Effect of water movement and substratum type on vegetative recruitment of the invasive green alga Codium fragile ssp. tomentosoides

We examined the ability of vegetative propagules (small buds and branch fragments) of the green alga Codium fragile ssp. tomentosoides to attach and grow on natural substrata in laboratory and field experiments. In the laboratory, the probability of attachment (on coralline algae, mussel shell, smooth and rough rock) was greater for buds than excised apical branches (both ∼4 cm long) over 10 weeks, and greater in weak flow (1.3 cm s^-1) than static conditions. Probability of attachment differed among substrata in flow (greater on coralline algae than smooth rock) but not static conditions. Attachment strength in flow was greater for buds than fragments (pooled over substrata). Growth was greater for fragments than buds in static conditions, but not in flow. Fragments grew more in static conditions than in flow. In a field experiment, buds were transplanted to three tide pools at different tidal heights on a rocky shore. After eight months, the proportion that attached and attachment strengths of transplants did not differ significantly among pools. However, transplants in the high pool grew less and were discolored and atypically branched compared to those in pools lower on the shore. These findings indicate that vegetative propagation may contribute to the invasive success of Codium fragile.