“28. Primnoa Lamouroux, 1812
FIGURE 13H–P
Primnoa Lamouroux, 1812:188.—Studer, 1887:49.—Wright and Studer, 1889:xlviii.—Versluys, 1906:84–85.—Kükenthal, 1915:143 [key to genus]; 1919:357–360 [key to genus]; 1924:265–266 [key to genus and species].— Bayer, 1956:F220; 1961:294 [illustrated key to genus]; 1981b:937 [key to genus].—Bayer and Stefani, 1989:454 [key to genus].—Cairns and Bayer, 2005:226–228 [revision and key to species].
Lithoprimnoa Grube, 1861:174–175.
Diagnosis. Colonies dichotomously branched and usually bushy, some reaching a height of 2 m. Calyces closely spaced and randomly arranged on all branch surfaces, the appressed calyces facing downward. Well developed operculum present, the operculars keeled on inner surface. Polyps large and fleshy, each polyp protected by two rows of four or more large abaxial scales, sometimes arranged in an irregular manner, two short inner-lateral rows of two or three smaller scales (including the marginals), and two even shorter rows of two (including the marginals) adaxial scales, resulting in six longitudinal rows, but four of them composed of very small and few scales; adaxial side of body wall predominantly bare (Figure 13i). There is also a crown of eight large, concave marginals, the adaxial marginals usually smaller than other marginals. Coenenchymal scales arranged in one layer. Tentacular rods are often present (Figure 13j).
Discussion. The four Recent species and one variety (Table 4) in this genus were described, illustrated, and keyed by Cairns and Bayer (2005); the two Paleocene fossil species listed in Table 4 from Denmark (Nielsen, 1913, 1925) are highly doubtful identifications, Bayer (1992) synonymizing one of them, P. gracilis, with the lithotelestid Epiphaxum auloporoides (Lonsdale, 1850). Characters used to distinguish species include the size and shape of the basal scales, size and shape of the polyps, and the shape of the marginal scales. Distribution patterns (Watling and Auster, 2005) and characteristics of the massive axis of this genus have been the subject of many studies, including aspects of growth rate (Andrews et al., 2002), and paleoceanographic isotopic analysis (Heikoop et al., 2002; Sinclair et al., 2005; Sherwood et al., 2005).
Distribution. North Pacific, North Atlantic, subantarctic South Pacific, 9–1,020 m.
Type Species. Primnoa: Gorgonia lepadifera Linnaeus, 1767 (= Gorgonia resedaeformis Gunnerus, 1763), by monotypy. Type not traced.
Lithoprimnoa: L. arctica Grube, 1861, by monotypy. Type not traced.”
(Bayer & Cairns, 2009)
“Subclass Octocorallia
Order Gorgonacea
Suborder Calcaxonia
Family Primnoidae Gray, 1858
Primnoa Lamouroux, 1812
Primnoa Lamouroux, 1812: 188; 1816: 442.—Kükenthal, 1919: 357–360; 1924: 265–266 (references).— Bayer, 1956: F220, fig. 157, 1.
Lithoprimnoa Grube, 1861: 174–175
Type species.—Primnoa: Gorgonia lepadifera Linnaeus, 1767 (=Gorgonia resedaeformis Gunnerus, 1763), by monotypy.
Lithoprimnoa: Lithoprimnoa arctica Grube, 1861, by monotypy.
Diagnosis.—Dichotomously branched, arborescent Primnoidae with polyps not arranged in whorls but closely crowded on all sides of the twigs and branches; polyps distinctly curved downward toward the axis. Polyps adaxially naked or nearly so, abaxially armed with scales or plates of variable size, shape, and arrangement. Marginal scales eight, those of the adaxial side of the polyp smaller than those of the abaxial side and may be only indistinctly differentiated. Operculum strongly developed, the adaxial pair of scales smaller than the abaxials and laterals. Tentacles with small, thorny rods.
