Qualitative and quantitative studies of the swimming behaviour of Hincksiairregularis (Phaeophyceae) spores: ecological implications and parameters for quantitative swimming assays

The capacity for motility is important for many micro-organisms, and also f or macroalgal spores, because it can allow them to explore a physically and chemically heterogeneous environment and react to the perceived informatio n by movement towards favourable conditions or away from hazardous conditio ns. The swimming behaviour of spores of the brown alga Hincksia irregularis was analysed using computer-assisted motion analysis. We distinguished fiv e main swimming patterns: straight paths, search circles, orientation, gyra tion and wobbling. Different functions can be suggested for different swimm ing patterns in the context of spore settlement. Straight paths may be impo rtant in small-scale movements in the benthic boundary layer to locate suit able microenvironments. Gradients in chemical or physical parameters may be detected during search circles. and orientation should facilitate the dete ction of the structure of surfaces. Gyration occurs during the initial reve rsible phase of spore adhesion, which can ultimately lead to settlement. Wo bbling patterns do not appear to be associated with settlement and may typi fy irritated or mechanically damaged spores. The dominant swimming pattern changed with spore age (in the period from 10 +/- 5 to 60 +/- 5 min of spor e age), with younger spores swimming primarily in straight lines and search circles. whereas older spores swam in orientation and gyration patterns. T hese changes in swimming patterns can be quantified using speed (SPD), whic h decreases over time, and the rate of change of direction (RCD), which inc reases over time. We suggest that computer-assisted motion analysis is an e fficient way to bioassay the influence of environmental factors on spore mo vements. Reaction to environmental factors can be quantified as changes in SPD and RCD of spore swimming.