REPORT Peter J. Mumby Æ Nicola L. Foster Elizabeth A. Glynn Fahy Patch dynamics of coral reef macroalgae under chronic and acute disturbance Received: 25 June 2004 / Accepted: 20 September 2005 / Published online: 10 November 2005 Ó Springer-Verlag 2005 Abstract The patch dynamics (colonisation rate, growth rate, and extinction rate) are quantified for two domi- nant species of macroalgae on a Caribbean forereef in Belize: Lobophora variegata (Lamouroux) and Dictyota pulchella (Ho¨rnig and Schnetter). Measurements were taken on time scales of days, weeks, months, and years during which three hurricanes occurred. All patches were followed on naturally occurring ramets of dead Montastraea annularis. The first hurricane (Mitch) caused massive coral mortality and liberated space for algal colonisation. The cover of Lobophora increased throughout the study and herbivores did not appear to limit its cover within a 4 year time frame. In contrast, the cover of D. pulchella fluctuated greatly and showed no net increase, despite an increase in parrotfish biomass and settlement space. Variation in the overall percent cover of an alga is not indicative of the underlying patch dynamics. The steady rise in the cover of Lobophora took place despite a high turnover of patches (12–60% of patches per year). The patch dynamics of Dictyota were slower (7–20%), but a greater patch density and threefold higher lateral growth rate led to greater fluc- tuations in total cover. The dynamics of algal patches are size-specific such that larger patches are less likely to become extinct during hurricanes. Keywords Macroalgae Æ Coral Æ Hurricane Æ Patch dynamics Æ Competition Æ Herbivory Introduction Fleshy macroalgae play a fundamental, albeit incom- pletely understood, role in the dynamics and functioning of coral reefs (Steneck and Dethier 1994). First, these reef algae (hereafter referred to simply as macroalgae) pre-empt settlement space that might otherwise be available for settling coral planulae. Second, there is growing evidence that scleractinian corals compete for space with macroalgae (de Ruyter van Steveninck et al. 1988b; Tanner 1995; Jompa and McCook 2002a, 2003). The outcome of such competition includes a decline in the growth rates of both competitors (de Ruyter van Steveninck et al. 1988b; Jompa and McCook 2002a), reductions in the fecundity of corals (Tanner 1995), and even coral mortality (Bak and Engel 1979; Hughes and Tanner 2000; Lirman 2001). A wide variety of distur- bance phenomena may result in a change (usually an increase) in the biomass of macroalgae on coral reefs. Such impacts include drastic reductions in urchin den- sity brought about by either disease or removal of pre- dators (Carpenter 1990; Hughes 1994; McClanahan et al. 1996), overfishing of herbivorous fish (Hughes 1994; McClanahan 1997), coral mortality from mass bleaching (Diaz-Pulido and McCook 2002), and rising nutrients (Littler et al. 1993). Unfortunately, reefs dominated by macroalgae tend to support detrital tro- phic pathways, rather than those associated with high levels of secondary and tertiary production and fisheries (Carpenter 1990). Whilst the cover of macroalgae is a core component of most reef monitoring programmes (Rogers et al. 1994; English et al. 1997), such studies rarely, if ever, investi- gate the dynamics of algae at the scale of individual patches. Indeed, we have found few accounts of algal patch dynamics in the coral reef literature (exceptions include de Ruyter van Steveninck and Breeman 1987a, b, 1988a; Stiger and Payri 1999). Patch dynamics have great ecological importance, particularly when consid- ering processes of coral recruitment and coral–algal Communicated by Biological Editor K. Sullivan Sealey P. J. Mumby (&) Æ N. L. Foster Marine Spatial Ecology Laboratory, School of BioSciences, University of Exeter, Prince of Wales Road, Exeter, EX4 4PS, UK E-mail: p.j.mumby@ex.ac.uk Tel.: +44-1392-263798 Fax: +44-1392-263700 E. A. G. Fahy Nova Southeastern University Oceanographic Center, 8000 N Ocean Drive, Dania, FL, 33004, USA Coral Reefs (2005) 24: 681–692 DOI 10.1007/s00338-005-0058-5