THE ERADICATIONS

Agua Hedionda Lagoon is a 248-acre, fully tidal, coastal lagoon. Activities within the lagoon include boating, fishing and jet-skiing. The lagoon also serves as a source of cooling water for a power generating station. Caulerpa taxifolia was discovered in Agua Hedionda Lagoon by SCUBA divers monitoring the status of an eelgrass restoration program. When discovered, the infestation consisted of numerous dense patches, located primarily where native eelgrass beds had previously existed. Lagoon-wide surveys found additional Caulerpa taxifolia concentrated in five areas further east in the lagoon. In total, approximately 0.13 hectare of Caulerpa taxifolia was distributed over a 42.3-hectare (104.6-acre) area of the eastern basin. The western-most occurrence was 1.2 km (0.7 mile) from the outlet of the lagoon to the Pacific Ocean. Caulerpa taxifolia was likely released from a home aquarium into the lagoon either directly or through one of the storm drains that empties into the lagoon.

A review of previous international attempts to eradicate Caulerpa taxifolia revealed no effective treatment approaches for large-scale infestations, due to issues such as incomplete treatment or dispersal of algal fragments. Therefore, simultaneous with initial survey efforts and formation of SCCAT, containment and treatment investigations were initiated through the testing of hand picking, dredging, tarping and herbicide application approaches, both in the field and laboratory. Application of chlorine bleach proved the most promising treatment, due to the lethal effect on Caulerpa taxifolia, readily detectable effect (visual bleaching), ease of application, low cost, and non-toxic residuals. The tendency of Caulerpa taxifolia to easily fragment and grow into new plants from even very small fragments dictated that the Caulerpa taxifolia should be treated in-place, with minimal disturbance.

In order to provide full containment of patches and fragments of Caulerpa taxifolia during treatment, while minimizing the impacts of chlorine application to surrounding waters, a tarping approach was adopted. This approach is outlined in the Revised Eradication Plan for Caulerpa taxifolia in California (Merkel & Associates, 2001). Divers covered patches of Caulerpa taxifolia with black PVC tarps that were sealed to the bottom with rebar and sandbags. Initially, tarps placed over large patches of Caulerpa taxifolia in Agua Hedionda Lagoon were fitted with ports, and liquid chlorine (sodium hypochlorite) was pumped under the tarps from storage tanks on shore. In later treatments, and in Huntington Harbour, solid chlorine tablets (trichloroisocyanuric acid) replaced the liquid treatment for safety and ease of application in areas of reduced biomass.

All eradication activities conducted at each site were regulated through U.S. Army Corps of Engineers Nationwide Permit Number 25 and Regional General Permit No. 64, a California Coastal Commission Consistency Determination, a Research Authorization and Special Local Need Registration issued by the California Department of Pesticide Regulation, and a Notice of Exemption (CEQA). Due to the ease with which Caulerpa taxifolia can be spread and for the safety of the divers conducting the work, active treatment areas were closed to public access until all patches were covered and treated.

Treatment activities in Huntington Harbour began in October 2000 following intensive mapping efforts. Tarps were secured to the bottom, with solid chlorine tablets placed underneath to treat the widely distributed Caulerpa taxifolia. Following the completion of the initial treatment in February 2001, follow-up surveys to detect and treat remaining Caulerpa taxifolia were initiated using techniques similar to those developed at Agua Hedionda Lagoon. Due to the small size of the area to be examined, surveys could be completed in three days, allowing for numerous repeated surveys to be conducted with the funding available. Additional tarps were added, as needed, to treat additional patches when discovered, with most treatment activities being completed by summer 2001. There were fewer, and generally smaller, patches of Caulerpa taxifolia found in each subsequent survey. The total sizes of patches found in fall 2001, winter 2001, spring 2002, summer 2002, and fall 2002 measured 9.9 m2, 1.2 m2, 1.3 m2, 0.5 m2, and 0.5 m2, respectively. The last patch of Caulerpa taxifolia was found and treated on November 19, 2002. Quarterly surveys continued for the next three years. No Caulerpa taxifolia has been detected in 13 additional surveys, conducted over three years through December 2005.

