Vertical distribution of spores of blade-forming Sarcothalia crispata (Gigartinaceae) and crustose corallines (Corallinaceae) in the water column

Abstract

Changes in spore abundance of the blade-forming Sarcothalia crispata and crustose coralline seaweeds were determined to relate height above the substratum at which propagules are liberated with their dispersal potential. Recruit density was quantified on artificial substrata at the surface of the water column, mid-water, and seafloor. Spore abundance was determined in water samples obtained at the same levels during periods of calm and rough seas. Spore density was also determined along a transect running perpendicularly to the shore. Density of recruits S. crispata increased with depth, whereas coralline recruits were abundant at the seafloor level. During calm seas, spore density of S. crispata and crustose corallines increased with depth, but the latter were more variable. During rough seas, spore density was very high; spores of S. crispata increased toward the surface, or were homogenous in the water column, whereas distribution of crustose coralline spores was more variable. Finally, density of crustose coralline spores decreased more abruptly with distance from the shore than that of the bladed species. These results strongly suggest that the height at which spores are released (a correlate of algal morphology) influences spore distribution in the water column and the dispersal potential.