NATURAL HISTORY
Science & Nature
DUNE GEOLOGY
The key ingredients needed to build a dune system include a source of sand, a shoreline perpendicular to the prevailing winds and a low landscape over which dunes can migrate. In addition, plant species that are adapted to survive the drying winds and shifting sands are needed to help shape and build the dunes. Here in the Humboldt Bay area, the Mad and the Eel rivers supply most of the sand. Winter storms flood these rivers and transport sand to the ocean. Sand is carried by currents along the coast and pushed up on to the beach by gentle summer waves. Once dry, the sand is moved by the prevailing summer winds from the northwest. This dynamic process has created of a variety of dune habitats within a narrow stretch of coastline.
The waveslope is the area of the beach that shows evidence of having been washed by waves during the last tidal cycle. Beachcombing here you can find everything from eelgrass, Pacific razor clam shells, sand dollars, to the carcass of a gray whale. This is also the feeding area for a number of shorebirds. They feed on small invertebrates in the sand and in the seaweeds washed on shore. The upper end of the waveslope is the strand. Here you may find plants such as sea rocket and native dune grass starting to colonize the bare sands.
The series of dunes and ridges paralleling the beach are collectively called the foredunes. In areas that are relatively undisturbed by invasive species, you can find a unique community of plants referred to as the dune mat. Here, a wide array of wildflowers adapted to the drying conditions of the dunes help stabilize the shifting sand. The dune mat is home to two federally listed endangered plant species, the Humboldt Bay wallflower and the beach layia. Take care to stay on the main trails through these areas.
Hollows/Swales form when the summer wind has removed the sand down to the water table, allowing water-loving plants to move in. During winter storms the water table rises and forms seasonal ponds in these areas. Tadpoles of the tree frog and the red-legged frog can be found here. Eventually, forests may develop in these areas.pacific
Few plants can survive the open sands of moving dunes. Look for mammal tracks of nocturnal animals like gray fox, skunk and raccoon crossing from the different areas. In some places, you can see that these moving dunes are slowly covering the dune forest. Large beach pine and Sitka spruce create an area that is surprisingly different and diverse.
Developed soils allow for thick plant growth, with huckleberry, silk tassel, red-flowering currant, salal. The forest is also home to many species of lichens, including puffy mats of reindeer lichens, more characteristic of northern forests.
Salt marshes and estuaries are recognized by biologists as among the most productive habitats in the world. The nutrient-rich waters form the basis of the salt marsh food chain. Plants such as pickleweed and salt grass are specially adapted to tolerating the salty conditions of a tidal area.
PHYSICAL GEOLOGY
HUMBOLDT BAY
Humboldt Bay, known to Wiyot People as Wigi, is the second largest enclosed bay in California. It is 14 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.
Photo by Gary Todoroff
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 nearshore 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: Spartina Invasion and Management.
SOLITARY BEES
Take a leisurely stroll through the local dunes on a warm day between April and September and your eyes will be met with a feast of wildflowers scattered across the sand in low-growing mats. Take a closer look, and you may notice a plethora of insects attending the blooms. Many insects, including beetles, flies, wasps, and bees, visit flowers to gather food in the form of pollen and nectar, and, while foraging, transfer pollen from one flower to another. This process, called pollination, results in fruit/seed production for the plant.
At least 67 percent of flowering plants today depend on insects for pollination. Bees in particular are important pollinators since their life history is closely linked to the flowers they service. Unlike wasps, which are carnivorous, bees rely on flower resources for all of their food, continuously foraging to fulfill both their own nutritional needs and those of their offspring.
If you are like most people, bee conjures up one of two images: the hard-working European honeybee (Apis mellifera), or its furry cousin, the bumblebee (Bombus spp.). However, most of the 20,000+ bee species in the world are solitary bees. In contrast to social bees, solitary bees have no colony or hive, no worker caste, and no stored resources. Instead, nests are the result of short-lived females working alone. During their 3-4 week lifespan, individual females provide 7-12 cells, each of which contains a single egg. These will then develop underground, and emerge the following spring to begin the cycle again.
