DOI: 10.25903/ce1s-yf78
title: Data from: Sea-weeding enhances early coral survival on seeding devices, but benefits of seeding diminish after one year

description: <p><b>Background [Extract from Related publication]: </b>Borrowing from principles of aerial seeding in terrestrial reforestation, coral seeding utilises seeding “devices” designed to increase coral spat survival. However, device-assisted coral survival has not been compared to natural survivorship, nor have devices been trialled in environments with strong competitors such as macroalgae. Herein, we deployed seeded devices alongside terracotta tiles, a proxy for natural coral recruitment dynamics. Tiles and devices were deployed to plots examining ongoing macroalgae removal (“sea-weeding”), and survival was monitored over two years. First-year coral survival was enhanced on devices compared to natural survival, and devices conferred the greatest survival benefit when deployed in areas where “sea-weeding” was undertaken. However, over the second year, the benefits of sea-weeding for device-assisted survival were lost, with no significant difference in survival on devices in control versus weeded plots. On average, devices retained 1.3 surviving colonies at two years, which was lower than naturally-occurring juvenile density in removal plots, but higher than control plots. Several factors influenced survival, including the starting spat density, orientation of deployment surface, and site. After two years, 50% of devices yielded one live coral, but site-based survival varied between 37% and 93%. The estimated cost per surviving coral varied when accounting for site-based survival (high survival, $334 coral-1; low survival $577 coral-1), which could be reduced via future efficiencies. The results of this study inform the potential outcomes of coral seeding on macroalgae dominated reefs, and highlight that assessing survival up to one year is not sufficient to measure long-term restoration goals.</p>

<p><b>Methods [Partially Extracted from publication]:</b> This study builds upon a long-term project investigating the impacts of macroalgae removal on the fringing coral reefs of Yunbenun (Magnetic Island), on the central inshore region of Australia’s Great Barrier Reef, and described previously in Smith et al. (2023, 2022). Twelve 5 m x 5 m plots were established in each of two bays (Florence Bay, Arthur Bay) on the inshore fringing reefs of Yunbenun (total n = 24 plots). Half of these (n = 6 plots per bay) were randomly assigned as “control” plots, while the other half were assigned as “removal,” where all fleshy macroalgae were removed by hand. Macroalgae were removed in October 2021, July and October 2022, May and July 2023. Site characteristics are described in Smith et al. (2023). </p>

<p>At multiple time points through the experiment, in situ surveys were conducted to quantify macroalgae density and height as previously described (Smith, Brown, et al. 2022). Briefly, within each 25 m2 plot, Sargassum holdfast density and height  were used to estimate biomass in each plot using the formula (Hoey 2010): Wet weight [g m-2] = 0.5637 [g cm-1] x height [cm] X density [num m-2]. Coral seeding devices were populated with “plugs” seeded with live juveniles of <i>Acropora kenti</i>; devices were labelled with unique numbers to allow tracking of individual plugs through time. Devices were designed with protrusions intended to provide coral spat refuge from grazing/predation by herbivorous fishes (see Whitman et al. 2024 for full device design details). Three plugs (one with juveniles from each 500 L culture tank) were placed in the upward-facing (“top”) position, and three in a side-facing (“side”) position. Plugs with the highest number of individual spat were selected visually. All plugs were photographed in their device using a Nikon D810 camera prior to deployment. The number of individuals per plug was counted from photographs using the manual class counting function in the microscopy software Capture (version 2.2). All individuals were counted and classified as aggregates or singletons, and if aggregates, the number of polyps were counted. Aggregates were defined as two or more polyps with shared tissue between them.</p>

<p>On 24 November 2021, seeded devices were transported to the field by boat in 100 L containers filled with seawater. Within each of the twelve 25 m2 experimental plots per bay, five devices were haphazardly installed onto stainless steel threaded rod hammered into the benthos (total n = 60 devices per bay; under GBRMPA permit G21/45348.1). Following deployment, the devices were censused approximately every three months for 21 months. Censusing was completed visually by a SCUBA diver, whereby each device was unscrewed from its rod, each plug closely examined for live corals, and scored 1 for presence of any live, and 0 for no live <i>A.  kenti</i> coral.</p>

<p>At the final census (20 August 2023), devices were removed from experimental plots and transported to SeaSim in 100 L containers filled with seawater. Each device was photographed and closely inspected to count individual survivors. Individuals were identified as colonies that were homogenous in appearance and had a visible boundary between other colonies and/or an allogenic response could be visualised where boundaries were shared. Each individual was measured (maximum length, perpendicular width, height) in mm using digital callipers.</p>

</p>To compare device-assisted coral survival to natural survival, we also deployed 11 cm X 11 cm X 1 cm terracotta tiles to the experimental field plots (n = 10 haphazardly placed tiles per plot, total 240 tiles). Tiles were deployed between 24 – 27 August 2021, and installed the same way as seeded devices (i.e., screwed onto a threaded stainless-steel rod hammered into the benthos). Tiles were labelled with unique numbers to enable tracking of individual tiles and retrieved for censusing three times within the first year of device deployment, at similar times as devices censuses. At each census, the tiles were unscrewed from their rods, transported to land in 100 L bins of seawater, all live corals counted and photographed under a Nikon SMZ745 photomicroscope, then tiles were returned to their original position within each plot. All tiles were returned to their field locations within 24 hrs of being collected, and while on land were maintained at a constant temperature, with aeration from battery operated aquarium pumps. The final census occurred and tiles were removed on 13 September 2022.</p>

</p>We also conducted in situ surveys to compare end-point survival on devices to juvenile densities on natural substrata in October 2023. Within each of the twenty-four 25m2 experimental field plots, the number of juvenile corals ≤4 cm diameter was counted within each of three, haphazardly thrown replicate 1m x 1m quadrats.</p>

<p><b>This data record contains:</b><p>
<ul>
<li>one .csv files containing in situ survey data for juvenile presence/absence on devices</li>
<li>one .csv file containing census retrieval information</li>
<li>one .csv file containing removed macroalgae biomass data</li>
<li>one .csv file containing endpoint sizes of seeded corals</li>
<li>two .csv files containing macroalgae density and canopy height data</li>
<li>one .csv file containing in situ, naturally occurring coral recruit data</li>
<li>one .csv file containing the count of corals seeded per plug</li>
<li>one .csv file containing the count of corals on settlement tiles </li>
<li>one .R file containing analytical script of all data</li>
</p>