Even adult New Zealand Mud Snails, like the dark, conical ones in the middle of this leaf, are tiny: three to six can fit across the surface of a dime.
Federal and state land managers know that southern California's rivers and creeks are under increasing threat from New Zealand mud snails. The tiny pests can change the food chain and squeeze out native animals. A new survey of the Malibu Creek watershed finds the snails spreading for the third year in a row. KPCC's Molly Peterson reports that not everyone agrees on what to do about them.
Molly Peterson: Solstice Canyon is a thumb of national parkland in the Santa Monica Mountains, with a clear cold creek running through. It appears pretty untouched – unless you know what you're looking for.
Mark Abramson does. He monitors stream health for the Santa Monica Baykeeper. In his truck tailgate are huge plastic orange bags. In those are hip waders – crunchy, stiff, and disinfected after two days in a freezer. Abramson says he needs a clean pair for every site he visits.
Mark Abramson: We used to have only a couple pairs of waders, now I have 40 pairs of waders.
Peterson: Abramson's looking for tiny New Zealand mud snails. Nobody knows how they got to the United States. In this area, stream monitors may have tracked them in. Abramson doesn't want to do that.
Abramson: They just stick to you like aquatic hitchhikers, you go up to the next creek.
Peterson: As he walks upstream, Abramson picks up a leaf, then a rock.
Abramson looks hard at little riffles of fast water New Zealand Mud Snails like. Three mudsnails fit across a dime; the babies are smaller than poppy seeds. So often, Abramson finds them by touch – they're gritty.
Abramson: Feels like sand, right, so small you can't feel the shape of them, it's a little baby mudsnail.
Peterson: None of their usual predators keep these invasive mudsnails in check. And the mudsnails gobble up the bacteria and algae native snails and flies need.
Abramson: They just take up the entire bottom of the creek – all the gravel, all the sand, and that's where the little bugs live. And so that's like your dragonfly larvae before they emerge and fly away, your stone fly, your cattis fly, your mayflies – things that serve for fish food, newts, and if they're gone, you know, it's going to impact the whole food chain.
Peterson: This part of Solstice Creek is clean. But Jack Topel, from the Santa Monica Bay Restoration Commission, walks a lower reach of the creek. Everything he picks up carries snails.
Jack Topel: Trash, sticks, leaves, you name it. And they're doing fine here. Unfortunately.
Peterson: Surveys find snails at seven creeks – up from three creeks two years ago. Almost that far back, land managers and monitors like Abramson negotiated for a sign urging people to be cautious while they're in the watershed.
Abramson: Clean off your gear, whether it's sandals boots, waders, bikes, pets, and horses, so trying to deal with the custom recreation we have here. And don't go from stream to stream. That was the main message we wanted to get across.
Peterson: Abramson hasn't seen those signs at any site, including Solstice Creek. The National Park Service's Ray Sauvajot says that instead, federal kiosks in the Santa Monica Mountains carry smaller, simpler signs that leave out specific activities.
Ray Sauvajot: What we don't want to do is suggest to people that fishing is permissible or even encouraged when that can, in fact, contribute to having people come out and start fishing, and potentially add to the problem.
Peterson: The park service is pouring money into restoring trout at Solstice Creek. Fish biologists worry about the invaders – some studies indicate that trout that try to feed on the mudsnails starve. Sauvajot says it's tricky to figure out the problem's source – and its solution.
Sauvajot: Certainly the mudsnails are going to be competitors for the prey – so for the things steelhead would be eating – but we don't have a good handle on the extent to which that impact is going to occur and what it may do across the stream.
Peterson: Abramson says that's exactly why he'd like to see the warning signs on federal and state land sooner rather than later.
Abramson: We compromised on everybody's message, but they're not where there's easy access to the creek. How hard would it be to put one of those yellow signs up? Hell, I'll put one of them up for ya.
Peterson: A California parks spokeswoman said signs should be on state parkland. But the state has little money to manage nonnative species or to check park signs. So for now, disinfecting equipment – and scraping boots – is the first line of defense against the mudsnails.
[Sound of scraping boots]