Cryptofaunal Diversity in a Southwestern Atlantic Rhodolith Bed—Morphology Effect Versus Depth

Rhodolith beds are ecologically important benthic habitats formed by coralline red algae, found across a wide range of latitudes and depths. They provide crucial ecosystem services, including climate change mitigation and biodiversity support, yet remain understudied. Rhodoliths are known to influence the diversity and abundance of associated cryptofauna through their structural complexity and microhabitat provision. In this study, we examined the cryptofaunal community associated with two rhodolith-forming species, Lithophyllum atlanticum and Melyvonnea erubescens, with distinct growth forms, in a rhodolith bed located at a no-take area in the Southwestern Atlantic. We evaluated the effects of rhodolith structural complexity, depth and seasons on cryptofaunal community composition. Our findings revealed significant differences in cryptofaunal composition between the two species at different depths. Structural characteristics, such as volume and branch density, varied between species and influenced their associated fauna. Depth and season seem to indirectly impact community distribution, as well branch density appears to be the most relevant driver influencing cryptofaunal assemblage differences. Our findings reinforce the ecological importance of rhodolith beds and highlight the need for further research to better understand their conservation and ecological significance. Protecting sensitive rhodolith beds from potential impacts is crucial for preserving biodiversity and ecosystem services. Therefore, any discussion or management changes that impact its conservation status must consider different aspects of its biology as well as its ecological relationships with associated fauna and flora.