Robert Leidy and Stephanie Carlson show the way along the stony bed of Coyote Creek. Even after last winter’s record-setting rains, much of it is bone-dry in late September. The main waterway in Morgan Hill’s 87,000-acre Henry W. Coe State Park has been reduced to a series of rapidly drying pools.
But as Leidy, an Environmental Protection Agency ecologist, and Carlson, a UC Berkeley professor and fish ecologist, have learned through research along a 2.5-mile stretch of Coyote Creek over the last four summers, the protected waterway’s extreme annual swings above Coyote Dam — from flood to fragmentation and back — also make it a bastion of native biodiversity. “It’s almost a reference state,” Leidy says of the creek’s undisturbed condition.
There’s a common perception in California that more water is always better for fish. Yet many native species possess traits that allow them to persist through harsh, dry summers and cyclical drought. Over the long run, summer releases from reservoirs and urban runoff can harm local fish by laying out a welcome mat for non-native species adapted to perennial flows, Leidy says. “In areas where streams have been altered by humans, where the natural hydrograph has changed, that’s where you see invasives take a foothold.”
Coyote Creek’s strictly seasonal flows, and those of other naturally intermittent streams in the state, by contrast, are so extreme in the winter and so sparse in the summer that non-natives simply can’t cope. “It’s physically too much for them, and they just can’t get established,” Leidy says.
What’s more, intermittent streams that fragment or “disconnect” during summer offer both creek and pond habitat, likely supporting a greater diversity of aquatic and terrestrial species than even a naturally perennial stream.
Leidy and Carlson’s latest visit to Coyote Creek is part of an ongoing effort they launched in 2014 with former Berkeley postdoctoral scholar Michael Bogan to better describe and quantify summer intermittency along Coyote Creek and its relationship with the distribution of aquatic species. Before heading to the University of Arizona, where he’s now an assistant professor, Bogan identified some 170 species of invertebrates in the creek’s remnant pools, seeps, and springs — predominately insects but also including sponges and the imperiled California floater freshwater mussel.
Today’s task: sampling fish populations in a series of larger pools along the mostly still creek. Wearing waders, Leidy and Carlson enter a waist-deep pool with a fifteen-foot seine, which looks something like a heavy-duty badminton net. They begin pulling it slowly through the water toward a sandbar on the other side where Pablo Rodriguez-Lozano, a postdoctoral researcher in Carlson’s lab, and Megan Fitzgerald, an EPA biologist, await with half-full buckets of water at the ready. The seine comes ashore wiggling with dozens of tiny fish, mostly chunky California roach and torpedo-shaped Sacramento pikeminnow, and all four researchers set to quickly picking them up with their fingers, one-by-one, and dropping them in the buckets.
Over the course of the summer Rodriguez-Lozano has led similar surveys up and down Coyote Creek, sampling fish every month in ten predetermined pools of various sizes to study the relationship between fish size and pool connectivity. Preliminary results show that fish condition (a measure of the relationship between weight and length) does decrease, particularly for roach and sculpin, once pools disconnect, suggesting that the harsh conditions stress our native species just as they support them.As Rodriguez-Lozano and Fitzgerald begin the time-consuming task of recording each fish’s species, length, and weight, Leidy and Carlson return to the pool with hand nets to search for riffle sculpin, which tend to live along stream banks and are difficult to catch with a seine.
Rodriguez-Lozano’s study builds on Leidy and Carlson’s larger long-term effort to map and measure stream connectivity here during the summer and fall, from May until the first significant rain, to better understand patterns of biodiversity and population persistence in drying pools. Now in its fourth year and planned to continue for many more, the project already includes a historic drought and a historic deluge — but no “normal” years, which both complicates and enriches the dataset.
Last summer was a different story, with the creek contracting only 35 percent by November after a soaking-wet winter. Most species appeared to appreciate or at least tolerate the extra water, Carlson says — apart from the Sacramento sucker, whose numbers were way down. She suspects the fish, which tends to be quite tolerant, was hurt by unusually high flows during winter storms.
Other research projects led by Berkeley students and postdocs at Coyote Creek under the tutelage of Carlson and Leidy seek to understand how intermittent streams help feed terrestrial organisms like racoons, snakes, and birds over the course of the summer, as pools get smaller and fish become more vulnerable to predation, why “sanctuary” pools exist where they do, including the influence of large boulders from landslides on pool persistence, and how long Pacific brook lamprey can survive in the gravel of pools whose surface water has evaporated.
Although findings to date are limited, the message behind all this work is that organisms native to intermittent streams, in California and around the world, are well suited to harsh conditions and severe seasonal swings — a fact that could have implications for conservation and land management in the coming decades. “With climate change, they’ll be more threatened,” Leidy says. “But they also may be more resistant, as we’ve seen in Coyote Creek where organisms persist in pools that are somewhat decoupled from annual rainfall. These could be important refuges to protect biodiversity.” NS