Black Corals, Antipatharia, are
Anthozoan Hexacorallid Corals known from across the world’s oceans,
particularly in waters below the photic zone, waters shallower than about 50 m
where light levels are high and attached benthic communities are dominated by
photosynthetic organisms, such as Macroalgae (Seaweeds) and Coral species which
host symbiotic single-celled Algae, and have been recorded at depths below 8600
m in the Western Pacific. All Black Corals are colonial, they have largely
proteinaceous skeletons with minute spines, mouths surrounded by eight
non-retractable tentacles and stomachs with eight mesentery canals
(single-ended digestive canals which much be emptied of waste matter by periodic
eversion). Because most Black Corals live at depths where surveys by Scuba
divers are impossible, very little is known about their distributions, with
most species known only from single records, though in some areas where
shallow-water Black Corals occur better records exist.
One area where such shallow-water
Black Corals are abundant is the Hawaiian Archipelago. Here Black Corals are of
some economic significance, having been used in traditional Hawaiian medicine,
and with a commercial harvesting industry which collects Black Corals for the
jewellery industry (Black Coral is the official State Gemstone of Hawaii). As
such a large number of surveys of Black Corals at shallow depths have been
carried out in Hawaii, although these are generally local in nature and
concentrated around the inhabited islands in the southeast of the archipelago.
In a paper published in the
journal Marine Biodiversity Records on 17 April 2015, Daniel Wagner of the NOAA’s Papahānaumokuākea Marine National Monument publishes an analysis of the distribution of
shallow-water Black Coral species from the Hawaiian Archipelago, based upon
collected surveys from the harvesting industry, collection records from museum
specimens, and photographic and video records from submersible surveys carried
out by the Hawai‘i Undersea Research Laboratory and Monterrey Bay Aquarium Research Institute as well as published records in scientific literature.
For the purpose of this study
‘shallow-water’ was defined as less than 150 m from the surface, the base of
the mesophotic zone (the zone below the photic zone where photosynthesis is not
carried out but the water is not in permanent darkness) in the clear waters of
Hawaii. A total of eight species of Black Corals were recorded, though since
the surveying was somewhat patchy in the northern part of the islands this
cannot be concluded to be an exhaustive list of the species present. All
species grow attached to hard substrates and favour areas of high currents; it
is likely that the current affects the distribution of these Corals, but
sufficient records were not available to include this in the survey.
The first species recorded is Antipathes griggi, a commercially
significant species found throughout the islands from Hawai‘i to Pearl and
Hermes Atoll at depths of between nine and 110 m, but most abundant between
forty and fifty meters and fairly rare below sixty meters. The species was
found to tolerate temperatures of 22.30-27.41˚C, and has a dense bushy crown
which extends into the current flow.
(Left) Growing specimen of Antipathes
griggi. (Right) The known distribution of the species within the Hawaiian
Archipelago. Wagner (2015).
The second species recorded is Antipathes grandis, another commercially
important species which is found from from Hawai‘i to Ni‘ihau at depths of
depths of between 24 and 146 m, but which is most abundant between 90 and 110
m, and fairly uncommon shallower than 50 m or deeper than 120 m. This species
also has a dense bushy crown, and lives at temperatures of 20.01-26.91˚C.
(Left) Growing specimen of Antipathes
grandis. (Right) The known distribution of the species within the Hawaiian
Archipelago. Wagner (2015).
The third species recorded is Cirrhipathes cf. anguina (i.e. probably Cirrhipathes
anguina a specimen cannot actually be
confirmed as belonging to a species without comparing it to the holotype –
first specimen described – which with some older species, such as Cirrhipathes anguina which was described in 1846, is not always possible) which
is found from across the archipelago from Hawai‘i to the north-west of Brooks
Banks at depths of between nine and 150 m, although it is less common below 60
m. Cirrhipathes cf. anguina is a wire Coral (i.e. its
colonies consist of a single wire-like strand) found at temperatures of
21.92-27.69˚C.
(Left) Growing colonies of Antipathes
grandis. (Right) The known distribution of the species within the Hawaiian
Archipelago. Wagner (2015).