There are about a dozen solitary bee species commonly found in our local dunes. Most are "generalists", visiting a wide variety of flowers to meet their nutritional needs. However, some species are "oligolectic". Bees of this type are picky about the plants they visit; they specialize in collecting pollen from only a few closely related plants. One of the few oligolectic species in the local dunes is the leaf-cutter bee (Megachile wheeleri). This bee forages exclusively on flowers in the aster family. This bee is abundant in late summer when dune goldenrod blooms abundantly.
In addition to floral resources, solitary bees in this system are also dependent on the dunes for nest sites and materials. In the early spring, you may notice "silver bees" (Emphoropsis miserabilis) swarming over the sand and among the beach pea flowers. These are males searching for newly emerged females to mate with. The females, once mated, will dig nests up to a meter in depth in the open sand in which to lay their eggs.
Other solitary bees nest in the cryptogamic mats (mossy crust) of the foredune and utilize specific plant materials to line their shallow nests. For example, a "wool-carder" bee (Anthidium palliventre), gathers plant hairs from beach buckwheat to line its nests. Check out the leaves of this plant beginning in April when Anthidium emerges, and you may notice bare spots where the "wool" has been removed, a sign that this bee is nesting nearby. Another bee, Megachile wheeleri, also nests in the cryptogamic mat, but this bee uses leaf pieces cut from dune goldenrod to line its nests. Look for clumps of goldenrod with "missing" leaf pieces in late summer and you’re likely to find this bee foraging on neighboring plants.
Ceratina acantha is a bee that’s easy to miss since it is quite un-bee-like in appearance: tiny (5-9mm), black, and hairless. This "carpenter" bee hollows out old dune goldenrod stems to use as nest sites. If you are lucky enough to spot an active nest, you will most likely see a tiny black face peering up at you from inside the hollow stem.
Aside from the important service they provide as pollinators, bees are fascinating creatures. The next time you’re out enjoying the floral display in the dunes, remember to keep an eye out for our local bees and give them a nod of "thanks" for the part they play in maintaining floral diversity.
WESTERN SNOWY PLOVER
The western snowy plover (snowy plover) is a small shorebird, approximately the size of a sparrow. The Pacific Coast population of the snowy plover is a distinct sub-population that is Federally listed as threatened under the Endangered Species Act (ESA). The snowy plover breeding season extends March through September. Locally, snowy plovers can be seen nesting and rearing their young along the sandy shores, estuaries, and the lower stretches of the Eel River. Nests usually contain three tiny eggs, which are camouflaged to look like sand and barely visible to even the well-trained eye. While a variety of pressures make survival difficult for these birds, four factors are the most significant within Recovery Unit 2 (Del Norte, Humboldt and Mendocino Counties).
Predators are the most significant factor affecting reproductive success of snowy plovers. Small mammals, such as fox and raccoon, and birds, particularly the common raven, prey on the eggs and chicks of snowy plovers. Occasionally, birds of prey also take adults decreasing the entire population.
Loss and degradation of breeding habitat is another factor affecting snowy plovers. They prefer open, sandy areas with sparse and low lying vegetation for nesting. Due in large part to the spread of introduced plant species, principally European beach grass, the number of suitable nesting areas has diminished.
Human activities including encounters with people, dogs, and vehicles as well as trash left behind can threaten the breeding success of snowy plovers. Energy is very important to this small bird. Every time humans, dogs, or other predators cause the birds to take flight or run away, they lose precious energy that is needed to maintain their nests. Just the presence of people and dogs in close proximity can cause adults to temporarily leave nests, which increases the chance of a predator finding the eggs, sand blowing over and covering the nest, or the eggs getting cold. Litter and food scraps left behind attract predators such as ravens and raccoons which could increase predation of eggs and chicks.
