2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ...

Bolsa Chica Lowlands Restoration Monitoring2007 Annual Report1.7. NON-NATIVE INVASIVE SPECIESAn awareness of the importance of tracking the arrival and spread of non-native species has increasedin recent years, particularly with the discovery of the invasive non-native seaweed Caulerpa taxifoliain nearby Huntington Harbour and in Agua Hedionda Lagoon in San Diego County. Early detection ofsome species of invasive plants and animals may allow the opportunity for quick and economicalresponse activities. These species may include non-native seaweeds such as Caulerpa spp., Sargassumfilicinum, and Undaria pinnatifida, or terrestrial weed plants such as pampas grass or Arundo, asmentioned above. However, there are other non-native species that are already proliferating inregional coastal embayments and are likely to invade the tidal areas of Bolsa Chica at some point in thefuture. While options to restrict these species from Bolsa Chica are limited, keeping good records onthe time of arrival and the degree of spread can be helpful for understanding the threat posed by thesespecies to Bolsa Chica, as well as for the general body of knowledge about these species.During the first year several non-native marine species wereobserved. Japanese wireweed (Sargassum muticum) is aseaweed native to Japan that is widespread in SouthernCalifornia bays, commonly found on rock, riprap, or otherhard substrate. This brown alga has been documented tocompete with and displace native species of seaweed andeelgrass by reducing light through shading. At Bolsa Chicathe seaweed has not yet colonized the riprap, rather wasobserved in late 2007 in the open water of the FTB. Theholdfasts of the seaweed were secured to speckled scallops(Argopecten ventricosus), which were serving as mini-reefsSargassum muticum attached to a speckled scallop.for the S. muticum to settle onto. It is estimated that up to 100such pairings occurred throughout the FTB in December 2007. It is likely that hard substrate withinthe basin will become colonized with S. muticum following future reproductive events by thepopulation on the scallops. There are no feasible means to control or prevent colonization by S.muticum, nor is its potential biological impact clearly understood in southern California.The Japanese mussel (Musculista senhousia) is another non-native that would inevitably arrive atBolsa Chica. This species settles from the plankton onto soft substrate and can form dense mats ofentangled fibrous threads. This mat and the thousands of mussels that can colonize per square metercan inhibit the feeding of native filter feeders and the spread of eelgrass. Although there is noevidence of dense mats having formed at this time at Bolsa Chica, the capture of several individuals inthe fishing nets indicates their presence in both the Muted Pocket Marsh and the FTB. There is noeffective means to control this species, however it has been documented that dense, healthy eelgrassbeds can inhibit the growth of M. senhousia (Allen and Williams, 2003).There are numerous terrestrial non-native species in the wetlands of southern California, however theBolsa Chica Lowlands are fortunate to be devoid of two of the most invasive and difficult species.There is little to no occurrence of the giant reed (Arundo donax) or pampas grass (Cortaderia selloana)within the study area. Any observations of these species will be immediately reported to theDepartment for removal. Ice plant (Carpobrotus edulis) is widespread in the system and is beingremoved by Department and volunteer hand labor as time permits. It is likely that herbicide controlwould benefit the control or eradication of this species from the wetlands.Merkel & Associates, Inc. 57