A New Diatom from the Apostle Islands, Named for Ecologist Joan Elias

The sandspit at Outer Island, Apostle Islands National Lakeshore. NPS.

Joan Elias, the NPS Great Lakes Network's first aquatic ecologist, now retired, has had a newly discovered diatom named in her honor: Semiorbis eliasiae. On hearing the news, she said, "I thought I had to be dead!"

What diatoms tell us

• Diatoms are algae with cell walls of silica.
• When they die, parts of those walls — frustules — sink into lake-bottom sediment and are preserved like tiny bits of glass.
• Each species has its own frustule pattern, so species can be identified.
• Because the mix of diatom species shifts as conditions change, scientists use them to monitor lakes and rivers — and the layers of frustules in sediment record water quality going back hundreds of years.

The discovery

• Who: Mark Edlund of the St. Croix Watershed Research Station identified the new species in the rare genus Semiorbis. He has been collecting diatoms since 1987 and had found the genus only twice — Outer Island being one of those places.
• Where: a sediment core collected in 2007 from the lagoon on Outer Island, one of the farthest of the 22 islands of the Apostle Islands, in the Wisconsin part of Lake Superior. The lagoon is a wetland on the island's south side. Live colonies were also collected there in 2015.
• How: many lines of evidence, including comparisons with collections from Canada, Norway, New Jersey and Florida and differences in the structure of its shells.
• Range: so far, the Outer Island lagoon is the only place it is known — though it may yet be found elsewhere.

The Apostle Islands National Lakeshore in southwestern Lake Superior; the arrow marks Outer Island lagoon. NPS.

An uncertain home

• In September 2014, a large storm breached the longshore bar that separated the lagoon from Lake Superior, turning it into a cove.
• By July 2020, a sandbar had cut off about one-third of the original lagoon from the lake again.

Where it is kept

Specimens are preserved in the diatom collections of the Academy of Natural Sciences in Philadelphia, the Canadian Museum of Nature, and the Science Museum of Minnesota. The discovery was published in Diatom Research (DOI).

Sources

Based on "I Thought I Had to Be Dead!", National Park Service, Great Lakes Inventory and Monitoring Network; a work of the United States government in the public domain. The Outer Island photograph is from the NPS Gallery, public domain; the portrait and micrographs credited to the St. Croix Watershed Research Station are left out.