The Port of San Diego continued a state of emergency this month as officials battle an invasive algae species that threatens to damage sea life in San Diego Bay.
The algae, scientifically known as Caulerpa prolifera, is native to Florida and other subtropical locales. It was first discovered in the Coronado Cays in late September during a routine water survey prior to the replacement of an existing dock. After divers identified the Caulerpa, follow-up surveys revealed other patches of the algae within the Cays.
Then, in mid April, divers found more Caulerpa patches in the San Diego Bay National Wildlife Refuge, adjacent to the Coronado Cays.
Since the initial discovery, patches totaling nearly 11,200 square feet have been located. That’s about a quarter of an acre.
“Caulerpa is extremely invasive,” said Eileen Maher, director of environmental conservation for the Port of San Diego. “It reproduces asexually and it grows very quickly, so it can take over native habitats extremely fast if it’s not kept in check.”
Algae poses threat to marine life
The concern arises from the algae’s tendency to choke out native seaweeds and seagrasses, potentially harming marine life due to a loss of habitat and food.
Port officials are focused on protecting the nearly 2,600 acres of eelgrass in San Diego – 1,900 of which are in the South Bay – from the Caulerpa outbreak. Eelgrass plays an essential role in the ocean’s ecosystem as it provides fish, birds and green sea turtles with food and shelter. Simultaneously, it works as a natural water filter and carbon sequester – ultimately improving water and air quality in the region.
It is suspected that the algae made its way into the water due to someone dumping an aquarium either directly into the bay or into a gutter that led to the bay. While it is a popular seaweed in saltwater aquariums, Caulerpa prolifera is illegal to possess, sell or transport in California due to its environmental risks. The ban was signed into law last year after an outbreak in Orange County waters.
Officials battle the outbreak
In San Diego Bay, divers so far have contained the patches of Caulerpa with weighted, sealed barriers to kill off the algae by blocking it from light, oxygen and tidal circulation – preventing it from conducting photosynthesis.
The Port of San Diego has been working alongside the City of Coronado and the Cays homeowners association, as well as federal, state and other local agencies. So far, around $900,000 dollars has been contributed toward fixing this ongoing issue, with an additional $2.2 million in funding pending from federal and state sources, as well as up to $500,000 included in the Port District’s preliminary budget for 2025.
In a minimum of six months, the Port of San Diego will reassess the barriered patches to see if the algae has been killed. After Caulerpa has been eradicated, divers will conduct quarterly monitoring for two years to ensure that there are no new infestations. If no new patches are discovered, then the San Diego Bay will be considered clear of Caulerpa.
This is the first time in San Diego history that Caulerpa prolifera has been discovered in the bay, although it has been found in other regions of Southern California. In the early 2000s, a species of Caulerpa infested part of Huntington Harbour and Aqua Hedionda Lagoon in Carlsbad. More recently, Newport Bay discovered an infestation in 2021. Authorities there are still battling that outbreak.
San Diegans encouraged to avoid Caulerpa
The algae reproduces by a process known as fragmentation whereby pieces literally break off and grow. Because of that, the Port District has asked kayakers, swimmers, divers and boaters to avoid infested areas, or gently transit them at high tide. While the species is not harmful to people, it is a precaution to avoid further spreading the algae.
Rich Grunow, the director of community development for Coronado, also urged city residents not to dump contents of aquariums into the bay or ocean.
Additionally, The Port of San Diego advises against buying Caulerpa prolifera.
“If you already have it and you need to clean out your aquarium, do not put it in the gutter, down the storm drain or dump it into the bay,” said Mahen.
Instead, the Port advises draining aquariums that contain the seaweed into sinks or toilets so that the water will circulate through a treatment plant, minimizing the threat.
