By Liam Zarri, UCSC, Graduate Student, Ecology & Evolutionary Biology Department
Consider taking a stroll along the Santa Cruz Riverwalk this month, as you will witness a seasonal phenomenon. Walking downstream from the Tannery Arts Center, past downtown Santa Cruz, the river begins to grow into a lagoon. Is that the tide, pushing the water up? No, a sand bar has formed where the river meets the sea and trapped river water in a brackish (mix of freshwater and saltwater) lagoon.
These bar-built estuaries (where the river meets the ocean) are common and also form at creeks such as Lagunas, Scotts and Waddell. The largest coastal lagoons between Santa Cruz and San Francisco are Pescadero Creek and the San Lorenzo River. To learn more about estuaries, I spoke with Ben Wasserman, a PhD student at UC Santa Cruz:
“Although we understand the basic seasonal cycle of breaching in the winter and lagoon formation during the summer, a lot differs from year to year: rain and surf conditions have a major impact on what shape the bar takes, how high the water backs up behind it and how it eventually breaches. We don’t yet fully understand what impacts different types of water years will have on tidewater goby populations.”
Figure 1. Ben Wasserman & Alexandra Repetto (UC Santa Cruz undergraduate) pulling a seine net for lagoon fishes.
As you continue to walk past the Broadway bridge, the lagoon grows until it reaches the levee on both sides. The brackish lagoon supports fish such as threespine stickleback, sculpins, salmonids, and the endangered tidewater goby. The tidewater goby (Eucyclogobius newberryi) is a California endemic (occurs only here) and an annual species (living for only 1 year) which reaches 4-5 cm in size and consumes invertebrates. This goby is unique in that it exhibits sex-role reversal; the females compete for male mates (Swenson 1996). After courtship and mating, the male builds a burrow in sandy substrate and cares for the eggs over 9-11 days while fasting in the burrow. The young gobies emerge and spend the summer feeding and growing in the estuary, and may be flushed out to sea with the natural breaching of the lagoon in the winter. If you enjoy spending time by local estuaries, you have this diminutive goby to thank; its listing on the Endangered Species Act protects many estuaries from development.
Figure 2 The tidewater goby. Note the mottled skin which allows it to blend into its environment. Picture courtesy of Ben Wasserman.
As your walk culminates in the juxtaposition of the roaring Giant Dipper and Main Beach, the sandbar that forms the unique lagoon habitat comes into view. Unfortunately, the spreading water can seep under buildings, into resident’s basements, downtown businesses and the Boardwalk, resulting in costly water damage. If too much seepage occurs, authorities will breach the sandbar to prevent further damage, whilst stretching a net to save fish such as the tidewater goby. If the young gobies were to reach the sea, they would likely perish due to high salinity or ocean predators. As a more long term solution, the City intends to build a culvert pipe which will allow the lagoon to drain if it gets too deep and before seepage occurs. As you take in the view of the Pacific Ocean at the end of your walk, ponder the significance of this management balance which allows cities and ecosystems to peacefully coincide.
Questions? Email Liam at email@example.com or visit Liam’s website to learn more about his work.
Swenson, R.O. and McCray, A.T., 1996. Feeding ecology of the tidewater goby. Transactions of the American Fisheries Society, 125(6), pp.956-970.
A tidewater goby is caught as part of a survey in the Pescadero Lagoon and watershed. Prior to the lagoon breach, the U.S. Fish and Wildlife Service went out to survey for the endangered Tidewater goby. Photo Credit SarahSwenty/USFWS