Marine Atlas: Maximizing Benefits for Vanuatu

HOW MUCH DO WE REALLY KNOW? COLD-WATER CORAL HABITATS While quite a lot is known about Vanuatu’s inshore environment, some habitats are hard to explore and map. For example, although cold-water corals can be common and important deep-sea species, little is known about their dis- tribution and abundance in Vanuatu’s waters. Their sensitivity to human impact and future climate change should be considered when assessing management options for deep-sea ecosystem conservation.

deep-sea fishing. They are fully protected in some countries (e.g. New Zealand).

The Moon or the sea?

Corals are not restricted to shallow-water tropical seas. Deepwater or cold-water corals are regarded as occurring deeper than 50 metres, and 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 Octocorallia (soft corals, gorgoni- ans, bamboo corals), and family Stylasteridae (lace corals) (Roberts et al., 2009). They are widespread throughout the Pacific Ocean. At present, cold-water corals have no economic importance for Vanuatu. However, many of them have been recognized as playing important eco- logical 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 asso- ciated invertebrate and fish species. 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 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 Vanuatu’s waters un- doubtedly hold a lot of secrets, including deep- water or cold-water corals. These corals have a

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. 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- 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

The map shows the predicted suitability of habitat where octocoral species could occur. Octocorals are a highly diverse group, with soft corals, gorgo- nians, sea fans, sea whips, sea feathers, precious corals, pink coral, red coral, golden corals, bamboo corals, leather corals, horny corals, and sea pens among their estimated 2,000-plus species (Roberts et al., 2009). Globally accessible data for offshore corals are sparse in many Pacific Islands, including Vanuatu. In fact, data available through the Ocean Biogeographic Information System (OBIS) in 2015 supplemented with New Zealand regional records (NIWA) show only 15 records of cold-water octo- corals in Vanuatu’s waters (mainly primnoid corals and soft corals). This has led to the need for habitat suitability modelling to be used to predict the likely occurrence of corals in the area. Habitat suitability was highest along the major ba- thymetric features in the EEZ, with high predicted occurrence in a nearly continuous band along the main island ridge and island slopes, as well as on the West Torres Plateau west of the Torres Islands and bordering the Torres Trench. The distribution largely follows depth, with topography also a fac- tor. These ridge and bank features are shallower than many of the abyssal plains in the EEZ, with higher food availability. The steep topography pro- vides hard rocky substrate which the corals need for attachment. Although not presented, similar analyses have been carried out for five species of stony coral (order Scle- ractinia) (Davies and Guinotte, 2011). Depth, tem- perature, aragonite saturation state and salinity were the key environmental drivers for this taxonomic grouping. The published figures do not indicate high suitability for these corals around Vanuatu. Habitat suitability modelling examines the relation- ship between where the corals are known to occur and key environmental conditions at that location. This relationship enables extrapolation into areas that have not been sampled, based on the suitabil- ity of 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). The presence of cold-water corals can be an important indicator for managing human activities to avoid or minimize impacts on deep-sea ecosys- tems. The habitat suitability map, although based on presence-absence rather than abundance, gives an indication of which areas may need protection from disturbance of the sea floor or climate change.

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




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