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Restoration of Stony Coral Tissue Loss Disease susceptible species with microfragmentation in Mexico

Updated: Dec 14, 2023

The Mesoamerican Reef (MAR) system is the second largest barrier reef in the world, extending approximately 1,000 km along the Caribbean coast of four countries: Mexico, Belize, Guatemala, and Honduras. The MAR is considered a biodiversity hotspot with high ecological, cultural, and economic value. However, the MAR’s coral reef communities are threatened by climate change, overfishing, pollution, and disease outbreaks.

Stony Coral Tissue Loss Disease (SCTLD) was first reported in the MAR in June of 2018, four years after being initially reported on reefs in southeast Florida. The disease affects approximately 22 reef-building coral species and has high prevalence and rates of transmission, often leading to extensive colony mortality (Fig. 1).

Figure 1. Stony coral susceptible species affected by Stony Coral Tissue Loss Disease (SCTLD).

The Arrecife de Puerto Morelos National Park (APMNP) is an MPA located at the northern extent of the MAR, in Quintana Roo, Mexico, a region of the Mexican Caribbean coast (Fig. 2). Encompassing approximately 90 km2 of coral reef, the APMNP contains an extended fringing reef with a well-developed backreef and a relatively flat forereef. Numerous disease outbreaks in the APMNP have also significantly reduced the numbers of essential reef-building coral species. By 2019, after SCTLD reached the APMNP, the disease was documented to have affected 43% of the APMNP susceptible species and by 2022, 55% of the surveyed colonies were diseased, resulting in major coral cover loss of massive, boulder species.

Figure 2. Drone footage of Puerto Morelos, Mexico. 
In response to the disease-related decline of massive stony corals in the APMNP, I created a balnaced experimental frameweork where I intruced coral tissue from SCTLD suceptilbe species using microfragmentation.Thus, the objective was to determine if by introducing tissue of SCTLD susceptible species exacerbates disease prevalence in natural colonies, to inform the APMNP if it’s the right time for active restoration to start. Additionally, since this is the first time that microfragmentation as a restoration tool is being used in the Mexican Caribbean, I looked into the fate of this microfragments at the outplant sites to provide a baseline of microfragmentation as a restoration tool within the APMNP.

To address these concerns, microfragmentation has been proposed as a restoration method. Stony coral microfragmentation, an asexual restoration technique that involves cutting coral colonies into ~4 cm microfragments, was proposed because it specifically targets massive coral species, which were most heavily impacted by the SCTLD outbreak.  Microfragmentation aims to propagate slow-growing, massive stony coral species to increase spatial distribution and maximize growth.

This study was conducted at the Arrecife de Puerto Morelos National Park, located in Puerto Morelos, Mexico. In September 2022, three species (Montastraea cavernosa, Orbicella annularis and O. faveolata) were cut into 1-4 cm2 microfragments (n = 1,504) and secured on plugs. Microfragments were kept at an ex situ nursery before being outplanted at six APMNP sites (Fig. 3). The selected sites were categorized by depth and reef morphology. I classified my sites into three depth categories which for the purposes of this study I denominated them as shallow (2 - 3 m) which encompass sites located in the reef crest, intermediate (5 - 6 m) with sites in the back reef, and deep in the fore reef (7 - 8 m).

To assess whether outplanting exacerbated SCTLD prevalence, six control sites with comparable depths and coral assemblages, were established approximately 100 m from the outplant sites. These control sites consisted of 20 by 20 m plots, each centered around a permanent pin, which was the same size as the outplant sites. Disease prevalence surveys were completed during each monitoring event to quantify disease prevalence in natural colonies at control and outplant sites.

Figure 3. Arrecife de Puerto Morelos National Park (APMNP) with the outplant and control sites (Inset: Mexico with APMNP highlighted in red box).

An equal distribution of bases representing all parent colonies, species, and base densities (3 and 7 plugs) were outplanted at six reef sites (Fig. 4). At each site, 50 bases were haphazardly distributed around a central pin (Fig. 5). Monitoring was carried out monthly for the first two months (December 2022 and January 2023) and then transitioned to a quarterly schedule, with monitoring occurring in May and August 2023. 

Figure 4. Cement bases used for outplanting with each containing 3 or 7 microfragments.
Figure 5. Schematic representation of outplant experimental design. A 20 m2 plot divided into four quadrants with 50 bases haphazardly distributed around a central pin.

Microfragment outplant success was assessed by survival, growth, and health conditions between species and site locations (Fig. 6). Additionally, during each monitoring event, SCTLD prevalence was recorded at outplant and control sites to evaluate if outplanting SCTLD-susceptible species affected disease prevalence in the natural population.

Figure 6. Camera and framer used to take base photographs. Examples of health conditions observed in the bases including predation, disease and bleaching. 

After 9-months, disease prevalence on natural colonies at control sites was 2.42% ± 0.64 SE while at outplant sites was 4.01% ± 0.55 SE, however even though it was higher at outpalnt sites, there was no significant increase in disease prevalence over time between the control and outplant sites due to the addtion of microfragment (p = 0.71; Fig. 7). Suggesting that restoration of SCTLD-suceptible spcies is not affecting the natural colonies in the APMNP.

Figure 7. SCTLD disease prevalence (%) over time in natural colonies at the outplant and control sites. 
Introducing SCTLD-susceptible stony coral species did not increase disease prevalence in the surrounding natural colonies at any sites, suggesting that additional restoration activities could be implemented in the APMNP.


Stay tunned for part 2!

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