Submarine canyon ecosystems

Deep-sea submarine canyons are deep incisions of the continental shelf and slope, dissecting much of the European ocean margin. Were these canyons on land, they would present some of the most dramatic mountain scenery in the world but hidden by the ocean, and covered in a drape of sediment, they have been largely ignored until now because of the difficulties in exploring their complex terrain. Advances in technology such as ROVs, swath bathymetry, sidescan sonar, and the extensive use of long term instrumented moorings, are allowing new insights into these challenging environments.

While some canyons are closely connected to major river outflow systems, others channel large quantities of sediment from the continental shelf into deep water. Past research has shown that canyons act as major pathways for transport of organic carbon, anthropogenic substances and urban waste to the deep sea, but the sites of final deposition remain largely unknown. It is also unclear whether some canyons act as sediment traps rather than conduits.

Episodic flushing events carry large amounts of sediment to the deep sea but the frequency and amplitude of these events are poorly understood, as are the effects on benthic biodiversity and ecosystem functioning. Recent studies of a canyon in the NW Mediterranean highlighted the link between Dense Shelf Water Cascading (DSWC), a climate-related phenomenon, to long-term fluctuations in a deep-sea shrimp fishery.    

whittard_anemones

The importance of canyons as refugia for aggregation and spawning and for larval sources/sinks for other margin ecosystems is still unknown and the degree of endemism within canyons remains unexplored.  The roles of seabed heterogeneity, food quality and supply, hydrodynamics and hydrography in relation to distribution of deep-sea taxa are still to be explored.

Left: Anemones cling to a boulder in the Whittard Canyon, Celtic margin. Image courtesy NOCS/JC36.

Canyons are complex systems in terms of hydrography, sedimentology, biogeochemistry and biology and great variability occurs both within individual canyon systems and between different canyons. Individual canyons have very different environmental characteristics that determine the diversity and the ecology of their fauna. To devise policies appropriate for whole ecosystem management an improved understanding of these complex systems is essential, particularly as canyons are being considered as potential disposal sites for various wastes, including carbon dioxide. HERMIONE studied canyon systems in six different biogeochemical provinces, using multidisciplinary teams to investigate the ecological significance of canyons by looking at relationships between biodiversity, ecosystem function and services.   

HERMIONE Canyon expeditions:  
JC36 Exploring the geology & biology of the Whittard Canyon (RRS James Cook, June-July 2009)


1/9: Submarine canyons

Nazaré Canyon is the largest submarine canyon in Europe and also one of the most active in terms of current regime, sediment transport and sediment deposition.

2/9: Life on the edge

The topography in the canyon is very complex and changes over small distances – just 100 metres can make the difference between life on a calm, flat terrace, or life literally on a cliff edge!

3/9: Food, glorious food!

Animals that trap food particles from the water currents flowing past them are known as filter-feeders. They prefer the fast-flowing, nutrient-rich waters near the central axis of the canyon.

4/9: Peace and quiet on the terraces

Others animals, like these sea cucumbers feed on organic material in sediments, and prefer to live on flat terraces of the canyon where the calmer environment allows nutrient-rich sediment to be deposited.

5/9: A slippery slope...

Steep slopes and cliffs in the canyons typically attract more filter feeders, and here in the upper canyon you will typically see corals, sponges and the enigmatic xenophyophores.

6/9: Survival of the fittest

If currents are very strong, a lot of sediment is carried in the water making it very turbid. These conditions are often found in the upper reaches of the canyon where topography is very uneven and rugged.

7/9: Diverse habitats

The habitats in canyons can change dramatically over a small spatial scale, and the animals that inhabit them change just as quickly. Compared to other areas, canyons can have much higher species diversity.

8/9: Canyons increase margin diversity

The continental margins of the whole world are littered with submarine canyons. Submarine canyons probably contribute heavily to maintaining high species diversity across the world’s margins.

9/9: Trashy habits

Speaking of littering...from fishing gear to bottles and plastic bags, Nazaré Canyon has been funnelling discarded items from the shelf to the deep sea – an example of how humans impact our oceans.

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