Dataset: Octocoral abundance by genera

Based on Tsounis and Edmunds (In press), Ecosphere: 

Community structure was characterized for four assemblage constructs that employed annual means for dependent variables (cover or abundance). First, the scleractinian-focused assemblage was quantified using the percentage cover of scleractinians (pooled among taxa), macroalgae, and CTB. Second, the octocoral-focused assemblage was quantified using octocoral abundance (pooled among taxa) together with cover of macroalgae, and CTB. Third, the octocoral genus assemblage focused on octocoral abundance resolved to genus, or unknowns. Fourth, a complete assemblage was used, containing scleractinians (all taxa), octocorals (abundance by genus), macroalgae and CTB. Data for each benthic group were presented untransformed as means +/- SE by year on scatterplots.

All analyses of scleractinian-focused, octocoral-focused, octocoral genera, and complete assemblages were based on resemblance matrices using Bray-Curtis similarities. Data for the scleractinian-focused assemblage consisted of percent cover and were square root transformed; data for the octocoral-focused and complete assemblage consisted of both percent cover and numerical abundance, and therefore were z-score standardized (Sokal and Rohlf 2012); and data for the octocoral genera were z-score standardized to optimize the performance of PCoA for the zero-inflated data. A dummy value of 3 was added to z-score standardized data to create positive values that could analyzed in this statistical framework.

Non-metric multidimensional scaling (nMDS) was used to visualize multivariate trends in community structure for the four assemblages. To prepare nMDS plots, multiple restarts of 999 iterations were used until stress stabilized and ordinations were repeatable (after Clarke and Warwick 2001). In these plots, years were represented as circles scaled to scleractinian cover in the scleractinian-focused analysis, and to pooled abundance of octocorals in the octocoral focused and octocoral genera analyses. Sampling years were clustered using the SIMPROF routine in PRIMER-E, with 999 permutations and significant clusters identified at an alpha of 0.05. SIMPROF results were displayed as similarity contours on the respective nMDS plots visualizing hierarchical similarity among years (after Clarke and Warwick 2001). To evaluate similarities between two groupings of years that became apparent during initial analysis (as in Edmunds 2013; Edmunds and Lasker 2016), we used an iterative procedure for each graph to determine the highest value of dissimilarity percentage that would describe the groups of years separated in nMDS state space. To identify the contribution of each benthic group to inter-annual variability, a principal coordinate analysis (PCoA) was performed using the cmdscale function in the R statistical package (R Development Core Team 2008). Loading scores were calculated as the Pearson correlations of each dependent variable (i.e., benthic group) against PCO1 and PCO2, and were displayed when significant (P less than 0.05) as vectors scaled to a maximum length of 1. The PCoA were based on Bray-Curtis similarities that were produced using the vegan package for R (Oksanen et al. 2015).

Question 1. To test whether the description of community dynamics differ when described with the four assemblages constructs, we used a multivariate correlation procedure with significance determined within a permutational framework using a Mantel test (Legendre and Legendre 1998). First we compared the scleractinian-focused assemblage with the octocoral-focused assemblage; second, we compared the scleractinian-focused assemblage with the octocoral genera assemblage; and third, we tested whether the scleractinian-focused assemblage differed from the complete assemblage. The Mantel test was performed using the Vegan package in R [Oksanen et al. 2015; R Development Core Team 2008]).

Each of the four assemblages was tested for associations with all combinations of the four measures of physical conditions, using Spearman rank correlation (Clarke and Ainsworth 1993). The Bioenv function (Clarke and Ainsworth 1993) was used for correlations, and was followed with a Mantel procedure (Legendre and Legendre 1998) to identify the set of physical variables most strongly associated with the biological variables, with significance evaluated in a permutational framework. The Bioenv function was performed using the vegan package for R (R Development Core Team 2008 [Oksanen et al. 2015]).

Analysis of general implications

To address general implications of our findings, the Yawzi Point versus Tektite contrast was interpreted as a comparison of a reef dominated by living Orbicella annularis (i.e., Tektite), with one dominated by antecedent (but dead) colonies of O. annularis with the decline in cover of this species having taken place since 1987. In this format, the contrast has utility in evaluating how the regional trend for declining cover of O. annularis (e.g., Hughes and Tanner 2000, Edmunds 2015) is likely to influence the community dynamics of octocorals. Central to this interpretation was an inferential test of octocoral community dynamics at Yawzi Point versus Tektite, and this was accomplished using the Mantel test to compare all four assemblages as described above.

BCO-DMO Processing Notes:

-Reformatted column names to comply with BCO-DMO standards.
-Replaced "no data" with "nd"
-Changed significant figures to reflect the accuracy of the measuring system.