Halting an invasion surge of non-native mangroves in a Southern California tidal saltmarsh while engaging the local community

Contrary to predictions, the grey mangrove, Avicennia marina var. resinifera, expanded into vegetated tidal saltmarsh in Mission Bay, San Diego, California following its introduction from New Zealand in 1968.  The discovery in April 2006 of their re-emergence following a major removal effort in 1980 and subsequence control measures for two decades after led us to further studies of the demography, physicochemical preferences, and distribution mechanisms of this population, and mechanisms of natural saltmarsh ecosystem conversion. In 1980 the largest three trees, with 25 rings, were deduced to be the population's founders. Plants were observed to flower when large enough to have six rings, and to lay down 1-5 rings per year (Levin ,1980, unpublished.) .  In 2007 the largest plants have 19 rings, have grown from cryptic seedlings in fewer than six years, and reproduced with as few as four rings.  In April 2006, 7600 propagules were removed from the 98 fruiting plants and 5900 from the marsh surface, a total weight of 30 kg. From 2006-2007, the reproductive population increased from 98 to 380.  Based on the1980 harvest, r was estimated at 0.693 (Kay, 1993, unpublished).  Propagules in lab studies floated for 5 days, theoretically allowing broad dispersal, but mapping shows no expansion bayward.  In 2007 mangrove canopies with propagules attached were removed to prevent population expansion and to mitigate detrimental ecosystem engineering impacts; 430 shrubs were removed and characterized with 136 hours of volunteer and public agency effort.   Initial stable isotope analyses show that certain mangrove fauna have distinct stable isotope values from those in native Spartina, indicating that mangroves may affect salt marsh trophic structure.  The degree to which the mangrove control measures can restore the habitat to the pre-invasion condition is the focus of current investigations.