Paragorgia arborea
Paragorgia arborea is a species of coral in the family Coralliidae, commonly known as the tree bubblegum coral. It mainly grows in depths between at temperatures between. It is found widespread in the Northern Atlantic Ocean and Northern Pacific Ocean on seamounts and knolls, and was first described by the Swedish naturalist Carl Linnaeus in 1758. P. arborea is a foundation species, providing a habitat for other species in deep sea coral ecosystems.
Description
Paragorgia arborea can grow to heights of, and are brightly colored white, red, or salmon, in a branching, fan-shaped structure with a tough central trunk and many branches. The branch tips are bulbous, giving this octocoral its common name of bubblegum coral. It has both specialized feeding polyps, autozoids, and specialized reproductive polyps, siphonozoids. Little is known about the growth rate and life span of P. arborea, but it has been found to have an average growth rate of 1cm/yr, with growth rates of 2-6cm/yr found in some cases, and is long-lived on the scale of decades.Reproductive strategy
Like other deep-water corals, little is known about the specific reproductive ecology of P. arborea. It is hypothesized that P. arborea is a brooder - fertilization takes place on or inside the female colony. Corals reproduce sexually by either spawning or brooding, but then once settled, corals reproduce asexually to grow into a many branched colony.Feeding strategy
P. arborea is a filter feeder; it eats organic matter suspended in the current it lives in. It optimizes nutrient uptake by adjusting its behavior to the tidal cycle. When the tidal currents are coming in, coral polyps extend to actively feed on the organic matter being brought in with the tide. After the tide has gone out and the currents aren't bringing in as much organic matter, the coral polyps retract to digest the food or be inactive. Furthermore, P. arborea is often found growing in a concave shape facing into the current, which is a growth strategy thought to allow the coral to receive food more effectively.Microbiome
Because it is difficult to access deep sea corals for study, relatively little is known about the microbiome of P. arborea. It has been found to have a host-specific microbiome and an external surface mucopolysaccharide layer, which is a mucus that acts as a defense against water-borne pathogens and helps the coral filter feed. Alphaproteobacteria, Mycoplasmatota, and Spirochaetota are the main taxonomic groups of bacteria found in the P. arborea microbiome.Distribution and habitat
Paragorgia arborea is found between 30° and 70° latitude in both hemispheres. It is well established in the North Atlantic Ocean where it generally grows at depths between and at temperatures between. It occurs along the entire Norwegian coast, and at depths of in Norwegian fjords, especially those with poor visibility and abundant planktonic life. In the Western Atlantic, it occurs in Nova Scotia waters including Oceanographer Canyon, off Georges Bank, the Grand Banks, Davis Strait, and southern Greenland. It is also found near the Mid-Atlantic Ridge south of Iceland.P. arborea often grows on reefs created by the stony coral Lophelia pertusa. Like other gorgonians, it prefers exposed locations with strong currents. Thus, is most commonly found in marine canyons and on the continental slope, where the slope is steep. P. arborea prefers to grow on top of hard substrate that is a mixture of pebbles, boulders, and cobbles.