The fourth species recorded is Stichopathes echinulata, which is found
across the archipelago from Hawai‘i to Lisianski, at recorded depths of 90-150
m, and probably also deeper than it was possible to evaluate using the records
available for this study. Stichopathes
echinulata forms unbranching wire-shaped colonies and lives at temperatures
of 19.59-22.91˚C.
(Left) Growing colony of Stichopathes
echinulata being manipulated by the arm of a submersible. (Right) The known
distribution of the species within the Hawaiian Archipelago. Wagner (2015).
The fifth Coral species recorded
is Stichopathes? sp. (an unidentified
species of Coral which probably belongs to the genus Stichopathes) which was found from Hawai‘i to French Frigate Shoals
at depths of 9-58 m, though it was never abundant. This species also forms unbranching
wire colonies, though insufficient data was available to determine its
temperature preferences.
(Left) Growing colonies of Stichopathes?
sp. (Right) The known distribution of the species within the Hawaiian
Archipelago. Wagner (2015).
The sixth Coral species recorded
is Aphanipathes verticillata, which
has been found only in the Keyhole Pinnacle area of the Au‘au Channel, at
depths of 88-130 m. This species forms flat branching colonies and is found at
a temperature range of 19.88-22.96˚C. The Hawaiian population of Aphanipathes verticillata was only
discovered in 2008, and is thought to be a distinct subspecies, Aphanipathes verticillata mauiensis,
though it closely resembles the related Antipathes
griggi, and cannot be differentiated without close examination of the
polyps, making it likely that many older surveys have failed to identify this
species, and that it is more widely distributed within the Hawaiian Archipelago
than is currently appreciated. Other populations of Aphanipathes verticillata are known from Mauritius and Okinawa,
which supports the idea of this species being more widely distributed.
(Left) Growing colonies of Aphanipathes
verticillata mauiensis. (Right) The known distribution of the species
within the Hawaiian Archipelago. Wagner (2015).
The seventh species of Coral
recorded is Acanthopathes undulata,
which is found across the archipelago from Hawai‘i to Laysan at depths of
32-150 m, although it is more common below 100 m. Acanthopathes undulata forms branching colonies. It was not
possible to establish a range of temperature preferences for this study.
(Left) Growing colonies of Acanthopathes
undulata. (Right) The known distribution of the species within the Hawaiian
Archipelago. Wagner (2015).
The final species recorded was Myriopathes cf. ulex, which is a commercially exploited species found across the
archipelago from 30-150 m; it is more commonly recorded at depths of 60 m or
shallower, though this may reflect the limit of harvesting potential rather
than the true distribution of colonies, and the species may also be present
deeper than 150 m, the limit of the survey. Myriopathes
cf. ulex forms densely branching
fan-shaped colonies, and has a temperature range of 20.52-26.99˚C.
(Left) Growing colonies of Myriopathes
cf. ulex. (Right) The known
distribution of the species within the Hawaiian Archipelago. Wagner (2015).
All of the Coral species examined
in this study had depth and temperature ranges which overlapped with other
species. Nevertheless there was clear separation in the habitat preferences of
these species, particularly in mean temperature (the average temperature at
which colonies were found), with Antipathes
griggi colonies found in waters with an average temperature of 26.25˚C, Cirrhipathes cf. anguina having a mean temperature of 26.27˚C, Antipathes grandis 24.25˚C, Myriopathes
cf. ulex 22.56˚C, Aphanipathes verticillata 21.19˚C and Stichopathes echinulata 21.08 ˚C.
Furthermore, where species pairs had close mean temperature preferences, such
as Antipathes griggi and Cirrhipathes cf. anguina or Aphanipathes
verticillata and Stichopathes
echinulata, they quite often had very different polyp sizes, suggesting
that they were exploiting different resources. It is very likely that the
distribution of these Corals is affected by other factors, such as current
speeds and food supply (i.e. the amount of edible food in the water passing
over them), but these were beyond the scope of the current study.
See also…
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