Marine Atlas: Maximizing Benefits for Fiji

HOW MUCH DO WE REALLY KNOW? COLD-WATER CORAL HABITATS While quite a lot is known about Fiji’s inshore environment, some habitats are hard to explore and map, especially those found deep below the surface where conducting research is both expensive and complicated. To map Fiji’s important cold-water coral communities, scientists use habitat suitability models that guide us to where they are likely to be found.

because actual species records are sparse. Data available through the Ocean Biogeographic Infor- mation System supplemented with New Zealand regional records (NIWA) show only 19 records of cold-water octocorals, comprising nine species, in Fiji’s waters. The relationship between where the corals are known to occur and key environmental conditions in these locations has been used in these models to extrapolate into areas that have not been sampled, based on a range of globally recognized environmental factors. For octocorals, temperature, salinity, slope of the sea floor, ocean productivity, dissolved oxygen levels, and calcite saturation state were important factors controlling habitat suitability (Yesson et al., 2012). Habitat suitability was highest along the major bathymetric features in Fiji’s waters, with high predicted occurrence continuously along the Lau Ridge (running north–south), the Moore and Den- ham Ridges to the south-west and Charlotte, Alexa, Louisa and Morton Banks in the north. These ridge and bank features are shallower than much of the abyssal plains in Fiji’s waters (with greater food supply by the sea floor), and have higher slopes associated with steep topography. The latter is also associated with a greater amount of hard rocky substrate, which the corals need for attachment. Although not presented in a figure, similar analyses have been carried out for five species of stony cor- al (order Scleractinia) (Davies and Guinotte, 2011). Depth, temperature, aragonite saturation state and salinity were the key environmental drivers for this taxonomic grouping (see also chapter “Go with the flow”). The published figures do not show the area north of the main islands of Fiji, but predict high suitability for at least one of the species (Enal- lopsammia rostrata) along the Lau Ridge, similar to the octocorals.

The Moon or the sea?

Cold-water corals include five taxa and over 3,300 more species than their better known tropical coral reef counterparts: order Scleractinia (hard, stony corals), order Zoanthidea (zoanthids, gold corals), order Antipatharia (black corals), subclass Octo- corallia (soft corals, gorgonians, bamboo corals), and family Stylasteridae (lace corals) (Roberts et al., 2009). Many of these corals have been recognized as play- ing important ecological roles in the deep sea, since they can form large reef-like structures or have complex growth forms which in turn provide habitat for many associated invertebrate and fish species. Cold-water corals are widely regarded as being susceptible to damage from human activities, such as direct effects from fishing, deep-sea mining and submarine communication cables (see also chap- ters “Fishing in the dark” and “Underwater Wild West”), as well as more indirect impacts from pol- resolution of around 5 kilometres, unveiling most features larger than 5 kilometres across (Sandwell, 2014). However, only 0.05 per cent of the ocean floor has been mapped to a high level of detail, meaning Fiji’s waters undoubt- edly hold a lot of secrets, including deepwater or cold-water corals. These corals have a There is a common misconception that we know more about the surface of the Moon than the ocean floor and that 95 per cent of the ocean is unexplored. The chapter “Voyage to the bottom of the sea” showed that we actually know a lot about the ocean floor. The entire ocean floor has been mapped to a maximum

depth range extending from around 50 metres to beyond 2,000 metres deep, where water temperatures may be as cold as 4°C (see also chapter “Still waters run deep”). While there are nearly as many species of cold-water corals as shallow-water corals, only a few cold-water species develop into traditional reefs. This is also why they are much harder to discover and map than their shallow-water counterparts. Nevertheless, scientists have created habitat suitability models that use information on the physical environment to predict their distri- bution and provide an understanding of their ecological requirements. lution and climate change (see also chapters “The dose makes the poison” and “Turning sour”). Many species of cold-water coral are structurally fragile, and hence easily broken. They can also be long- lived and slow-growing, meaning that any recovery from damage is slow. Therefore, the presence of cold-water corals can be an important indicator of the need to manage human activities to avoid or minimize impacts on these deep-sea ecosystems. For instance, octocorals are one of the groups that FAO lists as potentially Vulnerable Marine Ecosys- tems (FAO, 2009), and which are required under United Nations resolutions to be protected from deep-sea fishing. They are fully protected in some countries (e.g. New Zealand). The map shows the predicted suitability of habitat where octocoral species could occur. Octocorals are an important group because they are known to be very widespread throughout the Pacific Ocean. Habitat suitability modelling has been used

The bamboo coral Keratoisis grandiflora, which has been recorded in Fiji’s waters.




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