Rocky reefs are submerged rock outcrops with varying relief, creating refuges for juvenile and smaller fish in addition to surface area for colonization of algae and invertebrates. Rocky reefs take a variety of forms, each with a different associated biological community. Starting from the shore, rocky intertidal zones are an interface between land and sea. The rocky intertidal is home to plants, invertebrates, and fish during high tides. Crashing waves, daily low tides that strand marine organisms out of the water, and competition for space make life in the rocky intertidal stressful. Nearshore rocky reefs are completely submerged, but still receive enough light for photosynthesis. They are inhabited by algae, invertebrates, and groundfish.
Rocky reefs in deeper water do not receive enough light for photosynthesis and are dominated by sessile invertebrates, deep sea corals, and groundfish. Most rocky reefs are beneficial because of the physical structure they provide to support an ecosystem. Seamounts are particularly unique habitats that are formed by undersea mountains. The steep slopes of the mount force nutrient rich deep waters to rise to the surface, generating food for a variety of fish and other marine fauna.
Along the West Coast, the Pacific Fishery Management Council identified rocky reefs as a Habitat Areas of Particular Concern (HAPC).
Many species of groundfish inhabit rocky reefs because they can find shelter from predators. In reefs close to the surface, algae can attach to the rocks and provide the base of a food chain, making rocky reefs highly productive. When reefs exist at depth below where sunlight can penetrate, invertebrate filter feeders dominate the community, capturing prey as they pass by in the current. Deep sea corals also form on these reefs. These corals grow very slowly and can live for hundreds of years. Some reefs exist in the intertidal area where they are only submerged a portion of the time. This stressful habitat leads to a diverse assemblage of plants and animals that are adapted to life in and out of seawater.
Seamounts are submerged mountains that create islands of productivity in relatively nutrient-poor open ocean habitats. Deep ocean currents collide with the seamount, forcing nutrient-rich deep waters to the surface. The nutrient upwelling supports aggregations of pelagic and highly migratory fish such as billfish and sharks as well as many species of marine mammals, including whales.
Rocky reef habitats provide many benefits to society known as ecosystem services. Corals that form on deep rocky reefs can live for hundreds of years. Because of their longevity, scientists can examine their skeletons for evidence of long term climate change. Some deep sea corals are being researched for their pharmaceutical applications to cancer and heart disease drugs. Similarly, keyhole limpet, often found on rocky reefs, have proteins in their blood used in cancer drugs.
The diverse fish and invertebrate assemblages attract divers to witness not only the beauty of this habitat, but also to pursue abalone and lobster. Recreational fisherman know that groundfish such as lingcod, many species of rockfish, and cabezon prefer rocky reefs and take advantage of this knowledge when searching for prime fishing locations. Commercial fisherman take groundfish that may have matured on reefs or coastal pelagic and highly migratory species that benefit from reefs for shelter and/or prey.
Bottom trawls (fishing gear that scours the substrate) are the primary threat to rocky reef habitats. The shelter that makes rocky reefs desirable habitat is eliminated when trawls demolish the reef structure. Deep sea corals that took hundreds of years to grow can be destroyed in a very short time. If fishing gear is caught on the reef, it can continue collecting and killing animals for many years in a process known as ghost fishing. While most harvesting techniques are not destructive to the reef, removing too many individuals from a species can shift ecosystem structure, potentially making the system less productive. Visitors to rocky intertidal habitats located near urban centers frequently trample, remove, and disturb the biological community.
Increased sea temperatures and ocean acidification from global warming will make it possible for many colonial invertebrates to secrete their skeletons. Without these invertebrates, the rocky reef habitat will lose a major source of productivity and important link in their food web.