Soft-Bottom Subtidal Ecosystems (0-100 meters)

 

A DECEPTIVELY COMPLEX ECOSYSTEM

For MPA monitoring, soft-bottom subtidal ecosystems encompass the areas of sediment substrate occurring at depths between mean lower low water and 100 meters. These habitats are much more common than rocky habitats at all depth zones throughout the California coast. Although these habitats are seemingly simple and unstructured, they are rather dynamic, and inhabitant species must contend with dramatic changes as waves and currents shift sand and sediment across large areas.

 

A HOME IN DEEP GROVES

Adding to the complexity of these habitats, some areas feature rippled scour depressions (RSDs), or deposits of coarse-grained sediments that are depressed below the surrounding sediment that form important habitat for fish and invertebrates. Brittle stars and sea stars are common in this habitat, as well as commercially important species such as Dungeness crab, sand dabs, and starry flounder.

 

UNDERSTANDING TRENDS INSIDE AND OUTSIDE MPAS

Many of the fish and invertebrate species in soft-bottom subtidal ecosystems are wide-ranging, and individuals are likely to move between protected and unprotected locations. Detecting the effects of MPA designation on these species is challenging, but insights can be garnered by combining ecological data with information about the spatial patterns of fishing occurring outside of MPAs.

Decadal-scale shifts in the California Current can also result in warm and cool regimes that affect the sediment-inhabiting communities in this ecosystem. When warm regimes occur, declines in plankton production are likely – resulting in species and community declines as well. On shorter timescales, El Niño events, which increase wave activity and storms (leading to sedimentation), can cause major short-term disturbances to these ecosystems. As a result, integrated analyses of trend data are needed to separate MPA effects from other anthropogenic and natural system drivers.