Inclement weather such as winter storms, river flooding, high tides, and strong winds can be detrimental to both breeding success and winter survival. Nests can be washed out during river flooding or covered by sand during strong winds. In the winter time, snowy plovers need all of their energy to stay warm and survive through extreme weather conditions.
FREQUENTLY ASKED QUESTIONS
Q: I see hundreds of snowy plovers running around on the waveslope why are they listed as threatened?
A: If you see hundreds, they are not snowy plovers. They are likely sanderlings, which look similar and are often mistaken for them. If the birds you see run in and out with the waves looking for food, they are not likely snowy plovers.
Q: What do snowy plovers eat?
A: Snowy plovers feed on invertebrates, such as beach hoppers, in piles of seaweed and debris along the high tide line. Snowy plovers glean insects from the surface versus probing under the sand like many other shorebirds.
Q: Why are there roped off areas on local beaches every summer?
A: This “symbolic” fencing helps alert beachgoers to the presence of snowy plovers and encourages them to avoid potential nesting and rearing habitat during the breeding season (March-September). At Little River State Beach, some fencing was put up to protect habitat restoration areas and the native plants.
Q: Are the conservation efforts working?
A: Recovery efforts throughout the western snowy plover range have proved effective at boosting populations. In Recovery Unit 2 (Del Norte, Humboldt, and Mendocino Counties), active protection of plovers began in 2000.This may seem like a long time, but it takes many, many years for populations of threatened and endangered species to rebound. There are many factors that influence population size, some of which we have no control over. For instance, the winter of 2005 and 2006 was particularly cold and wet and resulted in a drop in the adult population. Since then the population has been increasing.
Q: How does European beachgrass affect snowy plover breeding success?
A: European beachgrass, an exotic invasive, creates an impenetrable vegetative barrier for chicks between foraging and potential nesting habitats. Recent studies show European beachgrass communities have reduced invertebrate densities compared to native vegetation. Snowy plovers feed on invertebrates and tend to nest in open sandy areas with sparse or low lying vegetation. Native dune vegetation is more cryptic, low lying and provides good visibility for spotting approaching threats.
OTHER ENDANGERED SPECIES
BEACH LAYIA
The Humboldt County beaches and dunes are home to two federally listed endangered plant species; the Humboldt Bay wallflower and the beach layia. In addition, the western snowy plover, a small shorebird, is listed as a threatened species. The coastal habitats for these species are subjected to development pressures, recreational uses including off-highway vehicles, and encroachment by invasive plant species. The Endangered Species Act provides a mechanism to protect these species and the ecosystem upon which they depend. By conserving the dunes, we protect endangered species.
Humboldt Bay Wallflower (Erysimum menziesii eurekensii)
Humboldt County’s beaches and dunes are home to two federally listed endangered plant species: the Humboldt Bay wallflower and the beach layia. The Humboldt Bay wallflower is a subspecies of the Menzies wallflower and is unique to the Humboldt Bay dune system. The coastal habitats for this species and other native plants are subjected to development pressures, recreational uses including off-highway vehicles, and encroachment by invasive plant species. The Endangered Species Act provides a mechanism to protect these species and the ecosystem upon which they depend. By conserving the dunes, we protect endangered species.
Beach Layia (Layia carnosa)
Both the State of California and the U.S. Fish and Wildlife Service list this diminutive annual as endangered. Populations have been monitored since 1988. Since that time, densities have declined. Beach layia prefers open areas with sparse vegetation, and its decline coincides with the gradual and natural succession of vegetation in the dunes over time. When European beachgrass is removed and plant cover is lower, beach layia undergoes a temporary increase in density.
