Eradication Efforts Underway for Invasive Algae In The Cays

After discovering an invasive species of algae in the bay waterways in the Coronado Cays while performing a routine environmental survey before a dock replacement project, Marine Taxonomic Services (MTS) have been leading efforts to eradicate the species before it spreads and causes disruption to the south San Diego Bay wildlife habitat.

MTS is part of a larger Southern California Caulerpa Action Team (SCCAT), and I spoke with Doctor Robert Mooney —the organization’s vice president, principal consultant, and project manager— about those efforts.

Mooney has been active as a marine biological consultant in Southern California for over 20 years and was part of the teams that eradicated previous Caulerpa infestations in the region. “We had an invasion of Caulerpa taxifolia in the early 2000s where it was found in the lagoon in Carlsbad,” he mentioned. “At the time, I was working for Merkel and Associates, who is also working on the current Caulerpa eradication effort with us.”

The publication of that discovery contributed to the discovery of Caulerpa taxifolia in a saltwater lagoon in Huntington Beach as well. “We worked to eradicate both of those [infestations],” Mooney said of what was a years-long effort. “That was declared successfully eradicated in 2006, and one of the things that came out of that work was the realization of the problem of Caulerpa.”

Mooney explained that while the Caulerpa genus is not unusual to find around the world, the rapid nature of its growth has made it a problem in non-native habitats in oceans and seas on a global scale. “Caulerpa taxifolia was already listed as a federal noxious weed at the time, which prevented it from crossing state lines and from being imported, but it was still legal to possess it for your aquarium,” he noted of the regulations around the algae in the early 2000s.

“One of the things that came out of the eradication work at that time was a ban on nine Caulerpa species,” Mooney continued, adding that the genus had been very popular as both aquarium tank decoration and as natural filters for refugium tanks. “California law in the early 2000s attempted to ban the whole genus, but there was some pushback from the aquarium industry and so the nine species that were thought to be potentially the most invasive, or that looked most like Caulerpa taxifolia, were banned, but not all of them.”

In areas so close to bodies of water, Mooney described how easy it is for Caulerpa to be released into the wild, even unintentionally. “You might not think you’re dumping something in the ocean if you rinse a tank in your driveway or something like that, but your storm drain may just be feet away from the ocean.” Dense patches of Caulerpa can grow from even a single centimeter-sized segment of the algae.

Among the non-banned species from the initial regulatory action was Caulerpa prolifera, which is the species that was found in the Cays. “Now, because of this infestation, the entire genus has been banned in California, and it’s now illegal to possess any Caulerpa species in California,” Mooney told me.

The legislation in the 2000s also created the Caulerpa Control Protocol, which established that Caulerpa surveys had to be performed before projects that could potentially disturb the sea bed were implemented. “It’s a good idea; you put a biologist in the water, and if it’s not Caulerpa, maybe it’ll be early detection of something else,” Mooney noted. “And that’s what happened in this case [with the discovery of Caulerpa prolifera].”

In this area of the San Diego Bay, Caulerpa prolifera poses a real threat to the native eelgrass as Caulerpa’s growth rate would overtake it. “And if it got off-shore, it could potentially smother our native kelp forests and things like that,” Mooney added. The invasive effect of the algae could then compound on a large scale, negatively impacting fisheries and the ecosystem as a whole. Were Caulerpa to spread in the southern portion of the San Diego Bay, it could lead to the loss of the native sea turtles in the area, which thrive on the eelgrass.

To ensure this doesn’t happen, Mooney, his team, and their SCCAT partners have been busy over the past few weeks laying down barriers to prevent any further spread of Caulerpa prolifera from where it has been located and mapped out as part of earlier surveying efforts around the Cays. After taking immediate action on the initial infestation located around the dock in Antigua Court, the current efforts have been focused on the additional patches found in the canals between Antigua Court and Green Turtle Road.

“We’ve placed plastic mats on the sea floor which block sunlight to the Caulerpa and kill it in place,” Mooney described of the barrier program. “The mats are sealed to the sea floor with a combination of rebar and sandbags, which kind of seals it off and just lets it die under the barriers.”

As Caulerpa relies on segmentation only to reproduce rather than seeds or spores that could more easily be carried much farther in the water, he added that, “While it’s terrible how easily it can spread through fragmentation and how fast it grows, it can only get so far ahead of us. So as long as we capture all of it, we can potentially beat it.”

While this area of the bay presents visibility challenges due to the shallowness of the mudflats creating turbid, murky water, Mooney mentioned that conditions are fairly good in regards to lower chances of Caulerpa spreading. “Caulerpa was also discovered in Newport Bay, the same species of Caulerpa prolifera, in 2021. There, it was close to the entrance [of the bay], and there was a lot of boat traffic and tidal surges, so we really worried about it getting offshore if we didn’t do something absolutely immediately.