Although initial surveillance indicated that the infestation was restricted to a small area in the northern portion of Huntington Harbour, two harbor-wide surveys of the remaining areas were conducted by teams of divers spaced one meter apart. Full surveys of the entire harbor were conducted in 2001 and again in 2005. Caulerpa taxifolia was not detected elsewhere in the harbor.

ASSESSMENT OF SURVEY TECHNIQUE

As fewer and smaller occurrences of Caulerpa taxifolia were being discovered during the eradication effort, a program was developed to assess the survey dive team’s ability to locate Caulerpa taxifolia in the often murky water of the infestation sites. Patches of artificial Caulerpa of various small sizes were randomly placed at Agua Hedionda Lagoon and Huntington Harbour during each of the regular surveys to test the dive team. Confidence in the results of each survey for live Caulerpa taxifolia could then be quantitatively estimated based on the proportionate amount of known quantities of artificial Caulerpa found by the divers. The results of the consecutive assessments of the efficacy of the surveys ultimately allowed for an estimation of the eradication certainty that all real Caulerpa taxifolia existing at the two sites had been found and that eradication had been achieved.

The Southern California Caulerpa Action Team set two criteria to be met to achieve the stated goal of eradicating Caulerpa taxifolia from Agua Hedionda Lagoon and Huntington Harbour. The criteria for each site are:

Criterion 1) The containment and lethal treatment of Caulerpa taxifolia at the infestation site.

Criterion 2) The verified absence of Caulerpa taxifolia from the infestation site.

The degree to which these criteria have been met under the current program is discussed below in the context of evaluations of treatment approach, the biology of Caulerpa taxifolia and the measured capabilities of the survey team.

CRITERION 1

Prior sections of this report have reviewed the evidence that the treatment method applied was lethal to Caulerpa taxifolia at both infestation sites. The laboratory assessment of the viability of Caulerpa taxifolia in sediment from treated areas found no evidence of Caulerpa taxifolia regrowth. Field assessments of study plots that had been infested with Caulerpa taxifolia, treated, and then later exposed to the open water found no evidence of Caulerpa taxifolia regrowth after more than three and a half years of monitoring at Agua Hedionda Lagoon and for over four and a half years in Huntington Harbour. Based on these studies, there is a very high degree of certainty that Criterion 1 has been met.

CRITERION 2

Intensive, systematic surveys of the infestation sites, over three years since the last detection of Caulerpa taxifolia, found no persisting Caulerpa taxifolia. Recognizing that the remaining occurrences were likely to be very small in size, the quality control procedure described above was implemented to quantify the ability of the survey team to detect small Caulerpa taxifolia in the challenging environmental conditions present at the infestation areas. The results of these assessments were used to estimate an eradication certainty at Agua Hedionda Lagoon of greater than 99 percent based on the average conditions, or greater than 97 percent based on worst-case conditions. An estimate of well over 99 percent eradication certainty can be made at Huntington Harbour under all conditions.

These estimates of eradication certainty are conservative, recognizing that while the survey efficacy assessment studied the probability of detecting a fixed number of objects of a static size (artificial Caulerpa), live Caulerpa taxifolia is biologically active and capable of expanding to larger sizes over time and multiplying in number. Additionally, Caulerpa taxifolia was not randomly distributed over the infestation sites, but rather clustered in certain areas, which allowed for more intensive scrutiny focused in these areas. As noted above, the estimated time for a small fragment of Caulerpa taxifolia to grow to a size large enough to be found every time (one meter wide) was two growing seasons. Given that intensive surveillance was continued through three full growing seasons at both infestation sites without detection of Caulerpa taxifolia, there is a very high probability that Caulerpa taxifolia is no longer present at these sites and that Criterion 2 has been met.