Table of Contents

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

Replicate: Replicate number (1 to 80) is the unique identification for each individual margin of PAC that was tagged between August 2019 and January 2020 in order to measure the growth rate of PAC.

Site:  The two sites within Lameshur Bay, St. John, USVI where margins of PAC were tagged to determine growth rate of PAC, and whether it varied between sites (Cabritte Horn, Tektite).

Depth: Depth in meters (either 3 or 9 m) at the site where tags were used to determine growth rate of PAC, and whether it varied between depths (3 meters depth vs 9 meters depth)

Growth Rate:  Growth rate of PAC margin (micrometer/day) calculated using the number of days between when the tag was initially deployed to mark the margin of PAC to when the margin was re-measured again in January 2020.

Related datasets for Williams and Edmunds (2021) Coral Reefs manuscript:
Figure 2a, https://www.bco-dmo.org/dataset/836071
Figure 3, https://www.bco-dmo.org/dataset/836164
Tables 1 and 2, https://www.bco-dmo.org/dataset/836304

Overview
        This study took place on the south shore of St. John, and surveys were completed in August 2019 and January 2020 at Cabritte Horn and Tektite on the eastern side of Great Lameshur Bay. These sites were selected because the abundance of Peyssonnelid Algal Crusts (PAC) has been measured in these locations since 2015, and the high abundance of PAC created a tractable system to test for the outcomes of PAC-coral interactions. The coral community structure in St. John from 1987-present is described elsewhere, but in brief, coral cover has been < 4.5% at six sites since 1992, but at two other sites, it has declined from 45% to 4% (Yawzi Point) and 32% to 27% (Tektite) from 1987–2019. Over the same period, the cover of macroalgae has increased, and the rest of the hard substratum has remained covered by crustose coralline algae, turf algae, and bare rock (combined as “CTB”). The high abundance of igneous rock on these reefs provides substratum suitable for growth of PAC. As PAC in St. John is more abundant in shallow (3–5 m) versus deep (5–9 m) water, surveys were designed to contrast PAC between depths. Sampling along a 15 m transect at each site and depth was used to evaluate PAC abundance, growth, and competitive encounters. 

Growth of PAC
Linear growth of PAC on natural substrata
        Along the same transects used to quantify PAC cover, tags (n = 20 tags per site) were placed next to corals that were interacting with PAC, and they were used to measure both the growth rate of PAC and the outcome of the interactions with corals (described in dataset 836304). Corals for tagging were selected haphazardly as encountered along the transect line, and in each case, the margin of PAC engaged in the coral-PAC encounter was marked with a numbered aluminum tag (32-mm diameter) epoxied (Z-Spar Splash Zone A-788) to non-living substratum adjacent to the interaction. When the tags were deployed in August 2019, the shortest distance between the tag and the margin of the PAC was measured (± 0.1 mm) using calipers. In January 2020, the tags were located using a metal detector (Vibra-Probe 580, Treasure Products, Inc.), and for each coral, the tag was used as a fixed reference towards which the linear growth of PAC was recorded. The distance between the tag and PAC was measured again, and the growth of PAC recorded as the change in distance between the PAC and tag was expressed as µm d-1. This method resolved the capacity of PAC to spread over rock, but it did not explicitly evaluate growth towards the coral.

Statistical analyses
Differences in linear growth rate of PAC on natural substrata were analyzed using a two-way fixed effects ANOVA, with site and depth as fixed factors. As testing for an effect of depth was a primary objective of this study, growth rates were compared between depths using planned comparisons. 

Assuming that the coral-PAC interactions encountered along the transect lines effectively were randomly selected, their frequency of occurrence in August 2019 was tested for independence among depths (3 m vs 9 m), sites (Tektite vs Cabritte Horn), and interaction type (described above) using log-linear analysis. This was used to determine whether the frequency of each interaction type could be compared between times (August 2019 vs January 2020) with a model simplified by pooling among depths and sites, with the rationale that these effects were not significant.

Statistical analyses were completed using the open-source software R ver. 3.5.1, with lme4 and Matrix packages for log-linear analysis, and DescTools for the G-test. Statistical assumptions of ANOVA were tested using graphical analysis of the residuals.

