Positive effect of fiddler crabs on saltmarsh grass reverses in expanded range

by Mary Linabury, LTER Network
June 04, 2024

In 2014, Dr. David Johnson was walking within a muddy salt marsh an hour north of Boston at the Plum Island Ecosystem (PIE) LTER when an Atlantic marsh fiddler crab, Minuca pugnax, scuttled across his path. These crabs are common residents of intertidal salt marshes along the eastern US coast; however, this crab was living in a new zip code. Dr. Johnson’s encounter marked the first documented M. pugnax this far north.

Migration of M. pugnax may be particularly impactful to local ecosystems, given that these burrowing crabs are ecosystem engineers. Like earthworms in soil, fiddler crab burrowing aerates soils to increase root respiration and decomposition of soil organic matter while also enhancing nutrient availability through fecal inputs. Fiddler crabs form an important commensalism with Spartina alterniflora in their historic range, a grass that is essential to the foundation of saltmarsh ecosystems.

But whether fiddler crabs maintained the same commensalism with Spartina in their newly expanded range was unknown. In a new paper published in Ecology, graduate student Kayla Martinez-Soto and Dr. Johnson determine how the interaction between the Atlantic marsh fiddler crabs and Spartina grass changes at different latitudes. They find that the pattern flips as crabs migrate north: the commensalism that benefits Spartina in the crabs’ historic range changes to an inhibitory relationship in the north.

Keep reading: https://lternet.edu/stories/positive-effect-of-fiddler-crabs-on-saltmarsh-grass-reverses-in-expanded-range/

Read the Ecology paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4203