Competency time and settlement preferences of zoospores of Ulva fenestrata habiting the mid intertidal

Abstract

Macroalgae are increasingly being considered as an important factor in natural ecosystems and in economies around the world. Ulva is one such genus that provides various ecosystem services to humans and marine environments. Within marine ecosystems Ulva is a primary producer, providing direct nutrition for herbivores such as sea urchins and snails, and creates vital habitat structures for juvenile and larval organisms. Ulva can be both a cost and a prize to our economies as is both a significant component of the aquaculture industry and a major source of marine biofouling. Ulva zoospores have been known to settle due to bacterial cues and have an observed distribution primarily in the mid to low intertidal. This study attempted to quantify settlement of the quadriflagellate zoospores of Ulva fenestrata on bacterial biofilms from a variety of tidal heights. The goal was to ascertain if bacterial assemblages specific to tidal height were an impacting settlement factor. Competency time was also investigated to ascertain how long Ulva fenestrata zoospores remain motile. All bacterial biofilms were found to have equal recruitment, with no statistical differences in spore settlement. Zoospores were found to remain motile for up to three hours and 30 minutes with some variability. These findings indicate that observed distributions of Ulva fenestrata are due to some nonbacterial settlement cue or outside pressure and opens up further research questions into the nature of this cue.