Publication Date

Spring 2025

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Moss Landing Marine Laboratories

Advisor

Amanda Kahn; Bruno Pernet; Diana Steller; Scott Hamilton

Abstract

Rhodolith beds are globally distributed hotspots of diversity and productivity and serve as nursery habitats for some marine invertebrates. Poorly understood is whether rhodolith beds are nurseries because invertebrate larvae actively select them for settlement or migrate to them at later life stages. We studied the nursery role of rhodolith beds for the painted urchin, Lytechinus pictus at Santa Catalina Island, CA, USA. Subtidal surveys showed that in areas with greater live rhodolith cover, urchin density increased as well as mean urchin size. In caged substrate choice experiments, urchins selected rhodolith substrate relative to carbonate sand, supporting the notion that urchins congregate in rhodolith beds after they have settled. To evaluate whether beds also serve as nurseries by inducing settlement, urchin larvae were assessed following exposure to six cues: live and dead rhodolith, biofilm-inoculated sand, GABA, KCl, and filtered seawater. Live rhodolith induced the strongest settlement response across all treatments, initiating 2.5x greater settlement compared to the inducement control of KCl after 24 hours. Larvae also settled faster in the presence of live rhodolith substrate than other treatments. These results highlight the importance of rhodolith beds for multiple life stages of L. pictus, by inducing settlement of larvae and supporting post-larval individuals. Rhodolith beds receive minimal protections globally, due to limited research on their ecological importance. However, recognizing their role as nursery habitats strengthens the case for the inclusion of rhodolith beds in future management decisions.

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