Gobiodon spadix Sato & Motomura, 2024

Hildebrandt, Courtney A., , Catheline Y. M. Froehlich, , Ole B. Brodnicke, , O. Selma Klanten, , Peter R. Møller, Wong, & Marian Y. L., 2024, Two new species of Gobiodon (Teleostei: Gobiidae) from the Indo-Pacific, with notes on South Pacific and Indian Ocean populations of Gobiodon spadix, Raffles Bulletin of Zoology 72, pp. 488-510 : 500-504

Gobiodon spadix Sato & Motomura, 2024

English Name: Akane Coral Goby Japanese Name: Akane koban-haze ( Figs. 7–9; Tables 6, 7)

Materials examined. South Pacific: 3 specimens from One Tree Island , GBR (23°29.778′ S, 152°05.285′ E), collected at 1–2m depth by C. Froehlich and C. Hildebrandt in 2022. AMS I.51468-001, 32.5 mm SL. AMS I.51468-002, 36.1 mm SL. I.51468-003, 27.5 mm SL . 3 specimens from One Tree Island , GBR (23°29.778′ S, 152°05.285′ E), collected at 1–2m depth by C. Hildebrandt and S. O’Hea Miller in 2023. AMS I.51469-001, 30.2 mm SL. AMS I.51470-001, 38.3 mm SL. QM I.41388, 38.2 mm SL .

Japan: AMS I.51370-001 (Paratype), 33.0 mm SL, Ohto Beach, Kagoshima Prefecture, Japan, collected by M. Sato, 2022. KAUM I.156336, 37.0 mm SL, Take-shima [=Island], Kagoshima, collected by M. Matsuoka et al, 2021. KAUM I.168009, 25.7 mm SL, Take-shima, Kagoshima, collected by M. Matsuoka et al., 2022. KAUM I.163955, Mageshima [=Island], Kagoshima, collected by M. Yamada et al., 2021. KAUM I.99082, 29.7 mm SL, Akuseki-jima [=Island], Tokara Islands, Kagoshima, collected by Y. Fukui et al., on RV Nansei-maru, 2017. KAUM I.166757, 15.5 mm SL, Satsuma Peninsula, Bonotsu, Kagoshima, collected by M. Sato, 2022. KAUM I.184177, 35.1 mm SL, Yudomari, Yakushima [=Island], Kagoshima, collected by Y. Dewa, 2023. KAUM I.186861, 27.3 mm SL, Take-shima, Kagoshima, collected by A. Higuchi, 2023. OMNH-P 43085 , Ryukyu Islands, Okinawa, Japan, T. Suzuki, 2015. OMNH-P 430086 , Ryukyu Islands , Okinawa, Japan , T. Suzuki , 2015 .

Maldives: 8 specimens from Kandahalagalaa, Maldives, collected by O. Brodnicke, P. R. Møller and K. Worsaae, 2021. ZMUC P2398073 , 21.3 mm SL. ZMUC P2398100 , 25.7 mm SL. ZMUC P2398511 , 28.3 mm SL. ZMUC P2397923 , 32.2 mm SL. ZMUC P2398072 , 24.0 mm SL. ZMUC P2397997 , 22.3 mm SL. ZMUC P2398558 , 29.3 mm SL. ZMUC P2397939 , 32.1 mm SL . 2 specimens from Tilla, Maldives, collected by O. Brodnicke, P. R. Møller and K. Worsaae, 2021. ZMUC P2398287 , ZMUC P2398283 , 22.7 mm SL .

The original description of Gobiodon spadix suggests that the individuals of similar appearance originally described in Munday et al. (1999) as Gobiodon sp. D from Papua New Guinea and the Great Barrier Reef are members of this species ( Sato & Motomura, 2024). Our measurements and analysis of individuals from the southern Great Barrier Reef at One Tree Island (6 specimens) ( Fig. 7, 8), compared with a paratype held at the Australian Museum (1 specimen) and loaned specimens from Kagoshima University Museum (7 specimens) and Osaka Natural History Museum (2 specimens), confirm this distribution pattern. We provide the following additional measurements as representations of the South Pacific Ocean population for the summary diagnosis and additional remarks about differences seen in the southern population not included in the original description. Comparisons to similar-appearing individuals from the Maldives were also conducted but were inconclusive as they did not agree with previously conducted genetic analyses ( Sato & Motomura, 2024).

Summary diagnosis. Gobiodon spadix was originally described with the following characteristics: “dorsal-fin rays VI-I, 9–11 (modally 9); anal-fin rays I, 8 or 9 (8); pectoral-fin rays 19–21 (20); body depth at pelvic-fin origin 32.4–38.3% (mean 36.0%) of SL; distance between first dorsal-fin origin to dorsal-most point of pectoral-fin base 50.4–64.8% (55.2%) of HL; pectoral fin relatively long, length 90.6–112.5% (100.8%) of HL; groove between isthmus and interopercle absent; when alive or freshly collected, body uniformly reddish-brown; coloration of all fins darker than that of body; 5 vertical narrow bluish stripes on lateral surface of head.” ( Sato & Motomura, 2024).

