Fall 2015

Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)


Moss Landing Marine Laboratories


Rhodoliths (Corallinaceae, Rhodophyta) are unattached, branching, calcareous red algae that are important foundation species in near shore marine systems. Aggregations, or beds, produce habitat that is a mixture of hard substrate and soft sediment supporting diverse assemblages of both crypto- and macrofauna. At Catalina Island, CA (33º44’55”N, 118º50’22”W), beds of relatively small rhodoliths were recently documented within several bays and coves. To better understand the associated community, this study describes the cryptofaunal invertebrate assemblages associated with live rhodolith (LR), dead rhodolith (DR) and sand (S) habitats within three sites (Cherry Cove, Isthmus Harbor, Avalon Harbor). Motile invertebrates (> 0.5 mm) were removed from sediment cores, identified to lowest certain taxonomic level and enumerated. Percent dry weight of eight size classes of sediment and percent dry weight of live rhodoliths were calculated. All three habitats had different sediment compositions with LR and DR habitats being more similar to each other than to S. Of the 184 morphotypes found across all habitats and sites, 142 were within LR, 109 within DR and 91 within S. LR hosted greater mean abundance of invertebrates (479.4 ± 42.0 ind./core) and greater mean taxonomic richness (43.3 ± 2.3 taxa/core) than either DR (226.5 ± 34.0 ind./core, 26.8 ± 1.2 taxa/core) or S (152.7 ± 17.3 ind./core, 24.3 ± 1.5 taxa/core) across all sites. Invertebrate community composition differed by habitat with LR and DR supporting slightly different communities that more strongly differed from S. Community composition differed significantly by site within S (ANOSIM, R = 0.968, p 4750 μm) in the substrate explained more variation in invertebrate abundance and taxonomic diversity than percent dry weight of live rhodolith material (live only, > 500 μm) suggesting that physical structure provided by intact rhodoliths has an influence on the associated invertebrate assemblages. This study demonstrates that despite their small size (< 2 cm) the rhodolith beds at Catalina Island support an abundant and diverse invertebrate community. Further research will help identify the mechanisms supporting the observed rhodolith associated invertebrate diversity identified in this study.