Award: OCE-1514893

Our results demonstrate that the invasive crab predator Carcinus maenas population in Seadrift Lagoon, Stinson Beach, CA underwent overcompensation in response to attempts to locally eradicate this population. After five years of active crab removal (2009-2013) resulting in >90% reduction of the adult population, the population underwent a 30 fold increase resulting in three times more crabs than the pre-removal level (2009). The 2014 population was heavily dominated (>97%) by small crabs. We found that following this population explosion the population in 2015 was substantially reduced with many fewer juvenile crabs. Other populations in the region that were similarly surveyed did not have any significant increase in population size in contrast to Seadrift. Mesocosm cannibalism experiments showed high levels of size-specific cannibalism by adult crabs on recruiting juveniles, which models indicate can easily explain the dynamics we witnessed. Additional molecular data not supported by this project strongly supports the idea that this population is almost entirely self-recruiting. We also found evidence, though limited, of early maturation with females reproducing at a smaller size consistent with overcompensation predictions. In summary, the results of this study provide convincing evidence of the first experimental demonstration of overcompensation following population reduction in a marine system. These conclusions have important implications for invasive species management as well as for fisheries management and other activities that involve harvest or other population reduction activities. Last Modified: 04/23/2017 Submitted by: Edwin D Grosholz