The South Pacific Ocean population does display minor differences to their northern Pacific Ocean counterparts. Described from specimens collected from the southernmost extent of the Great Barrier Reef at One Tree Island, southern population measurement variations can be included in the diagnosis characteristics: dorsal fin rays VI –I, 9–10 (modally 10); pectoral fin rays 19–20 (modally 20); body depth at pelvic fin 34.9–40.8% of SL, pectoral fin relatively long, length 69.5%–93.9% of HL (average 85.2%). Additionally, some measurements have been provided in the common alternative format as percentages of standard length rather than head length: distance between first dorsal fin origin to dorsalmost point of pectoral fin base 13.2–17.5% of SL and pectoral fin length long at 19.5–30.1% of SL.

Supplementary details include absent post-symphysial canine teeth, triangular dentary shape of two to three sizes in several rows, short cheek papillae, and the presence of two additional pale blue lines behind the pectoral fin but not extending beyond this point as seen in other species such as G. rivulatus . Photographs and radiographs of a representative specimen from the South Pacific Ocean population can be seen in Fig. 7. Papillae and pore maps can be seen in Fig. 8. Summaries of the morphological measurements and meristics can be found in Tables 6 and 7 respectively.

Remarks. There are slight differences in the host coral choices between the two populations. Gobiodon spadix was described in Sato & Motomura (2024) as being hosted by the corals Acropora solitaryensis Veron & Wallace, 1984 and A. japonica Veron, 2000 (in Veron & Stafford, 2000). However, members of the species have been seen being hosted by Acropora divaricata ( Dana, 1846) and Acropora solitaryensis in the South Pacific Ocean ( Munday et al., 1999, Hildebrandt, pers. obs.). Whilst the distribution of A. divaricata does include the areas of Japan where G. spadix can be observed, it is not a dominant coral seen in Japanese coral reefs ( Veron et al., 1976). Acropora japonica is, however, a dominant component of coral reef communities within the Northern Pacific Ocean surrounding Japan, though it is not commonly found outside this region ( Veron et al., 1976). Therefore, these differences in coral distribution could explain the differences seen in host coral between the populations of G. spadix . However, A. japonica does have a significantly different growth form when compared to the more bush-like structures of A. solitaryensis and A. divaricata . The table-like growth form seen in A. japonica has been known to host Gobiodon species, with corals such as Acropora gemmifera ( Brook, 1892) , Acropora digitifera ( Dana, 1846) , and Acropora humilis ( Dana, 1846) frequently hosting G. rivulatus , G. quinquestrigatus , and G. fuscoruber ( Munday et al., 1999; Untersteggaber et al., 2014; Wehrberger & Herler, 2014).

There are also several small morphometric differences between the two populations. However, these are not different enough to delineate them as separate species. Noticeable differences can be seen in the head length and depth measurements, with members from the South Pacific Ocean population typically displaying reduced head depth and increased head length compared to the Japanese population. Some minor meristic counts differ too, with the second dorsal fin ray count being slightly higher, modally 10 in the South Pacific Ocean population compared to 9 in the Japanese population. Whilst not major differences, they are points of interest that should be observed to monitor the differences between the two populations of this species.

Individuals of the South Pacific Ocean population have a smaller pectoral fin length (69.5%–93.9% of HL, average 85.2%) than the Japanese individuals (91.4–104.4% of HL, average 95.9%) measured in this analysis. Gobiodon quinquestrigatus measured in this study displayed highly similar ranges (78.4–99.8% of HL, average 84.2%) to members of G. spadix in the South Pacific Ocean. Therefore, pectoral fin length as a proportion of head length may not be a suitable distinguishing feature between G. spadix and G. quinquestrigatus . However, the two species differ in interorbital width, snout length, and snout to pelvic length. Additionally, when the overall set of morphological measurements are combined in a PCA, there are sufficient differences between G. spadix and G. quinquestrigatus to confirm their status as separate species. This has been previously suggested by their physical appearance and genetics ( Munday et al., 1999; Duchene et al., 2013; Herler et al., 2013; Hing et al., 2019).

Individuals with a similar description to G. spadix have also been observed in the central Indian Ocean on reefs surrounding the Maldives. Genetic testing conducted by Sato & Motomura (2024) suggest that these individuals are placed somewhere between G. spadix and G. quinquestrigatus when analysed using 16S rRNA. Sato & Motomura (2024) assigned these individuals the holding name Gobiodon sp. A . This separation between similar-appearing individuals from the Pacific Ocean and Maldives was also detected in an analysis of 12S and 16S rRNA conducted by Herler et al. (2013). The observed proportional morphometrics of the individuals originating from the Maldives displayed slightly larger variation than that seen between the Japanese and GBR specimens ( Fig. 9). However, there was still considerable overlap of the 95% confidence intervals and individuals of all three groups intermixed in the central area of the principal coordinates analysis (PCoA). Both the morphometrics conducted here and the previously conducted genetic analyses suggest that further research will need to be conducted to determine the relationship between the individuals observed in the Maldives and the recently described G. spadix .