Rediscovery of Endemic Maryland Isopod

Written by Pallieter de Smedt

The terrestrial isopod fauna of North America is poorly studied mostly because the low number of native species. Most non-native species were introduced from Europe, successfully colonized virtually all habitats, and became extremely abundant. Woodlice (Isopoda: Oniscidea) are decomposers and crucial for nutrient cycling, litter decomposition and water retention, thus detailed knowledge on the distribution of both native and non-native species is important to understand their effect on ecosystem functioning. As part of an ongoing collaboration between Dr. Pallieter De Smedt, University of Ghent, Belgium and Dr. Katalin Szlavecz, Johns Hopkins University, Baltimore, MD, the entire state of Maryland was surveyed to create distribution maps for all terrestrial isopod species. The team discovered many new state records of both native and non-native species increasing the species list by 50%. However, they failed to find one species, the elusive Scyphacella arenicola that had not been seen for 120 years in the state.

Scyphacella arenicola is a native species, endemic to the East Coast of North America with only a handful recent records in other states. With the help of the Smithsonian National Museum of Natural History and Nathan Jones from the American Isopod and Myriapod Group (AIMG), old records were verified and data on the habitat was gathered. The last Maryland record is dated back to 1905 with a vague locality description, such as the “mouth of the Choptank River.” Based on the specimens in the Smithsonian National Museum of Natural History and old literature, the team obtained a better idea about the ecology of the species. Scyphacella arenicola is a coastal species of about 5 mm long, which burrows in the sand. Targeted field surveys on beaches along the Chesapeake Bay were carried out.

After visiting over 50 beaches, a large colony was found along the Choptank river near Cambridge, and a second colony was discovered along the mouth of the Nanticoke river. Colonies of Scyphacella arenicola were found between the high and spring tide mark and can be recognised by numerous small sandy domes in this zone. The number of domes can be as a high as 80 per square meter. During the day, isopods burrow a few centimetres or deeper below the surface and come out only at night to forage. It appears that species thrives only on sheltered and undisturbed beaches without heavy trampling by humans. Beach tourism and subsequent destruction of this habitat is most likely the reason why the species has become so rare. More research is needed to better understand the large- and small-scale distribution and the ecology of this enigmatic endemic species.