Off the coast of Southern California between Point Conception and Cabo Colnet, about 250 km south of the border in Baja California, lies an area of ocean floor that is very unusual compared to seafloor anywhere else in the world. The geological origin of this area is not well understood, but in geological terms it is referred to as a continental borderland.
The area, generally called the Southern California Bight, covers about 30,115 square miles (78,000 km2), spans a northwest to southeast distance of about 621 miles (1000 km), and is about 186 miles (300 km) at its widest. It is unique because of the extensive system of subsea ridges, banks, and basins that it contains. In some places the ridges are tall enough to break the ocean surface, and form the various islands found in the area. The basins range in depth from about 1,970 feet (600 m) to over 9,800 feet (3000 m). The large range of ocean depths, and the influence of ocean currents from both the north and the south, results in a high diversity of marine species, which also adds to its uniqueness.
I took today’s photo while diving on one of the more accessible banks found in the area. Located about 5 miles (8 km) south of Catalina Head on Santa Catalina Island, Farnsworth Bank is a small shallow area that comes to within about 55 feet (17 m) of the surface, but the bottom is at least at 200 feet (60 m). Even though this bank is part of the bank that is Santa Catalina Island, like other banks and ridges in the larger area, it is bathed by clear open ocean currents.
Off greatest note are the purple finger-like structures know as purple hydrocorals (Stylaster californicus), which are found in very few places along the coast and are protected by a marine preserve that surrounds the area. On some parts of Farnsworth Bank, you can’t see the rocky bottom for the nearly continuous blank of purple hydrocorals attached to it.
In addition to the hydrocorals, fish are another big component of a dive at Farnsworth. Because of the protection of reef fish by the reserve, many species have grown prolifically here. In the photo you can see the dense school of blacksmith fish (Chromis punctipinnis) in the water above the reef. These plankton-eaters swim in large aggregations facing into the prevailing current eating microscopic animals that sweep past the reef.
Farnsworth Bank is a small portion of the Southern California Bight, but it representative of the abundance of marine life that can be found within this continental borderland.
Today's photo was made with a Canon 8-15 mm f/4L fisheye lens zoomed to 15 mm on a Canon 5D Mk. III in an Ikelite underwater housing. The scene was illuminated with two Ikelite DS-161 strobes in eTTL mode. The exposure was set to 1/30 sec. at f/8 and ISO 100.