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MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS?
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Precious corals do not require sunlight and are generally
referred to as deep-sea or cold-water corals. They are found
all over the world, down to the deep ocean depths. However,
the range of precious corals overlaps with MCEs, and in
some areas, such as around Hawai‘i, they can significantly
contribute to habitat complexity and provide stabilization to
substrates at mesophotic depths (Tsounis et al. 2010).
Many of the species used in jewellery manufacture, including
the prized black coral
Antipathes griggi
(Figure 6.13), are
Invasive species are introduced species that are not native to
a particular ecosystem. They may rapidly reproduce, causing
detrimental ecological effects. Several invasive species have
been recorded on MCEs, with the snowflake coral (
Carijoa
riisei
), lionfish (
Pterois volitans
and
P. miles
) and green algae
(
Avrainvillea
sp.) being best documented.
6.7.1.
Snowflake coral
The invasive parasitic snowflake octocoral,
Carijoa riisei,
was
first recorded on the island of O‘ahu in Hawai‘i in the 1960s.
Native to the West Pacific, it is not clear how the snowflake
collected at mesophotic depths. In the past, trawling had
been used to collect the corals (Tsounis et al. 2010). This
practice has now been banned in most countries, limiting
collection to less destructive and more selective harvesting
methods, such as by divers and utilizing submersibles.
Considering the ecological role of precious corals in some
mesophotic habitats, it is important to ensure that harvesting
is sustainably managed to maintain ecosystem functions
(e.g. habitat complexity and substrate stabilisation) provided
by precious corals.
coral was first transported toHawai‘i (Concepcion et al. 2010).
Since its arrival, the snowflake coral has spread around most
of the Main Hawaiian Islands. It settles on black corals and
smothers them (Figure 6.14; Kahng and Grigg 2005). In 2001,
on the Maui Black Coral bed, it was found to cover more than
60 per cent of black corals at depths between 80–105 m and
settle on the undersides of mesophotic scleractinian corals
and overgrow them (Kahng and Grigg 2005). Like many
invasive species, snowflake coral has a high reproductive
rate. It employs continuous spawning of negatively buoyant
eggs, as well as spreading vegetatively using ‘runners’ (Kahng
et al. 2008).
6.6.
Precious coral fishery
6.7.
Invasive species
Figure 6.13.
Black corals (Antipatharia) frommesophotic depths (70–100 m) in the
‘
Au
‘
au Channel, Hawai
‘
i located between the islands
of Lāna
‘
i and Maui (photos NOAA’s Hawai
‘
i Undersea Research Laboratory).
Figure 6.14.
The
‘
Au
‘
au Channel, Hawai
‘
i at 70–100 m showing (a) the snowflake coral,
Carijoa riisei
, smothering a black coral colony and
(b) a
C. riisei
dominated mesophotic habitat (photos NOAA’s Hawai
‘
i Undersea Research Laboratory).
(a)
(a)
(b)
(b)