Coral Reefs (2008) 27:389–393 DOI 10.1007/s00338-007-0346-3 13 NOTE Long-term dynamics of the brown macroalga Lobophora variegata on deep reefs in Curaçao M. M. Nugues · R. P. M. Bak Received: 28 March 2007 / Accepted: 4 December 2007 / Published online: 18 December 2007  Springer-Verlag 2007 Abstract Lobophora variegata occurs in the eulittoral zone and in deep water on coral reefs in Curaçao. An analysis of the long-term (1979–2006) changes in the vertical distri- bution of the macroalga in permanent quadrats indicated a signiWcant increase in cover of the deepwater community. In 1998, Lobophora covered 1 and 5% of the quadrats at 20 and 30 m, respectively. By 2006, these values had risen to 25 and 18%, precipitating a shift in abundance of corals and macro- algae at both depths. This increase coincided with losses in coral cover, possibly linked to bleaching, disease and storm- related mortality in deep water plating Agaricia corals. In contrast, macroalgae remained relatively rare (<6% cover) on shallower (10 m) and deeper (40 m) reefs despite declines in coral cover also occurring at these depths, illustrating the depth-dependent dynamics of coral reefs. Several hypotheses are suggested to explain these changes. Keywords Coral mortality · Coral bleaching · Deep coral reef · Herbivory · Macroalgae · Phase shifts Introduction Coral reefs have experienced widespread ecological changes during the last decades. Coral cover and diversity have declined, while, in many areas, the cover and biomass of macroalgae have increased (Hughes et al. 2003). The causes of these changes remain highly controversial. Coral bleaching, diseases, nutrient enrichment and overWshing appear to be major factors (Precht and Aronson 2006). However, studies over broad spatial and temporal gradients are lacking (Hughes et al. 2003). In particular, deep (>20 m) coral reef communities have been neglected from the majority of long-term studies documenting shifts to algal dominance. These communities have been considered to be relatively stable due to their seemingly constant phys- ical conditions and protection against many of the anthro- pogenic stressors impacting shallow reefs (Bak et al. 2005). The brown foliose macroalga Lobophora variegata (J. V. Lamouroux) Womersley ex E. C. Oliveira is distributed worldwide in tropical and warm temperate seas. This mac- roalga has increased on many degraded reefs (e.g., Mumby et al. 2005), and poses a threat to coral populations by overgrowing adult colonies, reducing growth rates and inhibiting recruitment (Nugues and Bak 2006). In 1975, Lobophora showed a discontinuous vertical distribution pattern, forming two distinct belts: one in the eulittoral community and one in deep water on coral reefs in Cura- çao, Netherlands Antilles (van den Hoek et al. 1978). In this study, long-term (1973/1979–2006) changes in the ver- tical distribution of the deep water Lobophora population and other benthic components were studied using a series of photographs of permanent quadrats distributed along a broad (10–40 m) depth gradient in Curaçao. Materials and methods The abundance of L. variegata and other benthic organisms was surveyed from permanent quadrats established in 1973 Communicated by P. J. Mumby. M. M. Nugues (&) · R. P. M. Bak Royal Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands e-mail: mnugues@nioz.nl R. P. M. Bak University of Amsterdam, IBED, P.O. Box 94766, 1090 GT Amsterdam, The Netherlands