Planulae densities in <i>P</i>. <i>astreoides</i> tissues.

<p>Shallow, mid-depth, and mesophotic planulae densities each week. Upper and lower hinges correspond to the first and third quartiles, bars correspond to medians and whiskers extend to the highest and lowest values within 1.5 times the inter-quartile range. Outliers are represented as dots. Lines connect mean values, and are included to illustrate increasing planulae density, and the loss of those planulae from tissues, presumably due to planulation. At only one week (week 4) were planulae densities found to be significantly different between sites, with higher densities in mesophotic colonies (one-way ANOVA/Tukey’s-HSD, p = 0.009).</p

Differences in attributes of passive particles released at spawning versus control sites for 1 – 10 days post release.

<p>A) index of particle aggregation. B) average distance of particles from release site (km). C) percentage of particles retained within 20 km of release site. D) average distance of particles from shore (km). *p<0.05, **p<0.01, ***p<0.001.</p

Snapshot of Gladden Spit model output showing important physical features and processes of eddy formation.

<p>Pink dotted lines are added for ease of visualizing behavior at eddy edge vs. eddy centers. Cape (not shown) is to the left of the extent. A) Isopycnals (density anomalies in km m⁻³) plotted in an alongshore cross section at y = 20 (black dashed line in B). B) Plot of potential vorticity values (in m⁻¹ s⁻¹) in the surface layer to view the presence of eddies. Red indicates positive vorticity; blue indicates negative vorticity. C) Contours of isopycnals; concentrated lines denote frontal zones. D) Plot of absolute vertical velocities (m s⁻¹) * density anomalies (kg m⁻³) in the surface layer. Red indicates vertical movements.</p

Left: Bathymetry in the Mesoamerican Barrier Reef region with study sites indicated.

<p>Upper right: View of Control #2 site from N to S. Lower right: View of Rocky Point site from N to S.</p

Depth-Independent Reproduction in the Reef Coral <i>Porites astreoides</i> from Shallow to Mesophotic Zones

<div><p>Mesophotic coral ecosystems between 30–150 m may be important refugia habitat for coral reefs and associated benthic communities from climate change and coastal development. However, reduced light at mesophotic depths may present an energetic challenge to the successful reproduction of light-dependent coral organisms, and limit this refugia potential. Here, the relationship of depth and fecundity was investigated in a brooding depth-generalist scleractinian coral, <i>Porites astreoides</i> from 5–37 m in the U.S. Virgin Islands (USVI) using paraffin tissue histology. Despite a trend of increasing planulae production with depth, no significant differences were found in mean peak planulae density between shallow, mid-depth and mesophotic sites. Differential planulae production over depth is thus controlled by <i>P</i>. <i>astreoides</i> coral cover, which peaks at 10 m and ~35 m in the USVI. These results suggest that mesophotic ecosystems are reproductive refuge for <i>P</i>. <i>astreoides</i> in the USVI, and may behave as refugia for <i>P</i>. <i>astreoides</i> metapopulations providing that vertical larval exchanges are viable.</p></div

Velocity and density profiles used as initial conditions for the model.

<p>Dotted lines: profiles from HYCOM for individual days during the spawning period. Solid line: idealized profile used in the model.</p

Selected views of reproductive structures of <i>P</i>. <i>astreoides</i>.

<p>(a) Cross-sectional view showing the simultaneous presence of oocytes, spermaries and planulae larvae. The actinopharynx of two polyps is also shown for reference. (b) A close-up view of (a), showing internal details of a larva, including mesenteries. (c) Longitudinal view showing the simultaneous presence of larvae and oocytes. (d) A close-up longitudinal view, showing a larva extruded from the oral opening of a polyp. (e) A longitudinal view of a single polyp, showing the actinopharynx and stage IV ova. (f) A 40x magnification of a stage V spermary and stage IV oocyte. Spermatozoa are arranged in spermatids within the spermary. (o = oocyte/ovum; s = spermary; p = planulae larva; act = actinopharynx; m = mesenteries; bar = 500 μm [a-d], 200 μm [e], and 50 μm [f]).</p

Snapshots of potential vorticity (in m⁻¹ s⁻¹) of surface layer for (A) Gladden Spit and (B) Control #3.

<p>Snapshots of potential vorticity (in m⁻¹ s⁻¹) of surface layer for (A) Gladden Spit and (B) Control #3.</p

Predictions of planulae production over depth.

<p>(a) Relationship of depth and cover of <i>P</i>. <i>astreoides</i> at sites south of St. Thomas, USVI derived from the Territorial Coral Reef Monitoring Program [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146068#pone.0146068.ref030" target="_blank">30</a>] from 2001–2012. (b) Predicted number of larvae produced in a hypothetical 1 km² coral reef over depth, calculated as the products of planulae per cm² and coral cover.</p

Frequency of <i>P</i>. <i>astreoides</i> reproductive products found in histological analyses.

<p>Values plotted represent the percent of total colonies (3 sites, 5 sampling days, n ≈ 5, N = 76) containing (a) oocytes/ova, (b) spermaries and (c) planulae on each sampling day at each site. The lunar cycle is shown below the x-axis.</p