The nearshore zone extends from the surf out to waters that are approximately 30 meters (100 feet) deep. Waves and currents interact with the sandy seafloor in this relatively shallow zone, creating sand waves and ripples and organizing sediment particles into different group sizes.
The lack of hard substrate and the shifting sand prevent algae from settling, therefore these vast sandy plains stretching in all directions appear to be lifeless deserts. However, looks can be deceiving.
Many organisms make their homes either on (i.e., epifaunal) or in (i.e., infaunal) the sediments.
In particular, two communities are organized along a gradient of wave-induced substrate motion:
- The crustacean zone: this shallower zone, characterized by strong water motion and sandy sediments, is occupied by small, mobile, deposit-feeding crustaceans.
- The polychaete zone: characterized by more stable, fine sand with a significant amount of mud, this deeper zone is dominated by polychaete worms living in relatively permanent tubes and burrows. Many other relatively sessile and suspension-feeding groups are also common here.
The width and depth limits of these two zones vary, depending on the strength of wave activity.
Benthic fishes are less abundant in the crustacean zone than the polychaete zone. Fish diversity on the sandy seafloor is relatively low compared to adjacent reefs, but some of the most abundant species are important forage for large predatory fishes, seabirds and marine mammals.
The most common natural disturbance in the sandy seafloor habitat is from wave action. Other disturbances are biotic – such as from the digging activities of feeding southern sea otters, Enhydra lutris.
Within the three northern California sanctuaries, monitoring efforts focused on the sandy floor are currently underway only in the Monterey Bay sanctuary.
Examples of related monitoring projects: