Another name for the bottom of the Bay is the benthic habitat. Scientists have been measuring the effects of pollution on the plants and animals of the benthic habitat, particularly near the sewage outfalls from the City of Los Angeles' Hyperion Wastewater Treatment Plant (Hyperion) and the Los Angeles County Sanitation District's Joint Water Pollution Control Plant (JWPCP), since the early 1950s. Benthic organisms are considered good indicators of environmental health because they are not as mobile as fish and they live in the sediments where contaminant concentrations are generally the highest.
Most of the Santa Monica Bay sea floor consists of soft sediments, which are a mixture of sand, silt and clay. This subtidal, soft-bottom habitat supports a diverse number of organisms, including more than 100 species of bottom-dwelling (demersal) fish. Major members of the fish community in the Bay's shallow soft-bottom regions include white croaker, queenfish, surfperches, California halibut and barred sandbass.
Through the 1970s, the Bay's benthic habitat appeared more changed and degraded the closer one measured to the sewage outfall discharge areas. This meant that these areas of Bay bottom supported far fewer numbers and types of species of plants and animals; in short, the environment was unhealthy and lacked diversity.
Today, the ocean floor areas affected directly by wastewater outfalls have become significantly smaller. Although the effects of the wastewater on surrounding fish and invertebrate communities are still noticeable, environmental monitoring programs show that marine life communities near outfalls are beginning to resemble those in more pristine areas.
Tumors, fin erosion and other diseases-at one time common-are now only rarely observed in demersal fish such as Dover sole. Sensitive species are returning to areas from which they were long absent. Even the severely degraded environment around the now-closed Hyperion seven-mile sludge pipe is slowly recovering, as evidenced by declining contaminant concentrations in sediments and increased species diversity.
The benthic environment can also be affected by trash and debris that sink to the bottom of the Bay. One particular section of the Bay floor, to the north of Hyperion's seven-mile outfall, has a reef of old beer and soda cans at a depth of about 175 feet, refuse dumped for decades by fishermen and pleasure boaters.