I Thought I Had to Be Dead!

Retired aquatic ecologist, Joan Elias.

Mark Edlund/St. Croix Watershed Research Station

It may not carry the same panache as being knighted by the Queen of England or being inducted to the Rock and Roll Hall of Fame, but Joan Elias, the Great Lakes Network’s first aquatic ecologist, has been immortalized in the form of a diatom named in her honor: Semiorbis eliasiae.

When told about this honor, Joan said, "I thought I had to be dead!" Fortunately for everyone involved, she is not required to be dead. The diatom, though, is very much dead.

Diatoms are a type of algae with cell walls made of silica. When they die, portions of the cell walls called frustules settle into the bottom sediments and are preserved like tiny bits of glass. Different species of diatoms can be identified by the unique patterns of their frustules. We use them to monitor environmental changes in lakes and rivers because the diatom community composition shifts in response to such changes. Thus, the layers of frustules contained in bottom sediments provide a history of water quality going back hundreds of years.

The diatom Semiorbis eliasiae. Left to right: a light microscope image of the diatom valve or shell, a light micrograph of a live colony of Semiorbis eliasiae, and a scanning electron micrograph of a single cell.

Mark Edlund/St. Croix Watershed Research Station

Mark Edlund at the St. Croix Watershed Research Station identified the new diatom, which is one of only three other species in the genus Semiorbis. The new species came from a sediment core collected in 2007 at Outer Island lagoon in the Apostle Islands, an archipelago of 22 islands in the Wisconsin portion of Lake Superior. Outer Island is, as the name suggests, one of the furthest out from the mainland. The lagoon there is a wetland on the south side of the island.

“The genus Semiorbis is really uncommon. I’ve been collecting diatoms since 1987 and have only found it twice. Outer Island is one of those places”, says Edlund. Live colonies were also collected from Outer Lagoon in 2015.

The Apostle Islands National Lakeshore (Wisconsin) in southwestern Lake Superior. The orange arrow shows the location of Outer Island lagoon.

NPS

“We used many lines of evidence to determine this is a brand new species including comparisons with other collections from Canada, Norway, New Jersey, and Florida, and looking at differences in the structure of its shells. So far, the Outer lagoon is the only place Joan’s diatom is found. It may be in other places, but just not found yet.”

If the Outer lagoon created a unique environment for Semiorbis eliasiae, the fate of that environment is in question. A large storm in September 2014 breached the long-shore bar that separated the lagoon from Lake Superior, essentially creating a cove. However, by July 2020, about one-third of the original lagoon had been re-isolated from Lake Superior with a sandbar.

Specimens of Semiorbis eliasiae are permanently preserved in diatom collections at the Academy of Natural Sciences in Philadelphia, The Canadian Museum of Nature, and the Science Museum of Minnesota. A paper announcing the discovery was published in the journal Diatom Research (DOI: 10.1080/0269249X.2021.1875053).