Remarks.—Kükenthal (1919) recognized only one species of Primnoa, P. resedaeformis, and a variety of it, P. pacifica, a view shared by Madsen (1944). Kükenthal later (1924: 267) treated P. pacifica as a subspecies of the North Atlantic P. resedaeformis: “P. resedaeformis typica.” Both Kükenthal (1924) and Aurivillius (1931) treated P. willeyi as a dubious species, the former considering it probably synonymous with P. resedaeformis.
Broch (1935: 29–33) discussed the status of P. pacifica relative to P. resedaeformis, concluding that the Pacific species is a geographical form of the Atlantic species. His investigation of Norwegian specimens from Trandhjemsfjord showed that the variability of polyp scales is considerably less than in Pacific colonies, and that strongly developed “Basalscleriten” are almost never (“fast nie”) seen in Norwegian colonies. While visiting the Natural History Museum, London, FMB was able to make a drawing of a branch of Hickson’s original material of P. willeyi (Fig. 7C). No type material of P. pacifica is available to us, but samples collected in Japanese waters agree with Kinoshita’s description in most respects and may be taken as representative of his concept.
Specimens of Primnoa trawled in the Pacific sector of the Southern Ocean by USNS ELTANIN are the first record of the genus from Subantarctic waters, although this taxon was reported as a nomen nudum by Heikoop et al. (2002) and Risk et al. (2002). This material demonstrates unequivocally the bipolarity of the genus Primnoa. The few North Pacific specimens available for study show consistent differences from North Atlantic specimens. The numerous specimens from three stations in the Southern Ocean likewise differ somewhat from both North Pacific and North Atlantic specimens.
Kinoshita (1908a) already has remarked upon the Narella-like development of the basal scales in P. pacifica. Pacific specimens of Primnoa in the present collection carry the similarity of the two genera even further. Polyps of a very young colony from the Alexander Archipelago of southern Alaska (USNM 58397) are enclosed in a pair of large, Narella-like basal scales that form a pair of projecting flat horns, a pair of somewhat smaller medial scales, and a circle of buccal scales of which the abaxial pair commonly are the largest. These polyps (Fig. 5A–B, USNM 58397) have a strikingly Narella-like aspect, closely approaching in form the polyps of those Narella species having strongly developed adaxial buccal scales, such as Narella megalepis (Kinoshita, 1908). The most obvious distinction of Primnoa from Narella is the presence of more than four scales in the buccal ring, and the crowded, non-verticillate arrangement of polyps.
Most polyps of North Atlantic colonies of P. resedaeformis have two main rows of large abaxial scales between the marginal scales and the basal scales, the latter of which are not strongly developed and not especially conspicuous. The polyps of Pacific colonies have more numerous, more or less irregularly placed scales between the marginal and basal scales, which usually maintain or increase their size to a variable extent, commonly projecting outward as a pair of strong processes or flat spines.
Although interbreeding populations could be expected to exist around the northern perimeters of the North Pacific and North Atlantic, it is not known at present whether or not the two areas are linked by a continuous population around the Polar Sea (see Broch, 1949). Similarly, it is not known whether or not a continuous population extends from the North Pacific to the South Pacific. Not all possible localities have been sampled by dredge or observed by submersible at appropriate depths. However, the broad scope of explorations at low latitudes in both Pacific and Atlantic Oceans over the past century might have been expected to discover evidence of intermediate populations had such existed.
KEY TO SPECIES AND VARIETIES OF PRIMNOA
1 . Basal scales of most polyps larger than medials, and usually with a prominent marginal spine (Narella-type scale) ..........(P. pacifica) 2
1´. Basal scales roughly the same size as medials, never with marginal spines ..........3
2 . Polyps long and fleshy, often twisted and lacking sclerites on lateral edges of polyps; ratio of mid- to distal polyp diameter 0.25–0.43 .......... P. pacifica var. willeyi
2´. Polyps more robust, straight, with small body wall sclerites on lateral surfaces of polyps; ratio of mid-distal polyp diameter 0.53–0.67 ..........P. pacifica typical
3 . Abaxial medial scales large (to 1.5 mm wide), rectangular, and arranged in 2–5 pairs ..........P. resedaeformis
3´. Abaxial medial scales smaller, elongate or elliptical, not arranged in pairs ..........4
4 . Medial scales elongate and slender (< 0.2 mm wide), restricted to a narrow abaxial tract that is immersed in tissue; operculars spatulate; marginals extremely concave; tentacular rods large and often curved; Aleutians ..........P. wingi sp. nov.
