Protoreaster lincki ( de Blainville, 1830 )

Mah, Christopher L., 2023, A new species of Astrosarkus from Western Australia including new Mesophotic occurrences of Indian Ocean Oreasteridae (Valvatida, Asteroidea), Memoirs of Museum Victoria 82, pp. 143-165 : 160-162

Protoreaster lincki ( de Blainville, 1830)

Figure 11a–e

Asterias lincki de Blainville 1830: 238 ; 1834: 219

Pentaceros muricatus Gray 1840: 277

Oreaster muricatus Dujardin and Hupe 1862: 383

Oreaster reinhardti Lütken 1864: 159 ; Bell 1884: 74.

Oreaster lincki Lütken 1864: 156 ; Bell 1884: 72; H.L. Clark 1923: 273.

Pentaceros reinhardti Perrier 1878: 24 ; Sluiter 1895: 56; Koehler 1910: 101.

Protoreaster lincki Döderlein 1916: 423 ; 1936: 328; Tortonese 1949: 33; Kalk 1954: 113; Macnae and Kalk 1962: 108; Balinsky 1958: 1969; Kalk 1958: 215; 1959: 21; Day 1969: 182; A.M. Clark and Rowe 1971: 54; Jangoux 1973: 23; A.M. Clark and Courtman-Stock 1976: 68; Julka and Das 1978: 346; Marsh 1976: 222; Sloan et al. 1979: 722; Ebert 1979: 72; Tortonese 1980: 11; Aziz and Jangoux 1984: 137; A.M. Clark 1984: 90; Jangoux and Aziz 1984: 860; Walenkamp 1990: 51; Aziz 1986: 323; Marsh and Fromont 2020: 435.

Diagnosis. Body strongly stellate (R/r=2.3–3.0), arms triangular in shape, disk and arms thick, strongly arched, triangular in cross-section. Surface covered by smooth pavement of flat, polygonal granules. Primary circlet on disk with prominent spines, this area divided into five triangular regions. Reticulation across abactinal surface with well-developed reticulation surrounding areas with numerous papular pores, including five triangular regions on disk. Distal superomarginal plates with prominent laterally projecting tapering spines or knobs. Inferomarginal spines/tubercles absent. Bivalve pedicellariae present on a minority of marginal plates. Modified from Marsh and Fromont (2020).

Comments. Although recognised primarily as a near-shore, shallow-water species, previously documented at 0–10 m depth (Marsh and Fromont, 2020), one specimen collected from Madagascar was recorded from 40 m, a mesophotic and currently the deepest-known occurrence .

Marsh and Fromont (2020) indicated that it feeds on microbial biofilms and opportunistic scavenging. Ebert (1976) reported this species spawning in the Seychelles in early May and in northwestern Australia during November.

Shrimp associates such as Zenopontonia (formerly Periclimenes ) have been observed in association with this species ( Bruce, 1982).

Occurrence. Western Indian Ocean. Red Sea, Sri Lanka, Mozambique, Java, Indonesia. Northwest Australia, 0–40 m.

Material examined. IE-2007-3947, Madagascar, 25° 45.7" S, 44° 52.0" E. 41.0 m. Coll. N / O Nosy Be, 13 May 2010. 1 wet spec. R =8.8, r=3.3.

Discussion. The Oreasteridae surveyed herein as well as many other asteroid species in the Indo-Pacific region (e.g. Mah, 2017, 2018, 2021) are present at much deeper depths than recorded previously (e.g. 0–10 m for P. lincki [Marsh and Fromont, 2020] versus 40 m herein). The oreasterids surveyed here are widespread, ranging from the Indian Ocean (e.g. P. lincki or C. schmideliana ) to throughout the Indo-Pacific (e.g. A. idipi , P. alveolatus ). This combination of widespread distribution and extending into the mesophotic is a trend observed in other shallow-water tropical asteroid Valvatida , such as in the Goniasteridae (e.g. Fromia ), the Ophidiasteridae (e.g. Linckia ) and the Asterodiscididae (e.g. Asterodiscides ) ( Mah, 2021). Distributions of these taxa remain largely shallow (<200 m), with only some taxa exceptionally extending much deeper (e.g. Asterodiscides can occur to 800 m).

