MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 387: 147–156, 2009 doi: 10.3354/meps08097 Published July 28 INTRODUCTION A basic principle of restoration ecology is that pri- mary successional processes can be accelerated by prudent interventions to physico-chemical and/or biotic attributes of a degraded ecosystem (Hobbs & Norton 1996, Dobson et al. 1997). Enhancement of physical habitat structure is a promising intervention in aquatic systems because of its importance in mediat- ing ecological processes. For example, physical struc- ture affects hydrodynamic conditions such as flow and boundary layer dynamics, as well as potential expo- sure to anoxia, both of which can influence feeding, metabolism, and recruitment of benthic organisms (Genin et al. 1986, Lenihan 1999, Carbindale et al. 2002). Physical structure and heterogeneity are also important to ecosystem function in providing habitat for associated fauna, thereby controlling trophic inter- actions including crucial herbivory processes in coral reef systems (Gladfelter & Gladfelter 1978, Lindahl et al. 2001, Grabowski & Powers 2004, Lee 2006). Indeed, because coral reef biodiversity (e.g. Jones et al. 2004), ecological services (Moberg & Folke 1999), and aesthetic values are largely owed to architectural © Inter-Research 2009 · www.int-res.com *Email: margaret.w.miller@noaa.gov Alternate benthic assemblages on reef restoration structures and cascading effects on coral settlement M. W. Miller 1, * , A. Valdivia 2 , K. L. Kramer 2, 4 , B. Mason 3 , D. E. Williams 2 , L. Johnston 3 1 NOAA-Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Beach Dr., Miami, Florida 33149, USA 2 Cooperative Institute of Marine and Atmospheric Science, and 3 Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy, Miami, Florida 33149, USA 4 Present address: National Park Service, Pacific Island Network Inventory and Monitoring (PACN I&M) PO Box 52 Hawai’i National Park, Hawaii 96718, USA ABSTRACT: In coral reefs, restoration actions often involve artificial construction since physical structure enhances physico-chemical conditions for benthic communities and provides habitat for reef-associated fauna. We evaluated the performance of 4 restoration structures (RS, aged 5 to 12 yr) by comparing convergence of their benthic assemblages to adjacent reference reefs (REF). Multivari- ate clustering indicated that benthic assemblages were significantly distinct between RS and REF, as well as among sites. Differences were primarily attributable to weedy macroalgal and cyanobacterial groups, not slow-growing corals and crustose coralline algae. RS had a higher abundance of cyanobacterial turfs that can negatively affect adult and larval corals. To elucidate potential cascad- ing effects on reef development, we tested whether exudates of the distinct RS and REF assemblages inhibit settlement by planulae of 3 coral species in laboratory assays. Relative settlement deterrence (versus seawater controls) was variable both between sites and among coral species. For example, both RS and REF exudates from one site were deterrent to settlement for Acropora palmata and Diploria strigosa, but, for Montastraea faveolata, RS (but not REF) exudates from a second site were deterrent, while RS exudates from the first site were not. Overall, results indicate that divergence of benthic assemblages is not simply attributable to incomplete succession, but appears to be a persistent, possibly stable state and that benthic algal/cyanobacterial assemblages on both RS and REF in these locations impair ‘recruitment potential’ for framework-building corals to some degree. KEY WORDS: Coral larvae · Cyanobacteria · Acropora palmata · Montastraea faveolata · Diploria strigosa · Succession · Florida Keys Resale or republication not permitted without written consent of the publisher