Long-term change in coral community composition
Since the mid-20th century, shallow water reefs across
the Caribbean have transformed from systems dominated by competitive
corals to systems dominated by stress-tolerant and weedy corals (Figures
2, 3). At both the reef crest and midslope zones, coral community change
occurred via three stages: (1) significant declines in competitive
corals relative to the pre-human baseline occurring by the 1960s; (2)
significant increases in stress-tolerant and weedy corals occurring by
the 1970s and 1980s; and (3) significant declines or leveling-off of
stress-tolerant and weedy corals since the 1980s or 1990s (Table 2,
Figures 2, 3). These trends were consistent whether Millepora was
included or excluded from the competitive life history group and whetherOrbicella was included in the competitive or stress-tolerant
group, with the exception that the inclusion of both Orbicellaand Millepora in the competitive group rendered overall declines
in competitive corals non-significant at the reef crest zone (Figures
S1,S2, Table S5). For competitive corals in both zones and
stress-tolerant and weedy corals in the midslope zone, the first
significant change relative to the pre-human baseline occurred in the
Holocene, reflecting contrasting environmental conditions and/or data
types between the Pleistocene and Holocene (Figures 2,3).
The assessment of trends for individual species groups revealed that at
both reef zones, the prevalence of competitive Acropora palmataand A. cervicornis declined significantly between the Pleistocene
and Holocene periods. After the Holocene, the next significant decline
in competitive Acropora corals occurred in the 1960s; the
prevalence of these corals remained significantly lower than pre-human
levels from this point forward (Table 2, Figures 2a, 3a). In contrast,
prevalence of the competitive hydrozoan Millepora increased
significantly across the full time series, peaking in the late 1990s
(crest) or early 2000s (midslope). At the reef crest zone,Siderastrea was the only stress-tolerant taxon that increased
significantly from the pre-human period to present, while at the
midslope zone all stress-tolerant taxa except for Diploria andOrbicella increased significantly across the full time series
(Table 2, Figures 2b,3b). The post-1980s declines in the prevalence of
stress-tolerant corals that occurred at the reef crest zone were driven
by declines in Colpophyllia, Diploria, Montastrea
cavernosa , and Siderastrea while post-1990s leveling off in the
prevalence of this group at the midslope zone was driven by declining or
consistent prevalence of Colpophyllia, Diploria, andMontastrea cavernosa . At both reef zones, all weedy taxa
increased significantly across the full time series with the exception
of Madracis in the reef crest (Table 2, Figures 2c,3c). Initial
significant increases in individual weedy coral species primarily
occurred in the 1980s (crest) and in the 1970s (midslope). Significant
post-1980s declines in the weedy group at the reef crest reflect
contemporaneous declines in Agaricia , branching Porites ,
and P. astreoides , while significant post-1990s declines in the
weedy group at the midslope reflect declines in Agaricia and
branching Porites .