To the uninitiated, the mesophotic coral reefs would seem like an unlikely place to find vibrant fish life. Antonymous to the ebullient habitat of shallow water coral gardens, the mesophotic zone is a gloomy contrast of seemingly endless dread and forlorn landscapes. Except not quite. This realm straddles the divide between light dependent and light independent organisms, serving as a transition between two highly disparate dimensions. This “twilight zone” in return offers the world a glimpse of some incredible reef life, hidden behind the facade of this funereal bleakness.
Earlier this year, Brian Greene, Luiz Rocha and the California Academy of Sciences sampled the mesophotic reefs of the Philippines, returning with great yields in terms of new, scientifically unrecognized species. Amongst the incredible haul was a Grammatonotus sp with a stunning leaf shaped caudal fin; a fish that took the digital fish world by storm.
Just last week, Brian Greene wrapped up yet another dive into the dreary domain of the twilight zone. This time he was accompanied by Drs. Richard Pyle and Sonia Rowley; two authorities in their respective fields of ichthyology and gorgonian research. The survey took place in Pohnpei, part of the Senyavin Islands within the Federated States of Micronesia. Throughout their expedition, Brian and Sonia have been drip feeding short clips and photos of their dives, which included footage of some incredible, lesser seen species in situ such as Chromis circumaurea and Cirrhilabrus earlei.
What wasn’t shown, however, was a taxonomic deluge of undescribed fish species that rivals some of Brian’s best trips to date. The collection comprised significantly of Anthiines and Callanthids from the genus Odontanthias and Grammatonotus respectively, although several potential new species from Pseudanthias and even Tosanoides were documented.
The genus Odontanthias is subject to a rather confusing taxonomic history in the aquarium trade. For a long time, the genus was either used synonymously with Holanthias, or spelled incorrectly as Odanthias. It should be known that Holanthias is a genus of Anthiines comprising of two species, both of which are strictly confined within the Atlantic.
Two rather exciting and potentially undescribed Odontanthias were sampled and collected by Brian in Pohnpei. The first phenotype is characterized by having an elongated, filamentous extension on the third dorsal spine. This characteristic is quite unique, with only one species sharing this feature. It is Odontanthias flagris. The new Pohnpeian Odontanthias differs, however, quite significantly.
The ground coloration is a bright orchid purple and remains relatively unmarked, sans a few nondescript yellow striae. The dorsal, pelvic and anal fins are bright yellow, invading slightly into the facial region where it forms a vestigial mask. The caudal lobes are rounded and the fin is entirely purple. Like the soft dorsal fin, the caudal fin is threaded with soft, filamentous extensions.
This phenotype was collected from 430-450 ft in Ant Atoll, along the Southeastern side of Pohnpei. It is quite likely that this species turns out to be a distinct species, but whether or not it shares a cladistic relationship with O. flagris from the Ryukyus is another question subject to a higher degree of study and testing.
A second Odontanthias was recovered from the same location as the preceding. This fish draws a more familiar resemblance to the Japanese O. katayamai, although slight differences in coloration and biogeography suggests that this species may be genetically and taxonomically distinct. Both sexes of this phenotype were collected. In the females, the caudal fins are firey yellow, seemingly darkening into a rich cadmium orange in large males.
The ground coloration is a diffused blend of maraschino and magenta, with a series of yellow dots arranged in a horizontal linear fashion across the body. These dots converge towards the dorsum and bleed into the facial region forming a more complete mask. A streak runs along the lower orbital limit across the operculum and into the pectoral fin base. Its pelvic fins and all median fins are embellished with filamentous extensions.
This phenotype was also collected from 450 ft in Ant Atoll, along the Southeastern side of Pohnpei. It shares the same habitat as the preceding species. Above is an image of O. katayamai from Okinawa. While the resemblance between the Pohnpeian phenotype and the Japanese type species is uncanny, there are major differences observed in the median fins. Specifically the caudal fin. In O. katayamai, this fin is flag-like and trimmed in yellow. In the Pohnpeian phenotype, this fin remains unmarked.
A pair of Pseudanthias resembling P. rubrolineatus were also collected. P. rubrolineatus has an unusually wide but scattered distribution across the Pacific. The type specimen was known from New Caledonia, but the species is most often seen and documented in Japan, where it can be found in relatively shallower depths at 200ft. This species, phenotypically at least, resembles P. fasciatus very closely in having a horizontal medial stripe. In P. rubrolineatus, this stripe emerges from an operculum band at a 45° angle before tapering horizontally into the upper caudal peduncle.