Other rare and endangered plants include:
Pink sand-verbena (Abronia umbellata spp. brevifolia)
Humboldt Bay owl’s-clover (Castilleja ambigua spp.humboldtiensis)
Point Reyes bird’s-beak (Cordylanthus maritimus spp. palustris)
dark-eyed gilia (Gilia millefoliata)
American glehnia (Glehnia littoralis ssp. leiocarpa)
western sand spurrey (Spergularia Canadensis spp. occidentalis)
sea-watch (Angelica lucida)
RESTORING THE DUNES
Dune systems depend on constant change. Invasive plants have upset the ecological balance by inhibiting sand movement, changing soil chemistry and crowding out native plants. Many invasive plants were first introduced to the dunes for the purpose of stabilizing the shifting sands in the early 1900’s.
The study of dune restoration first began at the Lanphere Dunes in the late 1970’s. Since then a lot has been learned about the practices of restoring dunes and how dunes react to the removal of invasive plants. Restoration of the dunes on the North Spit in Humboldt County focuses on hand removal of non-native, invasive plant species. With minimal disturbance to the land during restoration activities, the ecosystem is able to regenerate quickly. Native plants are able to increase in number and reclaim areas once invaded. This helps restore native biodiversity and return natural processes to the dune ecosystem.
You can learn more and get involved in restoring local dunes by participating in one of our volunteer restoration programs.
EUROPEAN BEACH GRASS
EUROPEAN BEACH GRASS
(Ammophila arenaria)
Native to Europe, this grass was planted along the north spit in 1901 to stabilize the sand along the railroad. The Latin name Ammophila means "sand-loving" as the grass thrives on being buried. This grass spreads by deep, tough, buried stems (rhizomes) and forms dense, continuous stands.
Dune Impacts – European beachgrass traps blowing sand and does not allow it to continue through the dunes system, causing dune stabilization. Sand movement is a critical part of the dynamic dune system and over stabilization creates an unnatural condition on the dunes. The thick stands that it forms crowds out native plants.
Control – European beachgrass is removed with hands and shovels. Although this is labor intensive, it is the most effective method locally. Because this grass is constantly being buried with sand its root systems grow deep in the sand. This makes it virtually impossible to remove the entire root. Portions of root remaining after initial removal efforts will re-sprout and will require 4-8 follow-up treatments before being starved of nutrients and die. Beachgrass is piled up and left to dry before being burned
ICE PLANT
(Carpobrotus chilensis and Carpobrotus edulis)
Iceplant is native to South Africa. It is believed that it was introduced to local dunes as early as the 1500’s for ship’s ballasts. The origin of Carpobrotus chilensis is not clearly understood, and some biologists believe it is native to California. This species is far less invasive than C. edulis. However, when C. chilensis hybridizes with C. edulis, it takes on more aggressive traits and should be controlled.
Dune Impacts - Iceplant is a succulent which stores water in swollen leave or stems enabling it to survive after being uprooted. It grows low to the ground and blankets the dunes, crowding out native plants, and stabilizing sand.
Control - Iceplant is easily controlled with manual removal. Large clones can be rolled up like a carpet with the roots being cut with shovels underneath as it is rolled. Small patches are piled up and left to dry. After a few months, piles are revisited and any pieces of the plant that are touching the ground and growing are removed and placed on the top of the pile until all of the pile is dead and dry.
YELLOW BUSH LUPINE
(Lupinus arboreus)
Yellow bush lupine is native to central California, but this species is not native to Humboldt County. There are two other species of lupine that are considered to be native here, but are smaller and less commonly seen on the dunes. Yellow bush lupine was introduced to the North Spit in the early 1900’s when the railroad was being used to transport rock to construct the north jetty. Five women were hired by the Army Corps of Engineers to plant the lupine seeds along the railroad to prevent unwanted sand burial. The seeds were obtained by the Presidio in San Francisco.
Dune Impacts – Yellow bush lupine is a large shrub that creates a new microclimate by providing shade and moisture to surrounding plants. The roots have nodules which contain nitrogen-fixing bacteria that increase nutrients and organic matter in the sand, creating a condition where other weedy plants can become established.
Control – Small yellow bush lupines are removed by physically pulling up the entire plant, including the deep taproot. Larger bushes are removed using an axe to chop the plant off at the base. Shrubs are then piled, dried and burned. Lupines have long-lasting seed banks, so removal efforts must be continuous as new plants will emerge from seeds that have previously been dispersed.
