The Atlantic marsh fiddler crab, Minuca pugnax (Smith, 1870), is a climate migrant that recently expanded its range northward into the Gulf of Maine. We tracked the M. pugnax population within the Great Marsh, in northeastern Massachusetts, USA, since it was first detected in 2014 using burrow counts. Because burrow counts can overestimate fiddler-crab density, we used camera traps to determine the relationship between burrow densities and fiddler-crab densities in 2019. The burrow count surveys show a six-fold increase in the density of M. pugnax in the Great Marsh from 2014 to 2019. Results indicates that the fiddler-crab population in the expanded range is established and growing. Based on burrow counts, however, the density of M. pugnax in the expanded range (6 burrows m^–2) remains much lower than those found in the historical range (up to 300 burrows m^–2). Based on the camera traps, we determined that burrow counts overestimated fiddler-crab densities by 47% in 2019. There was, on average, one crab detected for every two burrows observed. This result suggests that estimates of densities of M. pugnax based on burrow counts should be reduced by half. Minuca pugnax is an ecosystem engineer that can influence saltmarsh functioning and the magnitude of that influence is related to its density. Our results imply that the populations of M. pugnax in the expanded range are currently having minor impacts on marshes relative to larger populations in the historical range, but their impact will increase as the populations grow.

中文翻译：

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在美国缅因州湾范围扩大的大西洋沼泽提琴蟹的密度（Minuca pugnax，Smith，1870年）（十足目：Brachyura：Ocypodidae）

大西洋沼泽提琴蟹Minuca pugnax（史密斯（Smith，1870年）是一名气候移民，最近将其范围向北扩展到缅因湾。我们追踪了美国马萨诸塞州东北部大沼泽地中的八哥松鼠种群，因为该物种于2014年首次使用洞穴计数被发现。由于洞穴计数可能会高估小提琴蟹的密度，因此我们使用相机陷阱来确定2019年洞穴密度与小提琴蟹密度之间的关系。洞穴数调查显示，大沼泽地的松柏密度提高了六倍。从2014年到2019年。结果表明，扩大范围的提琴螃蟹种群已经建立并正在增长。但是，根据洞穴数，沙棘松鼠的密度在扩展范围内（6个洞穴m ^–2）仍远低于历史范围内（最高300 m ^–2的洞穴）。根据摄影机的陷阱，我们确定到2019年，洞穴的数量被高估了小提琴蟹的密度，为47％。平均而言，每观察到两个洞穴，就会发现一个螃蟹。该结果表明，根据洞穴数估算的印度松果密度应减少一半。Minuca pugnax是一位生态系统工程师，可以影响盐沼的功能，这种影响的程度与其密度有关。我们的结果表明，M。pugnax的种群 相对于历史范围内的较大种群，目前范围扩大的沼泽对沼泽地的影响较小，但随着种群的增长，其影响将增加。