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Old Salt Lake | Virtual Museum

Exhibit 48

[ Page updated: February 17, 2021 ]

A Group of Kelp Flies in the Wrack Zone

[Figure 1 - February 10, 2021 photograph of Torrance Beach looking south to Malaga Cove showing wrack line.]

"The wrack zone or wrack line is a coastal feature where organic material (e.g kelp, seagrass, shells) and other debris is deposited daily at high tide. This zone acts as a natural input of marine resources into a terrestrial system, providing food and habitat for a variety of coastal organisms."

The full Wikipedia web page with more text about the wrack zone is at:

Illustration of the anatomy of a beach from the U.S. National Park Service:

[Figure 2]

Random bunch of kelp in the wrack line of Torrance Beach on February 10, 2021:

[Figure 3]

Close-up of a part of the above bunch of kelp showing a group of kelp flies. To see these flies moving around, see the two videos below.

[Figure 4]

This exhibit originally described this species of fly as probably being Coelopa frigida. Fortunately, an identification and description of the species was kindly provided by Emile Fiesler, President of BioVeyda, Minimally-invasive Biological Inventories, Surveys, and Biodiversity Assessments. Emile writes:

"The species is likely Coelopa (Neocoepola) vanduzeei as C. frigida does not occur on our west coast. Coelopa (Neocoepola) vanduzeei was first recorded by Frank R. Cole from Laguna Beach in 1912, but he presumed it was Coelopa frigida.

C. vanduzeei was first described by Ezra Townsend Cresson jr.: male holotype, La Jolla, California, March 7, 1914. It occurs from Baja California (Mexico) north to Alaska and is only found on beaches along the coast, associated with marine algae, and predominantly with various kelp species, where they often aggregate in large numbers, especially in the summer, but also in the winter. Their larvae feed on kelp."

The UC Santa Barbara Natural Reserve System has a photograph of the fly and more text description - here

Video 1 of the kelp flies in the kelp.

This video (MP4, 23 MB, 10 seconds) is a close-up of the above kelp showing movement of the kelp flies and includes an appearance by a bee.

Video 2 of the kelp flies in the kelp.

This video (MP4, 64 MB, 30 seconds) is another close-up of the above kelp showing movement of the kelp flies and includes a pan to the water with an appearance by a shorebird.