FURTHER READINGS
Frequently Asked Questions About Restoration
Pickart, A. 2008. Restoring the Grasslands of Northern California’s Coastal Dunes. Grasslands. Published by the California Native Grasslands Association. Vol XVII, No. 1.
Pickart, A.J., and J.O. Sawyer. 1998. Ecology and Restoration of Northern California Coastal Dunes. California Native Plant Society, Sacramento, CA.
STEWARDING OUR COASTAL DUNES
Carol Vander Meer
05/21/2013
You may know Friends of the Dunes for our Annual Sand Sculpture Festival, or our school programs that have introduced thousands of Humboldt County students to the coastal dunes, or maybe you know us as the group that opened up the Humboldt Coastal Nature Center. We are all of those things and more, including being a group working to involve the community in restoring the natural diversity of coastal environments by removing invasive, non-native plants like European beachgrass
Friends of the Dunes has been involving the community in coastal conservation for over 30 years. We are an active member of the Dunes Cooperative that facilitates coordinated ecosystem management of coastal dune environments through the collaboration of local land managers. Our staff and Board of Directors have expertise in natural resource management, geology/geomorphology, wildlife biology, plant ecology, and education.
There have been some misconceptions circulated lately about coastal restoration activities and their impacts. We would like to offer some insight about the process of restoration, how it helps restore natural diversity and its relationship to coastal processes. Friends of the Dunes works with experts in coastal land management, scientists working in coastal processes and members of the local community to support the restoration of resilient coastal ecosystems, while also accounting for the needs of neighboring communities.
The goal of dune restoration is to restore the natural diversity of plants and animals to the dunes and help return, where appropriate, the natural processes that sustain dune ecosystems. It is the varied conditions caused by a constantly shifting, changing landscape that creates the unique, diverse habitats for plants and animals that we enjoy today. Dunes are by nature moving and dynamic. In some places, forests become covered with sand, while in other areas new forests develop. Open sand is often quickly colonized by early successional plants. Wetlands are formed when dune swales are carved out by the wind down to the water table, but their locations shift and change as sands move. It is an active cycle of processes that creates and sustains these shifting habitats and biological communities.
Our dunes are wide and broad with a relatively low foredune, a broad, undulating expanse of mid-dunes and much higher forested back dunes. Unlike some places along the Oregon coast, where houses are built right on the coastline, most buildings and homes along our coast are at least a quarter of a mile or more from the beach, and were built in stable, forested back dunes. This makes it possible to restore some dune processes, closer to the ocean, without threatening property and homes. In areas near communities or infrastructure, we are adapting our approaches to restoration to include plantings of native dune plants, which reduces sand movement.
We are open to dialogue about how to incorporate the best science available to ensure that the beauty and dynamic nature of the dunes is enjoyed today and for generations to come. How to adapt to ongoing climate change is one of the important questions in coastal dune management today.
Ongoing studies are underway that will help us to predict how our dunes will change as sea levels rise, and how vegetation may respond to these changes. Andrea Pickart, an ecologist for Humboldt Bay National Wildlife Refuge, recently wrote in an article in our newsletter, Dunesberry:
"In some ways, coastal dunes are one of the more resilient ecosystems with respect to climate change. Located at the boundary zone between marine and terrestrial ecosystems, they are dynamic systems that have historically undergone constant, albeit gradual change in response to climate and related sea level changes. From this long history of change, we know that dunes have the capacity to migrate and equilibrate with new sea levels."
Friends of the Dunes will continue to work with scientists and coastal land managers to develop and implement the best dune management and restoration practices for our coastal areas. We will further the work of coastal conservation by sharing the beauty of our coast to students, visitors and community members through educational opportunities, restoration efforts and conservation projects. We do this because we believe that connecting people to nature is an essential part of conserving and protecting the ecosystems which sustain us.