Dataset: Coral Photosynthetic Efficiency

Methodology:

To create standardized units of coral, nine ~6-8 cm length branches of Acropora millepora were collected from twelve separate colonies (108 branches total) within Votua’s MPA during October 2014 and individually epoxied (Emerkit) into the cut-off necks of inverted plastic bottles. These were then anchored on the reef by screwing them individually into an upturned bottle cap embedded within the substrate (see Video S1 at http://www.int-res.com/articles/suppl/m586p011_supp/ for an example of this experimental method) and allowed to acclimate for ~1 month. Corals were then subjected to one of nine experimental treatments for 33 days: (1) direct contact with four thalli of Galaxaura rugosa (live seaweed), (2) close proximity (i.e. ~1.5cm away, no contact) to four thalli of Galaxaura, (3) direct contact with four Galaxaura mimics (microfiber dust cloth), (4) close proximity to four Galaxaura mimics, (5) direct contact with four Sargassum polycystum thalli (live seaweed), (6) close proximity to four Sargassum thalli, (7) direct contact with four Sargassum mimics (plastic aquarium plants), (8) close proximity to four Sargassum mimics, or (9) no seaweed or mimic exposure (control) (n = 9-13 per treatment).  

Sampling and analytical procedures:

At 32 days, we used PAM fluorometry (Diving-PAM, Walz, Germany) to assess treatment effects on coral photosynthetic efficiency via measurements of photosystem II (PSII) quantum yield of zooxanthellae within each coral (i.e. effective quantum yield, ՓPSII). All readings were taken in situ on light-adapted corals between 0900-1400 h and were interspersed among treatments through time to prevent confounding treatment effects with time or changing light conditons. We took three readings haphazardly around each coral branch; these were averaged to obtain an “overall” photosynthetic efficiency value for each coral. We also measured a  “worst-case” photosynthetic efficiency reading taken at the location that visually appeared most damaged on each coral. For each measure of photosynthetic efficiency, we separately compared ՓPSII values of control corals to those of corals in direct contact or close proximity with Galaxaura or its mimics or Sargassum or its mimics using linear mixed effect (LME) models in R (v. 3.6.1) (R Core Team 2016) with the package nlme (Pinheiro et al. 2017). Coral colony was used as a random factor in all analyses. Subsequent pairwise comparisons were performed using Tukey contrasts with the generalized linear hypothesis test (glht) in the R package multcomp (Hothorn et al. 2008).