Pescadero Marsh

• Category: Marine and Oceanic Biomes.
• Geographic Location: North America.
• Summary: This marsh in northern California is an important stopover and nesting ground for migrating waterbirds, and a critical breeding and nursery habitat for many endangered species of fish, amphibians, and reptiles.

Located just 50 miles (80 kilometers) south of San Francisco, California, the Pescadero Marsh biome is an estuary that connects the redwood forests of the Santa Cruz Mountains to the kelp forests of the Pacific Ocean. The upper Pescadero watershed is extensively wooded, including willow-alder riparian corridors above the estuary. The marsh itself is not large, at only 340 acres (138 hectares), but it is home to at least six threatened or endangered species, including steelhead trout, coho salmon, the tidewater goby, San Francisco garter snake, and the California red-legged frog. During the winter, more than 200 species of birds use the marsh to nest and feed during their annual migrations.

Pescadero Marsh is located at the confluence of two streams, Pescadero Creek and Butano Creek, which together drain more than 80 square miles (200 square kilometers) of the Santa Cruz Mountains. As the largest watershed between the Golden Gate Bridge and the coastal town of Santa Cruz, the Pescadero-Butano watershed and Pescadero Marsh represent an oasis of critical spawning and nursery habitat for fish, amphibians, reptiles, and shellfish along a well-developed coastline. It supports one of the largest remaining runs of steelhead within the northern California region; it also supported a large coho salmon run as recently as the late 1960s, although few if any coho have returned to spawn in recent years.

The Pescadero watershed and marsh typically has cool, wet winters and mild, mostly dry summers. Fog and overcast skies are common, particularly during the summer months, because of the cold, adjacent Pacific Ocean. January is the coolest month, with an average maximum of 60 degrees F (16 degrees C) and an average minimum of 40 degrees F (4 degrees C). September is the warmest month, with an average maximum of 72 degrees F (22 degrees C) and an average minimum of 49 degrees F (9 degrees C). Winter temperatures seldom drop below freezing, so there is rarely snow. Average annual precipitation is approximately 30 inches (75 centimeters).

Human Impact

Humans have been modifying and exploiting the marsh since before Europeans arrived in North America. The Portola Expedition, the first Spanish exploration of the California coast, found the area inhabited by the Ohlone people, who burned the grassy meadows of the marshes to stimulate growth of the grasses that they depended on for food. Throughout the 1800s, the foothills above the marsh were used for cattle ranching and farming.

Logging of the massive redwood trees found in the mountains began in the 1850s and continued for the next 100 years. Occasionally, the sawdust released from sawmills into the streams would cause the waters downstream to become toxic to people and to fish. In the 1870s, lawsuits were brought against the sawmills to stop the practice, and in 1877, fish stocking began in Pescadero and Butano Creeks as an effort to rebuild the trout population.

During the 1920s and 1930s, farmers began to construct extensive levees along the creeks and upper marsh to divert water for crops. Also during this time, a bridge was built across the marsh as part of the construction of California Highway 1. The combined effects of hundreds of years of human activity on the marsh from fire, ranching, farming, logging upstream, and channelization of the creeks downstream has been to increase sedimentation in the marsh and degrade the suitability of the habitat for native species.

A common feature of many coastal estuaries is the formation of a seasonal sandbar across the mouth of the estuary. Behind the sandbar, the marsh gradually transforms into a freshwater lagoon. The formation of the lagoon here is critical to the growth of juvenile salmon and trout that live in the marsh. However, because of the increased sediment load in the marsh and diversions of water for crops, the lagoon may form too late in the season or be too shallow to function as nursery habitat for the fish of the marsh.

Runoff (mainly nitrates and phosphates) in the marsh waters from fertilizers used by farmers upstream eventually filter down into this area, causing it to become eutrophic, or overloaded with nutrients; the high levels cause algal blooms that reduce the oxygen in the water and increase decomposition in the sediments. Sometime in the fall, the sandbar barrier is breached, and the marsh transforms again from a freshwater lagoon back into a tidal estuary. Since 1995, the breaching of the sandbar has coincided with large fish kills in the marsh. Water low in dissolved oxygen and high in hydrogen sulfide is released during the flushing of the lagoon; this makes the marsh waters too toxic for fish to live. Native species populations in the wetland, for this and related reasons, are at critically low levels.

Climate change caused by human activity looms over the marsh and its effects are not fully understood yet. Concerns about drought, rising sea levels, extreme flooding, and extreme tidal events linger in the background. The California Department of Fish and Wildlife is taking steps to prepare the region for future changes and make the habitat climate resilient. One such project aims at restoring the natural process to the Pescadero Creek Lagoon.

Conservation

Efforts have been made to alleviate some of the stressors placed on the watershed and the marsh. The cessation of sawdust dumping by the sawmills and the eventual protection of the old-growth redwood forest in the mountains of Butano and Big Basin Redwoods State Parks were vital to protecting the watershed downstream. In the late 1930s, California golden beavers were reintroduced to the upper watershed to reduce sedimentation downstream. Beavers can dramatically modify watersheds by holding back water and debris with their dams. Their reintroduction, following extirpation by fur traders, has been credited with reducing sediment flow downstream and represents a natural method of watershed protection.

In 2004, an extensive assessment of the Pescadero-Butano watershed, including the Pescadero Marsh, was conducted. This assessment was performed to evaluate the health of the entire watershed and to determine how best to manage the watershed and marsh to best support the critically endangered runs of steelhead trout and coho salmon into the future. The problems facing Pescadero Marsh are the same faced by coastal estuaries around the world.

Logging of upstream forests increases sediment flow downstream, and farming and ranching in the watershed increase the amount of nutrients in the estuary waters. Encroaching development encourages channelization and reduces seasonal flooding events, which actually may alleviate some effects of sedimentation and eutrophication. Butano Creek is presently identified as a California Critical Coastal Area, as it flows into a Marine Protected Area (Pescadero Marsh Natural Preserve). However, flooding and erosion already pose a threat to human and wildlife communities along the California coast, and there is strong evidence that these risks will increase in the future due to global climate change. California coastal areas are already vulnerable to storms, extreme high tides, and rising sea levels. Even with protection, the future of bay and wetland regions remains uncertain.

Bibliography

Bay Area Open Space Council. The Conservation Lands Network: San Francisco Bay Area Upland Habitat Goals Project Report. Berkeley, CA: Bay Area Open Space Council, 2011.

 “California Environmental Quality Act Statutory Exemptions for Restoration Projects Concurrence No. 21080.56-2024-049-R3.” California Fish and Wildlife, 14 Feb. 2024, nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=220052&inline. Accessed 26 Nov. 2024.

Heberger, Matthew, Heather Cooley, Pablo Herrera, Peter H. Gleick, and Eli Moore, eds. The Impacts of Sea-Level Rise on the California Coast. Oakland, CA: Climate Change Center—Pacific Institute, May, 2009.

Monterey Bay National Marine Sanctuary Foundation. “Pescadero-Butano Watershed Assessment.” Environmental Science Associates, montereybay.noaa.gov/resourcepro/reports/sedrep/welcome.html. Accessed 26 Nov. 2024.