When Sabato "Simon" Rodia started work on what eventually became the Watts Towers in the 1920s, no one -- perhaps not even the artist himself -- knew exactly what he was building.
But, it turns out, he may have inadvertently created a time capsule for Southern California's marine ecosystems.
Each of the 17 structures that make up the famous landmark in South L.A. is covered in pieces of ceramic shards, broken bottles, and other ephemera, including at least 7,700 sea shells.
The seemingly random assortment of shells caught the eye of Bruno Pernet, a professor of marine biology at CSU Long Beach, when he first visited in 2009.
Pernet had just moved to Southern California and had wrapped up work on a survey of clams in Alamitos Bay. The way the shells were arranged on the mortar surface piqued his interest, because they appear to be arranged by shape or size alone.
"You can think of the whole assemblage of shells as a sort of museum collection, albeit one without any labels," he says.
He was determined to find out more about where the shells came from, but it wasn't until he returned from a sabbatical in 2012 that he started work on cataloging as many of them as he could.
But mollusks and gastropods -- think clams, sea snails, and oysters -- aren't his area of expertise.
"I just didn't know all those species by sight, certainly, and I didn't even know some of their names at all," Pernet says.
He eventually recruited Paul Valentich-Scott from the Santa Barbara Museum of Natural History to help catalog and identify the shells, but even for an expert, it was no easy task.
Most of the clam shells are embedded with their interior sides pressed into the mortar itself, making it impossible to see important identifying features. To get around that snag, they looked at unique ribbing patterns and other minute details on the shells to differentiate them as separate species. Pernet had to use a small stepladder and even binoculars to take a closer look at shells embedded farther away, including some that are on the taller structures.
In the end, they counted 34 species of animals -- all but five are native to Southern California's shorelines. The two men published their findings along with fellow researcher Emma R. Silverman earlier this month in the Journal of Conservation and Museum Studies.
Based on interviews with those who knew him, it's likely that Rodia picked up most of the shells himself from the 1920s to the 1950s during trips to the rocky tidal areas of San Pedro, or on the calmer beaches of Long Beach, which Rodia briefly called home before decamping to Watts.
"But the one striking thing," Pernet says, "is the rarity of non-native species [on the Towers] that are now very common in Southern California habitats."
The vast majority of shells come from two species of what's commonly known as California venus clams, and they typically live in low wave-energy protected habitats like bays and estuaries.
The Watts Towers study shows just how much more abundant the Venus clams were in Rodia's time. After decades of urban development, these clams have seen their natural habitats shrink dramatically, and today they are vastly outnumbered by invasive species of clams instead.
The Towers also feature a handful of black abaloneshells, which have all but completely disappeared from Southern California, though they were relatively easy to find on local beaches when Rodia was collecting shells for his project.
Though there are no extinct or critically endangered species represented at Watts Towers, the relative scarcity of the shells that currently adorn them could be a problem for those trying to preserve the landmark in its original form. While California venus clams, for instance, are still around, finding their shells in the hundreds to replace any originals on the Towers would be difficult.
And since shells naturally erode or break, Pernet says some of the non-native species on the structures may have ended up there over the years by conservationists trying to replace original pieces.
"That's part of what makes this an original work of art," he says, "The fact that so many of these small pieces simply can't be replaced."