4´. Medial scales elliptical to square (up to 1.0 mm wide), covering abaxial and lateral polyp surface; operculars isosceles-triangular; marginals flat; tentacular rods smaller and straight; Subantarctic ..........P. notialis sp. nov.”
(Cairns & Bayer 2005)
Primnoa (Lamororux, 1812) also known as red tree coral, is a genus of soft corals and the type genus of the family Primnoidae (Milne Edwards, 1857).[1] They are sessile, benthic cnidarians that can be found in the North Pacific, North Atlantic, and Subantarctic South Pacific,[2] and its members often play a vital ecological role as keystone species[3] within their environment as a habitat and refuge for the megafauna that also inhabit those regions.[4] This, in combination with their slow growth, makes the increasing disturbance to their habitats caused by fishing activities particularly impactful and difficult to recover from.[5]
The name Primnoa derives from the Greek word Πρυμνὼ (Prymno),[6] the name of an Oceanid. The name itself is derived from πρυμνός (prymnos), meaning “last”, “lowest”, and by extension, “deepest”.[7]
The genus Primnoa was first described by Jean Vincent Félix Lamouroux in 1812.[5] In the 19th and 20th century, several more species were proposed as members of Primnoa, but most were originally described as members of other genera within Primnoidae. Currently there are only five valid species and one variety that are recognized members of the genus.[1][8] Their details are tabulated below:
Primnoa colonies are typically bushy in shape, heavily branched with no immediately visible main stem, though they do possess one. They also dichotomously branch, meaning that they separate into two equally sized branches at every branching point.[10] They have large polyps that are non-retractile which are protected by a polyp composed of six overlapping rows of calcitic scales, with adaxial (stem-facing) scales tending to be smaller than their outward facing counterparts, or absent altogether.[2] Polyps are individually distinct, usually appressed and downward facing, but otherwise randomly arranged and close together.[9] Due to their predatory nature, most have small, thorny tentacles, and a well-developed operculum at the tip of the polyp.[11] Primnoa are monomorphic, thus only having one type of polyp. Their internal anatomy is consistent with that of other gorgonian corals.[12] The physical differences between species in this genus primarily derive from variances in body scale shape and number. Species in these genus have colors that range from pink to reddish-orange.[8]
They are also ahermatypic, which means they aren’t reef building corals, but they still form large structures and are found in abundance in clusters of colonies.[13] Like many other octocorals, rather than using calcium carbonate in the form of aragonite (which is used by Scleractinian corals), Primnoa use a more stable form called calcite, which is less soluble in seawater. They anchor themselves to hard substrates using calcareous discoid holdfasts, which are then further supported by growing layers of calcite at the base of the colony.[5]
Not much is known about the reproduction of Primnoa species. So far, it has been established that Primnoa are gonochoristic corals, meaning that each colony is either male or female.[12] Reproduction occurs via broadcast spawning, which results in the organisms externally fertilizing their eggs. Unlike most corals which use this method, there is no evidence of reproductive periodicity or synchronized mass spawning events.[14]
Like many other deep-water corals, Primnoa are azooxanthellate, meaning that they do not have symbiotic relationships with Symbiodinium. Instead, they received nutrition via filter-feeding and obtain food directly from the water column.[15] Studies suggest that Primnoa are primarily carnivorous, feeding on sinking particulate organic matter and zooplankton. The possibility of them eating resuspended meiofauna has also been proposed, given their downward facing polyps.[13]
Many species of Primnoa are considered ecologically important, acting as keystone species, foundation species, and ecological engineers because their complex branching and large size allow them to serve as a habitat by providing shelter and substrate for many animals.[16][5]
Some species of suspension feeders use the branches of Primnoa to obtain nutrients, by elevating their position in the water and collecting floating particles that circulate the water column,. These species include various crinoids, basket stars, anemones, and sponges. Suspension feeders have been reported in association with Primnoa at depths greater than 300 m.[4]
