(Photo courtesy of Richardson Bay Marina)

Richardson Bay, the inlet that opens into the San Francisco Bay from Sausalito and Tiburon, is home to multiple fragile ocean ecosystems that depend on eelgrass as a habitat, nursery, and food source.

According to a new study by Audubon California, the illegal mooring of private boats has caused significant harm to the eelgrass bed in that bay, with 25 to 41 percent of the seafloor habitat suffering damage.

The number of boats moored in Richardson Bay, known as “anchor-outs,” has increased from about 90 boats in the early 2000s to as many as 240 in 2016. The boats’ anchors, tackle and other equipment can tear up the eelgrass, causing round areas of damage that resemble “crop circles” as the boats move with the tide. Environmental damage also occurs in the form of oil and gas leaks, improper waste disposal and crowding of the surface that drives away sea birds.

Eelgrass is an essential food source for the black brant, the surf scoter and other water birds, provides a habitat for Pacific herring and supports an intricate web of aquatic species, as well as beautifying the waters. Eelgrass beds have been extensively damaged throughout the San Francisco Bay by dredging, coastal development, fishing and climate change, according to an Audubon California study released May 17.

Audubon California puts the eelgrass losses in San Francisco Bay at 900 acres, or 25 percent of the total eelgrass beds, over a five-year period between 2009 and 2014. Richardson Bay has fared even worse.

Proposed solutions include moving the boats, building fixed mooring emplacements, and implementing stricter regulations. But the mounting threats to the eelgrass beds, and, more broadly, to the San Francisco Bay’s intricate and fragile ecosystems, will continue.