Physically, they are complex, with outcrops, steep slopes, and different classes of substrates. They also provide a high flux of fine-particle nutrients and often encompass areas of upwelling, which are associated with high biological productivity. While much of the canyon bottom is sand, the hard substrate exposed at the heads of canyons and along canyon walls provides habitat for sessile species of sponges, corals, and anemones, which require a hard surface on which to attach. Because the incidence of these populations is restricted by the availability of hard substrate, and because canyons frequently provide the only such features within a wide area, disruptions to canyon environments could significantly impact these species. Some deepwater coral species have exceptionally slow growth rates and do not recover easily from disruptions.
Canyons also provide a refuge for juveniles of commercially important fish and crabs.
The heterogeneous habitat provided by hard substrate outcrops and the sessile organisms inhabiting them offer refuge from predators for both juveniles and adults. During the NRDC workshop, Hudson Canyon was cited by several participants as a priority area for protection. Besides being a dynamic environment supporting nurseries for a variety of fish and crustaceans, the head of Hudson Canyon is home to tilefish burrows, which in turn attract secondary burrowing and support a highly diverse community. Norfolk Canyon is noteworthy because it contains what is possibly the southernmost outpost of fauna associated with boreal red coral. This canyon was nominated in 1975 as a marine sanctuary, but was never designated as such.