Species also seek shelter and protection using the branches of Primnoa to hide them from predators. These species include types of crabs, shrimps, and rockfish. Shrimp are observed to be hiding among the polyps of the corals, while crabs were found beneath them. Rockfish were found both beneath and among the polyps. In some circumstances, species were found to be using the protection of the coral polyps for reproductive purposes, as they were well hidden from predators among the coral’s branches.[4]
Predators of the Primnoa include sea stars, nudibranchs, and snails, though sea stars are their primary predators. One study found that sea stars were responsible for 45-34% of the consumption of the soft coral polyps.[4]
Primnoa require hard substrate they can firmly attach to, such as rocky outcrops or boulders. These hard substrates allow them to live in areas with strong currents, a preference which increases their odds of capturing food due to the higher velocity and volume of water passing through their branches.[5][12]
Despite being characterized as deep water corals, Primnoa can also be found in shallow water habitats. The total bathymetric range occupied by the genus is between 6-1,020 m.[2] However, Primnoa being present in these shallow regions is due to a phenomenon known as deep-sea emergence, which is defined as “a phenomenon whereby organisms that typically dwell in the deep sea are able to exist in shallow-water areas because of unusual oceanographic conditions there.”[17] In this case, retreating glaciers have resulted in exposed bedrock and very cool temperatures that are similar to the deep-water temperatures preferred by Primnoa, as well as other factors that help mimic their natural environment.[12] Additionally, one study observed how some coral grew in atypical forms due to poor health, causing them to become ecomorphs due to the stress of living in unfavorable conditions such as turbidity and periods of increased water temperature higher than they could tolerate.[17]
The Aleutian Islands are an island chain off the coast of Alaska, in the North Pacific. They range approximately 6,821 square miles, and are made up of around 300 islands, including 14 larger volcanic islands. The waters are cold and nutrient rich due to the active margins they inhabit, and experience large amounts of upwelling from the seafloor.
The benthic environments in which Primnoa are found provide the capacity for unique and highly diverse sponges and soft corals. These organisms in turn provide the basis for a habitat to many vertebrate species such as fish. This region is home to the most productive fisheries of the Northern Pacific due to the benthic abundance and its capacity to support vertebrate species. In general, corals are most abundant at depths between 100 and 200 m, but can be found anywhere from 27 to 363 m down.[18]
19 species of corals known in the Aleutian Islands belong to the Primnoidae family, and 25 of the 69 documented species of corals in the Aleutian Isles, including P. wingi are endemic species.[2][19] Meaning they are restricted to the geographical range that spans the Aleutian Islands; however this diversity begins to increase west of 169°W.[19] It is believed by some scientists that the Aleutian Islands serve as the evolutionary cradle for some taxa of cold water soft corals, due to the sheer diversity and abundance of the organisms that the waters display.
The largest risk for this family of corals comes from fisheries and net trawling, which uproots the corals and destroys them. Sometimes, the corals are worn by natives as jewelry, as they are bycatch of the fishing hawks and do not have other nutritive or practical uses. Nearly 39% of the seafloor of the Aleutian Islands shows disturbance due to bottom-contact fishing tools and gear such as nets.[18] Because of their vital interactions with megafauna in these ecosystems, fisheries must integrate coral conservation into their practices, or otherwise risk disturbance to their entire industry.
{{cite book}}: CS1 maint: date and year (link) Primnoa (Lamororux, 1812) also known as red tree coral, is a genus of soft corals and the type genus of the family Primnoidae (Milne Edwards, 1857). They are sessile, benthic cnidarians that can be found in the North Pacific, North Atlantic, and Subantarctic South Pacific, and its members often play a vital ecological role as keystone species within their environment as a habitat and refuge for the megafauna that also inhabit those regions. This, in combination with their slow growth, makes the increasing disturbance to their habitats caused by fishing activities particularly impactful and difficult to recover from.
