Introduction
Living cover of reef-building corals has declined on Caribbean reefs by
50 to 80 percent since systematic monitoring began in the late 1970s
[1,2] with many reefs transformed from coral- to algal-dominated
habitats [2,3]. Coral declines have been attributed to multiple
anthropogenic stressors including fishing, land-based pollution, and
global warming as well as epizootics afflicting corals and urchins
[2-4]. The mass mortality of the long-spined sea urchinDiadema antillarum in the early 1980s removed the last abundant
herbivore from reefs that were largely devoid of herbivorous fish after
decades to centuries of overfishing [5-8], precipitating an
explosion of macroalgae on reefs across the Caribbean [2]. Outbreaks
of “White Band Disease” appeared on many reefs around this same time,
eventually killing over 80% of elkhorn coral Acropora palmatawhich previously dominated reef crest zones and staghorn coralAcropora cervicornis which previously dominated midslope zones
[9-11]. These events were followed by regional coral bleaching in
the 1990s, leading to further increases in coral diseases and in some
instances a further replacement of corals by macroalgae [12]. These
factors acted synergistically to rapidly transform coral communities. A
recent Caribbean-wide analysis of Acropora presence and dominance
from the pre-human period to the present revealed that the loss of these
corals initially began in the 1950s and 1960s, decades before the first
recorded observations of coral disease and bleaching [13].
While the long-term decline of Caribbean acroporid corals has been
documented on a regional scale [13], the effects of Acroporaloss on Caribbean reef coral community composition and ecosystem
functioning are unknown. Although isolated surveys of altered reefs have
found an increase in the relative abundance of low-relief “weedy”
species such as Porites and Agaricia over the past few
decades [14-17], the magnitude and geographic extent of community
change are unresolved. Assessing
long-term change in the full reef-building coral community will shed
light on the ecological causes and consequences of recent coral declines
and assist in guiding appropriate management interventions. We compiled
an extensive dataset on the prevalence of common hermatypic coral
species and genera at thousands of individual reef sites across the
Caribbean spanning the Late Pleistocene epoch (~131,000
ybp)—when humans were absent from the Americas—up to 2011. By
pinpointing the initial timing of major community transformations, we
inferred general anthropogenic causes of change (i.e., local human
stressors and/or climate change). To provide additional insight into the
ecological context of change, we also tracked change in (a) major coral
ecological guilds based on various life history traits and (b)
inter-site community heterogeneity.