Mesophotic Coral Ecosystems

6.6. Precious coral fishery

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

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.

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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).

6.7. Invasive species

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

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).

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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).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 78