The invasive Asian shore crab (Hemigrapsus sanguineus) was discovered on the east coast of North America in 1988 in southern New Jersey, arriving in Long Island Sound (LIS) estuary ca. 1994. To follow the development of the invasive population and its impact on resident crabs, quadrat sampling of cross-intertidal transects has been used to estimate the June population density since 1998 and the population size structure since 2005 at a western LIS site.
After initial exponential population growth (1998-2001), June intertidal densities have fluctuated, but H. sanguineus has driven the near extirpation of resident crabs. The average size (carapace width) of male and female crabs in the intertidal zone declined by ca. 20% from 2005-2016, with an overall rate of decline of 1.6% yr-1. In particular, the relative abundance of the larger size classes of both sexes declined significantly over this period. Smaller crabs resulted in a 60% decline in biomass density. Comparison of size-frequency distributions from the home range with early (2005) and late (2016) LIS populations reveals the loss crabs ≥32 mm CW from the intertidal zone of the invaded site. The change in size frequency distribution of females has consequences for reproductive output; areal productions of embryos (no. m-2) has declined ca. 65% since 2005, tied significantly to declines of the larger (≥ 24 mm CW) female size classes. The data set will be updated with the 2017 census.