At the heart of Monterey Bay, where the submarine canyon meets the shore, is one of the Nation’s most valuable, and most fragile, natural resources. The tidal estuary, named Elkhorn Slough, is an immensely rich biological area. It contains a high number of interdependent aquatic and upland habitats, and a diversity of species that might be the highest in California for a watershed of its size. The estuary contains California’s largest remaining tidal salt marsh outside of San Francisco Bay. Because such estuaries are in rapid decline, it has a disproportionate number of rare, threatened, and endangered species. Among them are the brown pelican, California least tern, Santa Cruz long-toed salamander, southern sea otter, American peregrine falcon, and California red-legged frog. The estuary and its wetlands are a resting spot for more than 200 migrating bird species.
Thousands of years before Spanish and Mexican settlers arrived, Ohlone Indian villages thrived in this rich, mild, environment. Indian middens around the estuary are full of the shells of marine invertebrates and the bones of birds and mammals.
The California Department of Fish and Wildlife has designated parts of Elkhorn Slough as a State Ecological Reserve and as a Wildlife Management Area, including the Elkhorn Slough State Marine Conservation Area, and the Moro Cojo State Marine Reserve. These Marine Protected Areas are designed to protect the estuary’s natural structure and food web, to support its high level of biodiversity. The federal government has included the slough’s tidal waters within the Monterey Bay National Marine Sanctuary, and has established a National Estuarine Research Reserve on its eastern shore. The National Audubon Society includes the estuary in its Globally Important Bird Areas and the Western Hemisphere Shorebird Reserve Network designated it a Site of Regional Importance.
The Elkhorn Slough National Estuarine Research Reserve (ESNERR) was established as field laboratory for scientific research and estuarine education. A visitor center invites tourists to explore the estuary, and docent-led hikes take young students out to learn about the beauty and importance of this natural resource. Throughout the reserve are five miles of trails that meander through beautiful oak woodlands, tidal creeks, and freshwater marshes.
Unfortunately, the Elkhorn Slough Tidal Estuary and its resident species are threatened by invasive species, erosion, and industrial pollution. The slough’s sediments act as a sink for bioaccumulative deposits of heavy metals, and strong winds and tidal currents continually re-suspend and redeposit these metals. Heavy agricultural use of adjacent lands causes erosion, filling wetlands with sediment and industrial pesticides. Toxic chemicals are concentrated in the estuary’s food web as toxic metals, and other contaminants absorbed by plankton, are consumed by shellfish, fish birds, and marine mammals, and humans. The human health consequences can disproportionately harm minority communities, who typically eat a greater than average amount of fish, such as the leopard sharks and bat rays that frequent the estuary.
Southern sea otters use the estuary and its wetlands heavily. The Yampah Marsh portion of estuary has the highest density of sea otter mothers with pups anywhere in the range of these iconic animals, who are struggling to recover from near extinction. Otter pups are particularly susceptible to the harmful effects of bioaccumulative toxic substances, as mothers offload contaminants in breast milk when they first give birth. First-born pups are particularly vulnerable to high levels of contaminants. Harbor seals also haul out in the estuary and are potentially affected in the same manner as sea otters.
Several fish species – such as English sole, top smelt, anchovies, sculpin, and leopard sharks – use the Slough as a nursery, and fish can be vulnerable to contaminants. These are important forage fish for birds and other animals, so toxic effects reverberate up the food web.
Stormwater contaminated with metals and other pollutants also harms the special aesthetic and recreational significance that the Elkhorn Slough has for visitors and the surrounding communities. Aquatic sports are very popular in the Monterey Bay Area, and the Elkhorn Slough Estuary is heavily used by kayakers, canoers, swimmers, shellfish harvesters, bird watchers, hikers, and recreational and subsistence anglers. The public’s high use of the estuary for water contact sports exposes many people to toxic metals and other contaminants present in stormwater runoff. Non-contact recreational and aesthetic opportunities, such as wildlife observation, also are damaged by contaminants discharged to the estuary.