Description
The invasive brown macroalga, the devil weed, Sargassum horneri, has spread along the southern California coast, replacing the native habitat-forming macroalga, the giant kelp, Macrocystis pyifera. M. pyrifera is a critical habitat for algal-associated fishes, especially for the arrival and survival of juvenile fish that constitutes recruitment success. It is unclear whether critical processes in recruitment may be altered if S. horneri replaces M. pyrifera as the dominant biogenic habitat on rocky reefs. Through a series of laboratory experiments, I investigated the effects of algal identity on post-settlement processes contributing to recruitment success for a common macrophyte-associated fish, the giant kelpfish, Heterostichus rostratus. To evaluate the potential impacts of S. horneri vs. M. pyrifera in their effects on juvenile giant kelpfish I explored whether there were differences in their (1) habitat choice in the presence of both macroalgae, (2) prey choice employing the mysid shrimp, H. costata, that were fed on either of the two macroalgae, and (3) predator-mediated mortality by a common piscivore in both macroalgal habitats. The results of these experiments suggest that, at least for the post-settlement processes evaluated here, algal identity does not appear to have a significant impact on giant kelpfish, and recruitment success in S. horneri may be equivalent to that observed in M. pyrifera. It is also possible, however, that differential settlement to these macroalgae or other post-settlement factors may play a role in facilitating recruitment success within these habitats.
