The colonization pattern of the Atlantic marsh fiddler crab, Minuca pugnax (Smith, 1870) (Decapoda: Brachyura: Ocypodidae), in its northern expanded range of New Hampshire, USA

As ocean temperatures increase, the fiddler crab Minuca pugnax (Smith, 1870) has expanded its historical range northwards from Cape Cod, Massachusetts, US and is now found as far north as central Maine. We aimed to further determine the population distribution of M. pugnax in its newly established range in New Hampshire by examining tidal marshes along the open coast and estuaries. Coastal and estuarine marshes often exhibit differences in temperature, salinity, tidal range, and sediment type, which may impact the colonization ability of fiddler crabs. In this study, fiddler crab burrow abundance, as well as environmental factors such as plant community and sediment type, were measured using 20 quadrats (0.25 m × 0.25 m) along a 200-m section of creek bank across two open-coast tidal marshes and three estuarine tidal marshes. An imaging “burrowscope” was used to measure burrow occupancy, which helped determine population estimates. Our analysis shows a low overall abundance of M. pugnax with higher populations in the warmer estuarine marshes of Great Bay and Hampton Seabrook than in the open coast marshes of New Hampshire. The sites with the highest M. pugnax abundance also exhibited the lowest soil compactness. Overall, these findings suggest a relationship between M. pugnax abundance and both temperature and soil compactness, indicating a potentially greater suitability of tidal marshes in warmer estuarine environments to the range expansion of M. pugnax. Population expansion of M. pugnax warrants monitoring due to its potential impacts on tidal marsh plant health and overall marsh resiliency, which may further threaten marshes already facing severe pressure from rising seas and human development.