BCO-DMO Processing:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- added Latitude and Longitude columns
- units removed from field names and added to Parameter Description metadata section
 

Describing how ecosystems like coral reefs are changing is at the forefront of efforts to evaluate the biological consequences of global climate change and ocean acidification. Coral reefs have become the poster child of these efforts. Amid concern that they could become ecologically extinct within a century, describing what has been lost, what is left, and what is at risk, is of paramount importance. This project exploits an unrivalled legacy of information beginning in 1987 to evaluate the form in which reefs will persist, and the extent to which they will be able to resist further onslaughts of environmental challenges. This long-term project continues a 27-year study of Caribbean coral reefs. The diverse data collected will allow the investigators to determine the roles of local and global disturbances in reef degradation. The data will also reveal the structure and function of reefs in a future with more human disturbances, when corals may no longer dominate tropical reefs.

The broad societal impacts of this project include advancing understanding of an ecosystem that has long been held emblematic of the beauty, diversity, and delicacy of the biological world. Proposed research will expose new generations of undergraduate and graduate students to natural history and the quantitative assessment of the ways in which our planet is changing. This training will lead to a more profound understanding of contemporary ecology at the same time that it promotes excellence in STEM careers and supports technology infrastructure in the United States. Partnerships will be established between universities and high schools to bring university faculty and students in contact with k-12 educators and their students, allow teachers to carry out research in inspiring coral reef locations, and motivate children to pursue STEM careers. Open access to decades of legacy data will stimulate further research and teaching.

NSF Award Abstract:
Coral reefs are exposed to a diversity of natural and anthropogenic disturbances, and the consequences for ecosystem degradation have been widely publicized. However, the reported changes have been biased towards fishes and stony corals, and for Caribbean reefs, the most notable example of this bias are octocorals ("soft corals"). Although they are abundant and dominate many Caribbean reefs, they are rarely included in studies due to the difficulty of both identifying them and in quantifying their abundances. In some places there is compelling evidence that soft corals have increased in abundance, even while stony corals have become less common. This suggests that soft corals are more resilient than stony corals to the wide diversity of disturbances that have been impacting coral corals. The best coral reefs on which to study these changes are those that have been studied for decades and can provide a decadal context to more recent events, and in this regard the reefs of St. John, US Virgin Islands are unique. Stony corals on the reefs have been studied since 1987, and the soft corals from 2014. This provides unrivalled platform to evaluate patterns of octocoral abundance and recruitment; identify the patterns of change that are occurring on these reefs, and identify the processes responsible for the resilience of octocoral populations. The project will extend soft coral monitoring from 4 years to 8 years, and within this framework will examine the roles of baby corals, and their response to seafloor roughness, seawater flow, and seaweed, in determining the success of soft corals. The work will also assess whether the destructive effects of Hurricanes Irma and Maria have modified the pattern of change. In concert with these efforts the project will be closely integrated with local high schools at which the investigators will host marine biology clubs and provide independent study opportunities for their students and teachers. Unique training opportunities will be provided to undergraduate and graduate students, as well as a postdoctoral researcher, all of whom will study and work in St. John, and the investigators will train coral reef researchers to identify the species of soft corals through a hands-on workshop to be conducted in the Florida Keys.

Understanding how changing environmental conditions will affect the community structure of major biomes is the ecological objective defining the 21st century. The holistic effects of these conditions on coral reefs will be studied on shallow reefs within the Virgin Islands National Park in St. John, US Virgin Islands, which is the site of one of the longest-running, long-term studies of coral reef community dynamics in the region. With NSF-LTREB support, the investigators have been studying long-term changes in stony coral communities in this location since 1987, and in 2014 NSF-OCE support was used to build an octocoral "overlay" to this decadal perspective. The present project extends from this unique history, which has been punctuated by the effects of Hurricanes Irma and Maria, to place octocoral synecology in a decadal context, and the investigators exploit a rich suite of legacy data to better understand the present and immediate future of Caribbean coral reefs. This four-year project will advance on two concurrent fronts: first, to extend time-series analyses of octocoral communities from four to eight years to characterize the pattern and pace of change in community structure, and second, to conduct a program of hypothesis-driven experiments focused on octocoral settlement that will uncover the mechanisms allowing octocorals to more effectively colonize substrata than scleractinian corals on present day reefs. Specifically, the investigators will conduct mensurative and manipulative experiments addressing four hypotheses focusing on the roles of: (1) habitat complexity in distinguishing between octocoral and scleractinian recruitment niches, (2) the recruitment niche in mediating post-settlement success, (3) competition in algal turf and macroalgae in determining the success of octocoral and scleractian recruits, and (4) role of octocoral canopies in modulating the flux of particles and larvae to the seafloor beneath. The results of this study will be integrated to evaluate the factors driving higher ecological resilience of octocorals versus scleractinians on present-day Caribbean reefs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.