In: Invertebrates: Classification, Evolution and Biodiversity ISBN: 978-1-62618-789-4 Editor: Rafael Riosmena-Rodriguez © 2013 Nova Science Publishers, Inc. Chapter 4 Invertebrates: St ' ructure of the Community and Biodiversity Associated to Rhodolith- Sponge Complex at Magdalena Bay. South Baja California Pamela Herrera- Martinez· I , Sergio Alvarez-Hernandez Ia , Maria del Carmen Mendez-Trejo2,3 and Rafael Riosmena-Rodriguei IDepartamento de Hidrobiologfa, Universidad Aut6noma Metropolitana-Iztapalapa, Mexico I"Laboratorio de Ficologfa Aplicada, Departamento de Hidrobiologfa, Universidad Aut6noma Metropolitana- Iztapalapa, Mexico 2Programa de Investigaci6n en Botanica Marina, Departamento de Biologfa Marina, Universidad de Baja California Sur. La Paz, Baja California Sur, Mexico 3Centro de Investigaci6n Cientffica del Mar (CIClMAR), Instituto Politecnico Nacional, La Paz, Baja California Sur, Mexico Abstract One of the most exceptional and multifunctional habitats for cryptic and epibenthic fauna has been established in the costal zones of Magdalena Bay conforming an interesting interaction between rhodoliths and marine sponges. These function primarily as refuges, where the rhodolith beds (red coralline algae) grow in association with a high biodiversity of marine sponges and form functional complexes to counteract the hydrodynamic effect generated by the current flow. The main objective in this chapter was to highlight the community structure of cryptic, epibenthic, and sessile fauna with a multifactorial analysis including: the ecological analysis via alpha diversity, the • Email address:herrera .maninez.pamel@gmail.com.