Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Initial mass and growth data, as change in mass over 33 days, for Acropora millepora corals exposed to one of nine experimental treatments of killer seaweeds. Experiments investigated how direct contact versus close proximity (approx. 1.5 cm) with macroalgae (Galaxaura rugosa, Sargassum polycystum) impacted the growth and other factors. 

These data are presented in Figure 1 of Clements et al, 2020. See 'Master ID Sheet.xlsx' in Supplemental Files for the treatment descriptions.

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. Following the acclimation period, corals were detached from the substratum and weighed in the field using an electronic scale (OHAUS Scout Pro) enclosed within a plastic container that was mounted to a tripod holding it above the water surface. Eighteen to 24 hrs before the weighing session, each coral’s bottle-top/epoxy base was brushed with a toothbrush to remove fouling organisms. Before weighing, each coral was gently shaken 30 times to remove excess water, and then weighed, immediately placed back into the water, and reattached to the substrate. 

Initial mass of coral branches did not differ among treatments (Linear mixed effect (LME) model, p = 0.328; mean mass ranged from 13.4–18.9 g).

Corals were 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 day 33, corals were detached from the substratum and reweighed in the field as previously described. Following the weighing session, corals were separated from their bottle/epoxy base and were weighed separately to determine changes in coral mass alone during the 33-day period (i.e. without the weight of the epoxy and bottle neck base).

Differences in relative growth (as a percentage of initial weight) among treatments were analyzed using LME models in the R package nlme [Pinheiro et al, 2017], with coral colony used as a random factor in all analyses. When necessary, the varIdent argument was used to control for heteroscedasticity. Subsequent pairwise comparisons were performed using the generalized linear hypothesis test (glht) in the R package multcomp [Hothorn et al, 2008].

BCO-DMO Processing Notes:
- data submitted in Excel file "Coral Growth Data.xlsx" sheet "Mass Change" extracted to csv
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions

Extracted from the NSF award abstract:

Coral reefs are in dramatic global decline, with reefs commonly converting from species-rich and topographically-complex communities dominated by corals to species- poor and topographically-simplified communities dominated by seaweeds. These phase-shifts result in fundamental loss of ecosystem function. Despite debate about whether coral-to-algal transitions are commonly a primary cause, or simply a consequence, of coral mortality, rigorous field investigation of seaweed-coral competition has received limited attention. There is limited information on how the outcome of seaweed-coral competition varies among species or the relative importance of different competitive mechanisms in facilitating seaweed dominance. In an effort to address this topic, the PI will conduct field experiments in the tropical South Pacific (Fiji) to determine the effects of seaweeds on corals when in direct contact, which seaweeds are most damaging to corals, the role allelopathic lipids that are transferred via contact in producing these effects, the identity and surface concentrations of these metabolites, and the dynamic nature of seaweed metabolite production and coral response following contact. The herbivorous fishes most responsible for controlling allelopathic seaweeds will be identified, the roles of seaweed metabolites in allelopathy vs herbivore deterrence will be studied, and the potential for better managing and conserving critical reef herbivores so as to slow or reverse conversion of coral reef to seaweed meadows will be examined.

Preliminary results indicate that seaweeds may commonly damage corals via lipid- soluble allelochemicals. Such chemically-mediated interactions could kill or damage adult corals and produce the suppression of coral fecundity and recruitment noted by previous investigators and could precipitate positive feedback mechanisms making reef recovery increasingly unlikely as seaweed abundance increases. Chemically-mediated seaweed-coral competition may play a critical role in the degradation of present-day coral reefs. Increasing information on which seaweeds are most aggressive to corals and which herbivores best limit these seaweeds may prove useful in better managing reefs to facilitate resilience and possible recovery despite threats of global-scale stresses. Fiji is well positioned to rapidly use findings from this project for better management of reef resources because it has already erected >260 MPAs, Fijian villagers have already bought-in to the value of MPAs, and the Fiji Locally-Managed Marine Area (FLMMA) Network is well organized to get information to villagers in a culturally sensitive and useful manner.

The broader impacts of this project are far reaching. The project provides training opportunities for 2-2.5 Ph.D students and 1 undergraduate student each year in the interdisciplinary areas of marine ecology, marine conservation, and marine chemical ecology. Findings from this project will be immediately integrated into classes at Ga Tech and made available throughout Fiji via a foundation and web site that have already set-up to support marine conservation efforts in Fiji and marine education efforts both within Fiji and internationally. Business and community leaders from Atlanta (via Rotary International Service efforts) have been recruited to help organize and fund community service and outreach projects in Fiji -- several of which are likely to involve marine conservation and education based in part on these efforts there. Media outlets (National Geographic, NPR, Animal Planet, Audubon Magazine, etc.) and local Rotary clubs will be used to better disseminate these discoveries to the public.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

Rasher DB, Stout EP, Engel S, Kubanek J, and ME Hay. "Macroalgal terpenes function as allelopathic agents against reef corals", Proceedings of the National Academy of Sciences, v. 108, 2011, p. 17726.

Beattie AJ, ME Hay, B Magnusson, R de Nys, J Smeathers, JFV Vincent. "Ecology and bioprospecting," Austral Ecology, v.36, 2011, p. 341.

Rasher DB and ME Hay. "Seaweed allelopathy degrades the resilience and function of coral reefs," Communicative and Integrative Biology, v.3, 2010.

Hay ME, Rasher DB. "Corals in crisis," The Scientist, v.24, 2010, p. 42.

Hay ME and DB Rasher. "Coral reefs in crisis: reversing the biotic death spiral," Faculty 1000 Biology Reports 2010, v.2, 2010.

Rasher DB and ME Hay. "Chemically rich seaweeds poison corals when not controlled by herbivores", Proceedings of the National Academy of Sciences, v.107, 2010, p. 9683.