. Straight paths may be important in small-scale movements in the benthic boundary layer to locate suitable microenvironments. Gradients in chemical or physical parameters may be detected during search circles, and orientation should facilitate the detection of the structure of surfaces. Gyration occurs during the initial reversible phase of spore adhesion, which can ultimately lead to settlement. Wobbling patterns do not appear to be associated with settlement and may typify irritated or mechanically damaged spores. The dominant swimming pattern changed with spore age (in the period from 10 ± 5 to 60 ± 5 min of spore age), with younger spores swimming primarily in straight lines and search circles, whereas older spores swam in orientation and gyration patterns. These changes in swimming patterns can be quantified using speed (SPD), which decreases over time, and the rate of change of direction (RCD), which increases over time. We suggest that computer-assisted motion analysis is an efficient way to bioassay the influence of environmental factors on spore movements. Reaction to environmental factors can be quantified as changes in SPD and RCD of spore swimming.