Nutrients do not influence swimming behavior or settlement rates of Ectocarpus siliculosus (Phaeophyceae) spores

Spores newly released from plurilocular sporangia of Ectocarpus siliculosus (Dillw,) Lyngb. sporophytes were assayed for chemotaxis to nutrients and f or settlement stimulation by nutrients. To enable these measurements with r elatively small volumes and numbers of released spores, we developed a comp uter-assisted motion-analysis assay for spore chemotaxis and verified the r esults with a more standard, capillary tube chemotaxis assay. The presence of a nutrient gradient did not influence the swimming behavior of E, silicu losus spores in the motion-analysis assay, and likewise no chemotactic effe ct was measured in the capillary tube assay, Microplate settlement assays p reviously utilized with bacteria and invertebrates were adapted for use wit h algal spores, E, siliculosus spores settled at higher rates on a hydropho bic plastic surface than on surfaces with either positively or negatively c harged hydrophilic coating. Nutrient mixtures had no effect on the rate of spore settlement on hydrophobic surfaces.