Introduction

The deep-ocean floor (>1000m) covers 60-62% of the Earth’s surface (Glover & Smith 2003, Davies et al. 2007). It is the last major wilderness area on the planet (Roberts 2002) and is dominated by abyssal plains; this is due mainly to the fact that almost all of the biomass produced in surface waters is recycled during the sinking process, so only a small fraction of food reaches the ground to sustain any life. Though it is not all doom and gloom, some oases do exist in the deep desert. There are Hydrothermal Vents, Cold Seeps and there are also cold-water coral (CWC) reefs.

Coral reefs are widely acknowledged as being some of the most spectacular ecosystems on Earth (Figure 1). A great deal is known about corals situated in well-lit, shallow tropical seas where the polyps are packed with symbiotic algae (zooxanthellae); these provide them with energy and the ability to develop their calcareous skeletons (Freiwald et al. 2004).

Picture demonstrating the beauty and diversity of cold water corals.

Fig.1. An example of a cold-water coral reef 850m deep off the coast of Ireland (Freiwald et al. 2004).

Lesser researched are their cold-water cousins. Although their existence has been known for centuries, as far back as the 18th (Roberts et al. 2006), they have only been observed and studied extensively in their natural surroundings during the past decade (Freiwald et al. 2004). This has coincided with advances in technology, such as robotic submersibles and advanced acoustic surveying techniques. These methods have helped reveal the scale and abundance of cold-water coral ecosystems (Roberts et al. 2005).

CWC ecosystems can be found in almost all of the world’s oceans seas; they occupy fjords, continental shelves and sea-mounts (Freiwald et al. 2004). They can grow as isolated colonies or they can form large reefs over thousands or even millions of years. Living without light in nutrient-rich waters they are forced to adapt to a different lifestyle.

This review aims to summarise what we know, and the importance of these ecosystems, highlighting aspects of their ecology, distribution and importance for conservation, major threats and the gaps in current scientific knowledge.

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