Temporal variation in seaweed and invertebrate assemblages in shallow rhodolith beds of Baja California Sur, México

We assessed temporal variation (2013–2015) in rhodolith (non-geniculate corallines) size and cover, as well as variability in associated macroalgae and invertebrates in one rhodolith bed from the Gulf of California and two on the Pacific Coast of Baja California Sur, México. While rhodoliths persisted at all sites, those in the Gulf were less abundant (Lithothamnion muelleri: 10–14% cover) compared to Pacific sites (Lithophyllum margaritae: 40–64% cover). Rhodoliths from Pacific sites were influenced by storms and tidal currents that shifted beds and redistributed fine sediments. At the Gulf site, 30 macroalgal taxa were encountered and abundance peaked during spring (76–78% cover) and early summer (73–97% cover), then declined following extreme summer heat (22–25% cover) suggesting algae cycle in response to seasonal temperature changes. At Pacific sites, 14 macroalgal taxa were encountered with highest covers observed in winter 2014 (44%) and spring 2015 (26%). Seasonality was potentially masked by algal blooms or inter-annual temperature variation. Sessile invertebrate cover was low at the Gulf site (typically <7%) and ranged from 3 to 21% at Pacific sites, while mobile invertebrates were dominated by arthropods (Gulf: 1–3 ind m⁻², Pacific: 1–91 ind m⁻²) and molluscs (Gulf: 0–2 ind m⁻², Pacific: 9–470 ind m⁻²). Invertebrate assemblages did not vary seasonally at any site and were likely impacted by episodic recruitment as well as other biotic and abiotic factors. Detailed life history studies and more complete environmental data are needed to better connect relationships between biological patterns observed in rhodolith beds worldwide and associated environmental factors.