Community dissimilarity
Within-country community dissimilarity declined significantly from the historic period to present at both reef zones; the decline was more striking in the latter (Fig 4). Because the Pleistocene and Holocene communities at both reef zones were more variable and had notably lower average dissimilarity values compared to subsequent periods—likely due to time averaging of the fossil data which comprise these time bins—we designated the historical time bin (1500-1959) as the baseline for this community metric. At both the reef crest and midslope zones, pairwise comparisons of mean within-country dissimilarity values showed significant declines from the baseline historical period (1500-1959) to most recent period (2005-2011), with the first significant decline relative to the baseline occurring in 2000-2004 at the reef crest and in 1985-1989 at the midslope zones (Figure 4).