“In the Cays,” he continued, “it’s actually almost an ideal situation in that you have calm water and low tidal exchange, so these fragments, when they’re generated, aren’t being picked up and moved except by maybe boat vessel currents and prop wash.”

He added that in spite of the low visibility, Caulerpa prolifera is bright green and as the, generally, singular feature the divers have come across in the canal site, has be easily identifiable. “We’ll be swimming along, and it’s pretty much, ‘bare bottom, bare bottom, oh – there’s something growing here,’” he described of the survey process so far.

“But to get our arms around it and map it, we still have to deal with being very systematic,” Mooney also said. “We lay lines on the bottom for divers to follow, and divers essentially line up shoulder to shoulder and swim down those lines. Then the boat lays another line, and the boat operators are laying them in a very systematic fashion such that this line of divers is basically sweeping the entirety of the bottom as they go.

“[Divers] stop and alert the boat if they find Caulerpa, and the boat operator will take a GPS waypoint, and we build our maps from that data and those lead into the barrier plan,” he further explained of the process. About 10 to 14 members of MTS and their partners have been onsite each day they’re out there working to eradicate the Caulerpa prolifera, which typically include five or six divers, a boom lift operator to get materials onto the boats and to the divers, and boat operators tending to the divers and there safety in the water with other vessels.

“The barriers are just the first step of eradication. Now we’ll continue to survey,” Mooney said of their current efforts. “We need to systematically continue to survey because, as you can imagine, it’s not easy to do all of this underwater, and if you miss a single centimeter fragment, you come back in a couple of months, and it’s going to be a patch that’s a few feet across.”

Mooney had initial doubts about how effective they could, essentially, weed the ocean as he thought of it, when he first worked on eradicating the Caulerpa taxifolia infestations in the 2000s. But those earlier efforts, including the more recent Caulerpa prolifera outbreak in Newport, have proven that it can be done. “It’s just systemic surveys and a lot of hard work. With the right amount of determination, you can get it done,” he said.

“Things are going well in the Newport infestation. We’re at a point there where we think we’ve treated it all. We’ve monitored our sites there three times with no findings, and something similar will have to happen in the Cays,” Mooney added. He’s anticipating that the barriers will be in place for approximately a year, during which they will monitor the barrier to ensure none of the algae survives.

“We’ll cut some openings in the barrier to make sure Caulerpa does not grow from them, and that will pave the way for going ahead to remove the barriers,” he noted. Those decisions will be made by SCCAT as a whole, but from their current progress and findings, Mooney is personally estimating the full process to the all-clear will take a couple of years, similar to the timescale on the Newport eradication.

“Once we get to a point where we’ve got it all and we do our survey where we don’t find any, then we need to look at how effective our divers are at finding it, and take that effectiveness and multiply that by how many surveys we need to do in order to be comfortable that we’ve found it all,” he further explained. “So that process will take a couple of years, coming back periodically and doing surveys to make sure that we didn’t miss anything while treating it.”

He also mentioned that currently, signs have pointed to no larger spread of Caulerpa prolifera in the southern area of the bay. “We’ve got these big patches, surrounded by small patches, surrounded by nothing. We have found a couple of further removed [fragments], but nothing towards the mouth of the Cays leading into to the San Diego Bay, where we have surveyed a fair area.

“But the next step, too, is to look further afield, so the U.S. Fish and Wildlife Service has provided funding to do more surveys in south San Diego Bay proper,” he added. “We’re going to start looking there to make sure that this isn’t coming in from somewhere else.” While he’s hopeful that won’t be the case due to the lack of any Caulerpa trails, there’s still the possibility that a fragment could have been carried by an anchor or something of that nature.

The Coronado Cays Homeowners Association (CCHOA) has been working diligently with Mooney’s team and SCCAT to assist with and keep Cays residents aware of the Caulerpa issue. “The support from the Coronado Cays Homeowners Association has been tremendous,” Mooney said of their partnership. CCHOA General Manager, Henry Angelino, has continually kept residents updated on the eradication process and what they can do to help prevent further spread of the algae.

“I am relieved that the invasive algae is covered with a barrier and being eradicated,” Angelino mentioned of the ongoing efforts. “Boaters must still be careful around the infested areas so as not to disturb the barriers. Future surveys will tell if the eradication efforts were effective but we have taken a big step forward to eliminating Caulerpa in San Diego Bay.”

If boaters are using their boats in canals, precautions include cleaning their boats, transiting only at high tide and at no-wake speeds, and getting vehicles in and out of slips with minimal thrust so as to cause as little disturbance to the barriers as possible. Additionally, Mooney recommends that should anyone spot an algae, to take a photo of it and report so his team and SCCAT can identify it.

“As summer approaches, please be mindful of the team flying diving flags,” Mooney also added. “Feel free to wave and say hi, but please keep a safe distance.”

VOL. 114, NO. 12 - Mar. 20, 2024