Humboldt Bay

Physical Geography

Humboldt Bay, known to Wiyot People as Wigi, is the second largest enclosed bay in California. It is14 miles long and 4.5 miles across at its widest point. The channel, approximately 30 feet deep, is located near the north end of the South Bay and connects the bay to the ocean providing daily interchanges of seawater. The bay consists of two wide but shallow northern and southern arms connected by a relatively narrow channel.

Arcata Bay, also called North Bay, is the larger of the two bay segments and covers a surface area of about 8,000 acres. Most of Arcata Bay is extremely shallow and about 4,500 acres of mudflats are exposed at low tide. The shallow mudflats are traversed with deeper channels formed by tributaries and erosion from tidal drainage. The South Bay is about 4,600 acres in size and is similar to Arcata Bay in character. It is also mostly shallow, and 2,400 acres of mudflats are exposed at low tide. In addition to abundant mudflats, lush eelgrass beds are located throughout the South Bay.

Humboldt Bay is an estuary, which is an area where saltwater and freshwater come together and mix. The bay receives most of its freshwater as runoff from a drainage area of approximately 288 square miles surrounding the Bay. The main tributary streams are: Jacoby Creek, Freshwater Creek, Elk River, and Salmon Creek. Many smaller streams also enter the Bay directly or by way of one of its tributary sloughs.

Ecology

The two main habitats of the Humboldt Bay are mudflats and eelgrass beds. Eelgrass (Zostera marina) is not an alga but an angiosperm (flowering plant). It grows mostly in shallow water bays and is the main food source for black brant and other waterfowl species. Eelgrass beds also serve as important habitat and nursery areas for many species, a lot of which are important for sport and commercial fisheries. Some species that use eelgrass beds during part of their life include lingcod, Dungeness crab, halibut, Cabazon, English sole, Pacific herring, and several species of near shore rock fish. There are also many animals that spend their entire life in the eelgrass such as bay pipefish, nudibranchs and sea hares. The bay is also home to some marine predators, including brown smooth hounds, leopard sharks, and seven gill sharks.

The intertidal mudflats of the bay are fully exposed at low tide, and entirely covered by water at high tide. Plant life on the mudflats consists of eelgrass, and several species of algae including sea lettuce (Ulva spp.), rockweed (Fucus sp.), and polysiphonia (a red alga). Invertebrates are abundant in the mudflats and many birds depend on them food. Most invertebrates occur in the top 6 inches of the mud with approximately 97% being found in the upper 2 inches. The species and numbers of invertebrates present are determined by the sediment composition and location in relation to tidal submergence time. Some invertebrates that burrow in the mudflats include polycheate worms, clams, ghost shrimp, and fat innkeeper worms.

The mud of the bay has a rotten egg odor, and that the yellow-brown color of the mud surface differs from the blackish color of the mud underneath. Beneath the thin surface layer, little oxygen can penetrate and bacterial respiration is anaerobic. The by-product, hydrogen sulfide, smells like rotten eggs. The hydrogen sulfide reacts with iron sulfide to produce hematite, which is yellow-brown.

Invasive dense-flowered cordgrass (Spartina densiflora) has infested an estimated 90% of salt marshes in Humboldt Bay and the adjacent Eel and Mad River estuaries. The invasion of Spartina threatens the natural diversity and structure of salt marshes in Humboldt Bay as well as other estuaries along the west coast. You can read more about Spartina and salt marsh ecology, restoration methods, the status of Humboldt Bay National Wildlife Refuge's two-year refuge eradication project, and links to other west coast and international Spartina eradication efforts at: www.fws.gov/humboldtbay/spartina.html .

For more information about Bays and Estuaries see: www.dfg.ca.gov/ocal/archives/bays_estuaries_nd02.pdf.