Potential Connectivity of Coldwater Black Coral Communities in the Northern Gulf of Mexico

<div><p>The black coral <i>Leiopathes glaberrima</i> is a foundation species of deep-sea benthic communities but little is known of the longevity of its larvae and the timing of spawning because it inhabits environments deeper than 50 m that are logistically challenging to observe. Here, the potential connectivity of <i>L</i>. <i>glaberrima</i> in the northern Gulf of Mexico was investigated using a genetic and a physical dispersal model. The genetic analysis focused on data collected at four sites distributed to the east and west of Mississippi Canyon, provided information integrated over many (~10,000) generations and revealed low but detectable realized connectivity. The physical dispersal model simulated the circulation in the northern Gulf at a 1km horizontal resolution with transport-tracking capabilities; virtual larvae were deployed 12 times over the course of 3 years and followed over intervals of 40 days. Connectivity between sites to the east and west of the canyon was hampered by the complex bathymetry, by differences in mean circulation to the east and west of the Mississippi Canyon, and by flow instabilities at scales of a few kilometers. Further, the interannual variability of the flow field surpassed seasonal changes. Together, these results suggest that a) dispersal among sites is limited, b) any recovery in the event of a large perturbation will depend on local larvae produced by surviving individuals, and c) a competency period longer than a month is required for the simulated potential connectivity to match the connectivity from multi-locus genetic data under the hypothesis that connectivity has not changed significantly over the past 10,000 generations.</p></div

Connectivity diagrams VK906 and GB140.

<p>As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156257#pone.0156257.g008" target="_blank">Fig 8</a> but for larvae released at VK906 and GC140.</p

Water column speed.

<p>Vertical profile of mean speed (dark blue in the model and black lines in the observations) and standard deviation (light blue in ROMS and gray lines for the ADCP) averaged over the stations and corresponding model grid points shown in the inset.</p

Near bottom speed and zonal velocity.

<p>(a) mean speed; (b) maximum speed; (c) mean zonal velocity ; (d) maximum zonal velocity <i>u</i>_<i>MAX</i> at the model bottom layer. Unit: ms^-1. Black dots mark the coral locations. Bathymetric isolines as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156257#pone.0156257.g001" target="_blank">Fig 1</a>.</p

Immigration rates for two sympatric lineages of <i>L</i>. <i>glaberrima</i> among sites considered together and for Lineage 1 only.

<p>Immigration rates for two sympatric lineages of <i>L</i>. <i>glaberrima</i> among sites considered together and for Lineage 1 only.</p

Particles position.

<p>Particles position projected onto the horizontal plane 40 days after their release for each deep deployment overlaid bathymetry contours. Particles deployed at VK906 and VK826 are in blue, and particles deployed at GB299 and GC140 are in black.</p

Connectivity diagrams VK826 and GB299.

<p>Connectivity diagram for larvae released at VK826 and GB299. (a) No mortality term included. (b) Maximum competency period PLD = 20 days. Solid lines: Locations connected in all years (2010, 2011 and 2012). Dash lines: Locations connected in one or two years. Color indicates season. The percentage marked next to each arrow corresponds to the % of particles that reach the connected site.</p

Relative vorticity.

<p>(a) Surface and (b) near bottom relative vorticity snapshots in February 2011. Unit: s^-1. Positive values indicate cyclonic, anticlockwise motion, and negative anticyclonic, clockwise spin. Magenta dots in panel (b) mark the location of coral colonies. Bathymetric isolines as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156257#pone.0156257.g001" target="_blank">Fig 1</a>.</p

Model domain.

<p>ROMS was configured over the region for which the complex bathymetry is shown above. The Louisiana and Texas (LATEX) shelf and major canyons are also indicated. Lagrangian particles were then released within the areas marked by the red squares and allowed to disperse for 40 days.</p