Most oreasterids surveyed here appear to be extensions of shallow-water asteroid faunas, that is, species displaying a wide bathymetric range, a pattern also observed in other taxa, such as corals and fishes ( Kahng et al., 2016). Food may be one important consideration, as numerous accounts have observed the widespread presence of benthic communities dominated by algae, sponges, cnidarians and other encrusting or colonial organisms (e.g. Harris et al., 2021; Bell et al., 2022). Observations of shallow-water oreasterid taxa, including C. granulatus , Protoreaster , and Culcita spp. have indicated food preferences consistent with bottom fauna observed at these depths, particularly sponges and microalgal biofilms, all of which appear to be tied to the lower limit of photosynthesis.

Astrosarkus ( Fig. 2a–d , 3a–b ) has been observed in close proximity to multiple sessile taxa, including cnidarians and sponges ( Fig. 3a ).

Bathymetrically, Astrosarkus stands apart in occurring at greater depths (67–210 m) than other mesophotic Oreasteridae (0–100 m, only exceptionally to 275 m). The most prominent feature that sets Astrosarkus apart from other oreasterids is its thick, soft body wall, which is unique within the Oreasteridae . Members of the family Poraniidae display a similar type of strongly developed soft-tissue body wall (Mah and Foltz, 2014). This character is poorly understood, but all living poraniids are known from cold-water settings ( Mah and Blake, 2012) suggesting that this character could be constrained or influenced by colder-water habitats. Astrosarkus ’ unusual body wall could be influenced by its depth, because the mesophotic zone is cooler than shallow tropical settings in the 0–100 m zone.

Based on the taxa surveyed herein, oreasterids appear similar to other mesophotic faunas (e.g. fishes, sponges, gorgonians; Baldwin et al., 2018, Idan et al., 2018, respectively) in being a mix of shallow-water taxa with a minority of taxa, in this case Astrosarku s spp., that are limited to a mesophotic distribution ( Breedy and Guzman, 2013). Other asteroid groups, including the Ophidiasteridae , Goniasteridae , and Asterodiscididae , with similar mesophotic distributions (i.e. they do not occur in shallow, surface-level habitats), have been reported from the South Pacific ( Mah, 2021). As further taxonomic groups are surveyed, it is hoped that better understanding of mesophotic species will provide a stronger basis for understanding diversity and establishing marine conservation in this setting.

Figures

Figure 2. Astrosarkus idipi. Maldives/Mayotte. a, Astrosarkus idipi (white/red form) from Mayotte, 75 m. Photo courtesy Thierry Mayotte; b, Astrosarkus idipi (white/red form) from Maldives. Photo courtesy Paris Stefanopoulis; c, Astrosarkus idipi (orange form) from St. Leu, Reunion Island. Photo by Patrick Plantard; d, Orange form with white highlights from Lifou Island, New Caledonia. Photo courtesy Laurent Ballesta.

Figure 3. Astrosarkus spp. from Australia. a, Astrosarkus sp. Northern Depths, Great Barrier Reef; b, Astrosarkus idipi from Coral Sea Marine Park. Distance between lasers is 10.0 cm.

Figure 11. Protoreaster lincki. MNHN IE-2007-3947. a, Abactinal view. Scale bar=1.5 cm; b, Abactinal-lateral view showing degree of spination and disk and arms. Scale bar=0.5 cm; c, Armtip showing carinal and superomarginal spines. Scale bar=1.0 cm; d, Actinal view. Scale bar=1.5 cm; e, Closeup of oral region and adambulacral spination. Scale bar=0.5 cm.