Abstract. Many marine scientists have concluded that coral reefs are moving toward or are locked into a seaweed-dominated state. However, because there have been no regional-or global-scale analyses of such coral reef ''phase shifts,'' the magnitude of this phenomenon was unknown. We analyzed 3581 quantitative surveys of 1851 reefs performed between 1996 and 2006 to determine the frequency, geographical extent, and degree of macroalgal dominance of coral reefs and of coral to macroalgal phase shifts around the world. Our results indicate that the replacement of corals by macroalgae as the dominant benthic functional group is less common and less geographically extensive than assumed. Although we found evidence of moderate local increases in macroalgal cover, particularly in the Caribbean, only 4% of reefs were dominated by macroalgae (i.e., .50% cover). Across the Indo-Pacific, where regional averages of macroalgal cover were 9-12%, macroalgae only dominated 1% of the surveyed reefs. Between 1996 and 2006, phase shift severity decreased in the Caribbean, did not change in the Florida Keys and Indo-Pacific, and increased slightly on the Great Barrier Reef due to moderate coral loss. Coral reef ecosystems appear to be more resistant to macroalgal blooms than assumed, which has important implications for reef management.

Coral cover has declined on reefs worldwide with particularly acute losses in the Caribbean. Despite our awareness of the broad-scale patterns and timing of Caribbean coral loss, there is little published information on: (1) finer-scale, subregional patterns over the last 35 yr, (2) regional-scale trends since 2001, and (3) macroalgal cover changes. We analyzed the spatiotemporal trends of benthic coral reef communities in the Caribbean using quantitative data from 3777 coral cover surveys of 1962 reefs from 1971 to 2006 and 2247 macroalgal cover surveys of 875 reefs from 1977 to 2006. A subset of 376 reefs was surveyed more than once (monitored). The largest 1 yr decline in coral cover occurred from 1980 to 1981, corresponding with the beginning of the Caribbean-wide Acropora spp. white band disease outbreak. Our results suggest that, regionally, coral cover has been relatively stable since this event (i.e. from 1982 to 2006). The largest increase in macroalgal cover was in 1986, 3 yr after the regional die-off of the urchin grazer Diadema antillarum began. Subsequently, macroalgal cover declined in 1987 and has been stable since then. Regional mean (±1 SE) macroalgal cover from 2001 to 2005 was 15.3 ± 0.4% (n = 1821 surveys). Caribbeanwide mean (±1 SE) coral cover was 16.0 ± 0.4% (n = 1547) for this same time period. Both macroalgal and coral cover varied significantly among subregions from 2001 to 2005, with the lowest coral cover in the Florida Keys and the highest coral cover in the Gulf of Mexico. Spatio-temporal patterns from the subset of monitored reefs are concordant with the conclusions drawn from the entire database. Our results suggest that coral and macroalgal cover on Caribbean reef benthic communities has changed relatively little since the mid-1980s. KEY WORDS: Coral cover · Macroalgae · Coral disease · Coral bleachingResale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS Recent spatial patternsRecent (2001 to 2005) macroalgal cover varied significantly among subregions (ANOVA, p < 0.0001; Fig. 4) and ranged from 6.2 ± 4.0% (n = 16 surveys) in the Gulf of Mexico to 22.8 ± 1.6% (n = 100 surveys) in the south-

Students must learn content knowledge and develop scientific literacy skills to evaluate and use scientific information in real-world situations. Recognizing the accessibility of scientific information to the average citizen, we developed an instructional approach to help students learn how to judge the quality of claims. We describe a project-based applied learning (PAL) approach that utilizes engaging questions about biological issues relevant to students. Working through these projects, students are challenged to evaluate sources of information and communicate their understanding of scientific claims. We discuss challenges that students encounter and offer suggestions for enacting this approach in a general-education college classroom.

Many species create biogenic habitat that may vary in quality depending on its attributes. This variation may in turn affect species interactions among members of the attendant community. We describe a habitat-provisioning species that, with variation in a simple trait, produces dichotomous classes of habitat: one that serves as a predation refuge and the other that does not. Subtidal roots of the Caribbean red mangrove Rhizophora mangle are colonized by a diverse epibiont assemblage that includes many species of sponge. We experimentally demonstrated that roots touching the seafloor give benthic sea star predators access to their sponge prey living on the roots. After 6 wk, half of sponges on grounded roots were eaten, whereas sponges on suspended roots were uneaten. Correspondingly, in concomitant field surveys of mangrove root epibiont as semblages, we found very different sponge ensembles on the 2 root types. Even after standardizing for root area, suspended roots harbored 7 sponge species that covered an average of 91.3% of subtidal root length, while grounded roots, where sponges were exposed to sea star predation, had only 4 sponge species that covered 63.2% of root length. There was little overlap in species composition and a single sponge species Chondrilla caribensis, that was never eaten in our experiment, dominated grounded roots. This study suggests that a simple, dynamic trait of mangrove roots -groundedness -controls predator access, with consequences for assemblage composition.Resale or republication not permitted without written consent of the publisher

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