Paragorgia arborea Linnaeus 1758

Paragorgia arborea (Linnaeus, 1758)

(Figs. 6–9)

Alcyonium arboreum Linnaeus 1758: 803.

Paragorgia nodosa Koren & Danielsen 1883 (sensu Bayer 1956: 70). Paragorgia pacifica Verrill 1922: G16.

Paragorgia arborea: Broch 1912: 6; Grasshoff 1979: 117 (and references therein).

Material examined: NIWA 3308, 33°55.6’S – 167°55.1’E, 1225 m, (Waipori, bottom trawling, Z10987), 23 January 2002, New Zealand; NIWA 3309, (J217), 33°55.6’S – 167°54.4’E, 955 m, (Waipori 1621/011, Z11009) 8 June 2002; NIWA Z10920 (J208)/ Z10956 (J212), (AEX 0101/080), New Zealand EEZ, exact locality unknown (probably near: 42°47’S – 179°32’E, 1077 m), (Kap Farval), 17 October 2001; NIWA 3310, Z9862 (J219), 44° 45.0S –174°50.0–49.0’E, 687–940 m, (Kap Farval 1278/102), 21 October 1999, New Zealand; NIWA 3311, X700 (J221), 35° 50.447’–49.900’S–177° 54.497–54.644’E, “Southern Havre trough” (dredge), 1525–1798 m, 12 February 1996, New Zealand; USNM 98045, 52° 17’– 52° 22’S –160° 40’– 160° 34’E, 659–798 m, (Eltanin R/ V 1414, USAP 16, U. Southern California, trawl­blake), 9 February 1965, New Zealand; USNM 52433, 54° 19’N – 159° 40’ W, (Albatross R/V 3338), 1143 m, 28 August 1890, Alaska, USA; USNM 1014919, Davison seamount, 1313 m, California 2003, USA.

Diagnostic characters. Surface cortex (including calyx surface) containing small, ornate, radiate sclerites (6, 7, and 8 rays); predominantly 6 radiates with distinctive, labyrinth­like, groove markings in the radiate projections or ornamentations (Figs. 7 C–D and 8C–D).

Description. Robust tree­like colonies up to several meters in height with bubble­like concentrations of autozooids (Fig. 6). Complete specimens exhibiting dense and regular accumulations of autozooid nodules or bulbs on distal or lateral branches, whereas the distal main stem and branches are usually without nodules (Fig. 6 A). Inter­nodular surface with numerous and uniformly distributed tiny siphonozooid apertures giving the colony a granular texture (Fig. 6 D). Medulla perforated by 5–7 main stem canals in terminal branches, surrounded by both red and colorless spindles; outer medulla with colorless sclerites and numerous smaller canals. Polyps completely retracted and enclosed within the calicular (small conical protuberance of the nodule) cortex. Tentacle sclerites are blunt, stubby ovals up to 0.1 mm (Figs. 7 A–B, 8A–B), commonly found in several Paragorgia spp. (Bayer, 1993), but some of them pointed like a spindle (Fig. 8 A). They have conical ornaments usually arranged bipolarly with a smooth neck, and at the surface exhibit a granular appearance due to microcrystal calcite tips. Radiate sclerites (6­radiate) from the surface are small, averaging 0.043 mm length in two different specimens, exhibiting low variation (0.004 SD, n=10, NIWA 3308; 0.002 SD, n=10, NIWA Z10920). Radiates 1.3 times longer than wide, averaging 0.03 mm in width (0.001 SD, n=10, NIWA 3308;

0.002 SD, n=10, Z10920) also occur. The rays are ornamented with distinctive markings (see diagnostic character) and the surface between is smooth. Subsurface rich in diverse radiates and intermediate forms between radiate and spindle attaining larger sizes (Figs. 7 F, 8E). Medulla sclerites long, slim spindles up to 0.5 mm length with irregular projections, some quite prominent (up to 0.02 mm) and bifurcated (Figs. 7 E, 8F). Occasionally slightly curved, intermediate forms (short and long ornamented spindles) present between the medulla and subsurface (see Grasshoff, 1979).

Morphological variation. Whereas sclerites and ultrastructure variation has been usually low among many specimens and geographical localities (e.g., Grasshoff, 1979), colonial features seem to have a great deal of variation. One New Zealand specimen (NIWA Z9566) had unusually large siphonozooids and autozooids with eight grooved notches in the aperture not present in the rest of the material, but no scleritic differences were found. Most New Zealand specimens were red except a few paler (pink) specimens. The size of the autozooid nodules was another factor of variation. Some specimens had nodules of less than 20 mm in diameter (e.g., Fig. 6 A–B) and some had up to 30 mm (Fig. 6 C–D), the latter corresponding to the largest specimens from the NIWA collection. However, only one specimen of this morphotype is fairly complete and no correlation with colony size can be made. Similar variation has been recorded in northern latitudes including the presence of white individuals (Tendal 1992), which have not been found in New Zealand.

Distribution. P. arborea has one of the most intriguing distributions among octocorals (e.g., Fig. 1), it has been abundantly collected and observed towards the two poles in the North Atlantic and in sub­Antarctic waters (Broch 1912) but no intermediate populations have been found so far. Tendal (1992) provided a complete compilation of P. a r b o re a records in the North Atlantic concluding that the species is usually distributed between 200 and 1330 m in depth and a temperature of 4–8 °C. In the Southern Hemisphere it has been reported from the Falkland Islands, on the Patagonian shelf. New Zealand records (e.g., 1525 m) are the deepest records for this species.

Species comparisons. Broch (1957) reported specimens of P. a r b o re a for the first time in the Southern hemisphere. Grasshoff (1979) reviewed material, including some SEM analyses, from boreal and austral latitudes concluding that they belong to the same species. The material collected and studied from New Zealand waters presented the same diagnostic characters and size variation presented by Grasshoff’s (1979) SEMs. The diagnostic characters of the surface radiate sclerites of P. arborea are not similar to any other Paragorgia species. Other scleritic characteristics are very similar to other Paragorgia spp. such as the polyp (tentacles) and medulla sclerites, but the diversity of forms in the subsurface is richer in P. arborea than in any of the studied species. However, it is still unknown if the boreal and austral populations of P. a r b o re a are indeed the same interbreeding population and if there are stepping­stone populations in the tropics; further genetic testing would help to solve this problem. An important variation within P. a r b o re a “populations” is present in the specimens from Alaska in the North Pacific, corresponding to P. pacifica Verrill (1922). The sclerites from a specimen from Alaska have the same diagnostic characters including the particular 6­radiates with grooved ornaments (Fig. 9 D) but the sclerites from the medulla seem to be reduced in size and ornamentation with respect to the New Zealand P. arborea (Figs. 7 F, 8F vs 9H). The surface sclerites (6­radiates) were also found to be smaller than the other Paragorgia species examined (Fig. 3). Paragorgia pacifica was described on the grounds of colony form and as Verrill (1922) stated, “there may be doubt whether P. pacifica is not a variety of P. arborea ”, because it was described without sclerite examination. Nevertheless, the North Pacific populations of P. arborea seem to be the most derived morphologically, but a more comprehensive revision including type material and genetics is needed before reaching conclusions on P. p a c i ­ fica and the differentiation of south vs north P. arborea populations.

m); H, sclerites from the colony medulla (scales 100 m).