Dataset: 3 Species Coral Growth

Methodology: 

We conducted a manipulative experiment in the back reef lagoon of Mo′orea, French Polynesia (17°28′37″S 149°50′21″W) comparing monocultures of the corals A. hyacinthus, P. rus, and P. verrucosa to polycultures composed of all three species. We constructed 48 40 cm by 40 cm cement slabs affixed to the benthos and elevated on cinder blocks to prevent scour by sand or unconsolidated rubble; this elevation mimics the coral presence on raised bommies around our manipulation site. The upper surface of each slab contained a six by six grid space in which we embedded 18 upturned bottle caps per plot within every other space. Approximately eight-cm length branches of A. hyacinthus, P. rus, and P. verrucosa were fragmented from colonies in situ and epoxied individually into the cutoff neck of soda bottles, which were then attached to plots at randomized locations by screwing the bottle necks into the upturned caps within each plot (18 corals per plot, 864 corals in total). This produced n = 12 for each of the three monocultures and the polyculture, with treatments assigned to plots at random to assure interspersion of treatments. At the initiation of the experiment, corals and their epoxy/bottle-top base were wet-weighed in the field using an electronic scale (OHAUS Scout Pro) enclosed within a plastic container mounted to a tripod holding it above the water surface. This provided a wet mass starting value for each individual coral and its base.

Sampling and analytical procedures:

To assess coral growth, corals and their epoxy/bottle-top base were unscrewed from their treatment plot and wet-weighed in the field as described above. Twenty-four to 48 hours before this second weighing, each coral’s epoxy/bottle-top base was brushed clean of fouling organisms. Before all weighings, each coral was gently shaken 30 times to remove excess water, weighed, immediately placed back into the water, and reattached to its respective bottle cap. At the end of the experiment, each coral was separated from its epoxy/bottle-top base, and each coral and base were weighed separately to assess change in mass of the coral alone. Previously, we have used this method to determine, via subtraction, the coral mass and thus the percentage growth throughout the experimental period; however, in many cases, the epoxy/bottle tops used in this experiment did not exhibit clean breaks from their coral outplant. Thus, we decided to calculate the mean weight of all bottle tops and epoxy with visually clean breaks (326 of 864 bottle tops; mean = 21.76 g ± 0.08 g SE) and subtracted this value from each coral replicate to calculate percent coral mass change. 

We used permutation-based, linear mixed-effects (LME) models in the R package predictmeans to compare differences in the percentage mass change and tissue mortality of conspecific corals in monocultures versus polyculture, as well as the combined percentage mass change of all species in polycultures with that of all species in monocultures. In each analysis, plot type (monoculture or polyculture) was treated as a fixed factor, and individual replicate plots were treated as a random effect nested within plot type.