In examining numerous specimens online, it appears that the fish generally possesses hyaline caudal and pelvic fins. A single specimen from Tokara, 650ft, however, displays an unusual amount of erythrism on these fins. Its unclear if this red is a direct correlation to sexual maturity, or simply a post mortem artefact. In Brian’s Pohnpei specimens, only the male possesses the red fin pigments, suggesting that this might indeed be sex linked.
As previously mentioned, this species is wide ranging but poorly documented due to its deepwater nature. Despite the phenotypic homogeneity between the Miconesian, New Caledonian and Japanese specimens, it will be interesting to see if there is any genetic connectivity between all of them. Seeing as all three locations harbour unique fauna in their respective ecoregions, it’s possible that Pseudanthias rubrolineatus is a complex of cryptic species that are in the incipient stages of genetic divergence. But for now, whether or not this Pohnpeian specimen represents a simple range extension or a possible new taxa is subjected to more scrutiny.
The specimen was collected one mile off Palikir Pass, Pohnpei, at 350ft. Brian reported seeing dozens at this location.
Another exciting Anthiine documented from the same reef is an apparently new Tosanoides. This is a small genus comprising of two species; T. flavofasciatus and T. filamentosus. Tosanoides is very deepwater and primarily Japanese in distribution; although T. flavofasciatus has been found outside of Japan in Palau. It is very likely that both species have larger distributions than currently thought.
The undescribed Pohnpeian Tosanoides differs rather remarkably from the two known species in coloration. Its ground coloration is purple and completely unmarked. The nape is embellished with two gold chevrons, and the entire dorsal fin is yellow. The caudal fin is bright purple and an apparent yellow peduncular stripe is present, which runs obliquely to the lower caudal lobe.
Unfortunately, no specimens were collected and the fish is known only from a few in situ photographs and videos. It shares the same habitat and depth range as the first Odontanthias, at 430ft in Ant Atoll, Pohnpei. Its appearance does not resemble the two known Tosanoides in any of their life stages, and very likely represents the genus’ third potential member.
Finally, three stunning new Grammatonotus were collected along side the preceding species. The genus highly resembles Anthiinae in physical form, but are classified in a separate family, Callanthidae. The entire genus is almost wholly restricted to the mesophotic reefs, with very few in situ photographs. The most well known and frequently observed species is the Japanese G. surugaensis, which sometimes occur at 200ft, as well as making the occasional cameo in trawler nets.
The first undescribed species is a gorgeous representation of the genus with a stunning caudal fin. In the in situ photo above, the fish is roughly two-toned, being grape purple anteriorly before suffusing into yellow posteriorly. A closer inspection of the species post mortem reveals a more delicate appearance, with silver edged scales running horizontally along the dorsum. The caudal fin is a remarkable rhombus with a further elongation of the central rays forming two short filamentous extensions.
This unknown phenotype was collected in the same reef as Pseudanthias cf. rubrolineatus, one mile off Palikir Pass, Pohnpei, but at a deeper depth of 450ft.
A second Grammatonotus with a different tail shape was also collected. This specimen shows remarkable variation in its caudal fin, possessing filamentous extensions on the upper and lower lobes instead. When fanned out, this gives the fin a crescentic appearance quite unlike the preceding.
This specimen was collected in the same reef, but deeper still at 497ft.
The final Grammatonotus is a minuscule beauty. At barely two inches long, this species is adorned with numerous vertical stripes set against a yellow ground color. It’s very likely that this specimen is just a juvenile, and it will be curious to see what kind of caudal fin shape develops as it ages.
It was collected from the Southeastern side of Ant Atoll, Pohnpei, at 438ft.
For such a small genus, Grammatonotus is remarkable in possessing such wide variations in its morphology. This is usually more commonly seen in larger genera with multiple species groups, like Pseudanthias and Cirrhilabrus. It’s possible that the revelation of these Grammatonotus phenotypes foreshadows a richer, more complicated phylogeny within the genus with numerous species yet to be discovered. Could the different tail shapes represent distinct clades in the genus? With more deepwater exploration into the mesophotic zones across the Pacific, it’s only a matter of time before these miasmic uncertainties are elucidated.
We leave you with a video taken by Brian in one of his deep dives at Ant Atoll, Pohnpei. Some of the undescribed species we’ve discussed here make their debut in this film. Take note of the largely monotonous habitat made up of deep 45° slopes replete with small caves and ledges. Temperate ranges between a frigid 59-63°F (15-17°C). This depressing habitat seemingly lacklustre in life hides a remarkable cornucopia of colourful fish. Just goes to show that our quest to understand the ocean’s reef has only just begun.
Brian Greene will be speaking at the 2015 MACNA this year in Washington D.C., where he will elaborate more on his expedition processes as well as talk more about deepwater fish. If you’re a fish nerd, you do not want to miss that. So take this as a teaser for better things to come.
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