Birds & Science
Functions and Values of Coastal Wetlands
- Provide open space and recreation
- Provide natural flood control
- Purify the water
- Produce oxygen
- Are outdoor laboratories for scientists and educators
- Provide sediment traps and erosion control
- Serve as nurseries for marine fishes
- Provide homes for endangered species
- Provide habitat for migrating, wintering and breeding birds
- Serve as repositories for native plants and animals
Bolsa Chica is an Ecosystem
What is an ecosystem? An ecosystem is a unit of the environment in which living and nonliving components interact. Bolsa Chica may be called an ecosystem where saltwater from the ocean and freshwater from land meet and mix. A clear understanding of the nature of the interactions between living things and nonliving things at Bolsa Chica would be very helpful in determining how best to protect it and maintain it in the future.
The prominent nonliving parts of the Bolsa Chica are the sun, saltwater, freshwater, air and mud. The mud is composed of detritus, or decomposed organic matter, and soil carried into the marsh by rainfall draining off the upland slopes.
The living parts of the marsh include birds, fish, invertebrates, and plants (including plankton). Of these components, the plants are the most important to the ecosystem. They are called the primary producers because they can make their own food from carbon dioxide and water, using the sun’s energy. This process is called photosynthesis, and it is essential to the continued existence of the marsh. One important by-product of photosynthesis is oxygen.
Bolsa Chica: A Tidal Salt Marsh
What is a tidal salt marsh? It is a community of plants and animals that are tolerant of wet, saline conditions. This community is a transition between land and ocean systems, and thus contains aspects of both. The soil is saturated with water or covered by shallow water, and this water has a salinity level generally between that of freshwater and saltwater. The level of the water in a tidal salt marsh fluctuates daily due to tidal action.
The tidal salt marsh has a complex zonation of plants and animals. The lower and upper limits of the marsh are set by the tide range: the high marsh is flooded irregularly and the low marsh (including mudflats) is flooded at least daily. Narrow subtidal channels serve as conduits between the salt marsh and the adjacent ocean. Each of these zones is a distinct habitat favored by different groups of plants and animals.
Bolsa Chica is dominated by the high marsh, but it also has extensive mudflats, with some channels and open water. Another habitat found at the Bolsa Chica is the salt flat. The salt flats have no vegetation, and contain water only after rains. These interim ponds are quite salty and support many insect larvae. Shorebirds can feed on these larvae without competition from fish.
Zonation depends on several factors: two important ones are salinity and nutrient availability. Salinity changes depending on these conditions:
1. frequency of tidal inundation
3. tidal creeks and drainage
4. soil texture
6. depth of water table
7. freshwater inflow
Nutrient availability varies considerably, especially the supply of usable nitrogen and phosphorous. Often there is not enough oxygen present in marsh soils to combine into useful nitrates and phosphates.
Bolsa Chica Wetlands Through the Changing Seasons
In Spring at the Bolsa Chica Wetlands, the days and the water become warm and tidal circulation is low. “Neap tides” are prevalent, with a small tidal range between the high and low tides. Two kinds of green algae grow and become dominant in the water during these months: stringy Enteromorpha and flat Sea Lettuce. Marsh plants such as Pickleweed, Saltgrass, Shoregrass and Jaumea begin flowering, and the sand dune plants bloom from late March through summer.
Brown Sea Hares, Horn Snails and Shore Crabs are easily seen grazing the algae in the waters below and the walkbridge. Snakes and lizards come out of hibernation. Side-blotched and Western Lizards sun themselves on the trails.
Sightings decrease of winter ducks and shorebirds, with ducks leaving earlier than the shorebirds for their northern breeding grounds. Occasionally these birds show courtship behavior before they leave, such as the Western Grebe which “runs” across the surface of the water. The summer migrants (terns) begin arriving in April from their southern wintering grounds. Throughout the spring, the Elegant Terns perform aerial courtship displays and male endangered Least Terns offer fish to prospective mates. Male Red-wing Blackbirds cling to the cattails, and defend their territory by calling and flashing their red wing patches.
In Summer, the warm dry days cause a decline in the green algae. As the algae decomposes, it provides tiny particles of food (“detritus”) for filter-feeding animals such as Clams, Sea Squirts, and Sponges. Filamentous Blue-green Algae dominates in summer, forming microscopic tufts or mats on the mudflats and plant stems. Most of the marsh plants are flowering now, including Sea Lavender which sends up tall stalks of tiny purplish-white flowers.
“Spring tides” occur between May and June, with great ranges between the high and low tides. The underwater life is easily seen. Stingrays enter Bolsa Chica waters looking for clams and crabs. In some years, large populations of Common Jellyfish are pushed by the tides to the edges of the marsh.
Nesting Elegant and Caspian Terns cover Tern Island south of the walkbridge and in late summer Black Skimmers join them. Black-necked Stilts and Avocets loudly defend their chicks near the parking lot and Rabbit Island. By late summer, these chicks are grown and nearly identical in appearance to the adults.
In the Fall, dry wind, high evaporation rates and a lack of “Spring tides” create drought stress in the upper marsh habitats and saltflats. Trash accumulates in the wetlands, blown over Pacific Coast Highway from the summer beach-goers.
Most marsh plants cease flowering by late fall except for Cordgrass and Sea Lavender. The Pickleweed begins to turn red or pink; later the ends of the stems dry up and break off, returning stored salt to the soil.
The terns and swallows which were present in summer depart the Bolsa Chica, migrating south for the winter. The winter birds begin arriving from the north in small numbers, with shorebirds arriving earlier than the ducks. Some of the shorebirds may still show portions of their summer “breeding” colors, such as the Black-bellied Plover (pictured above) and other species of shorebirds.
In Winter, storms provide freshwater which decreases the salinity (“saltiness”) of the soil. Storm runoff from inland cities comes down the Wintersburg Flood Control Channel, which empties near the tidegates and carries unwanted trash into the wetlands along with the freshwater. “Spring tides” occur again between December and February, with saltwater reaching the upper portions of the marsh. In some years, the high tides on the ocean side combine with heavy rains to flood Pacific Coast Highway and cause its closure.
The water is cool, and thus primary productivity of the plants is low. However, the decreased salinity helps Pickleweed seeds germinate, and large expanses of Pickleweed follow wet winters. No marsh plants are in flower during these months, although Heliotrope and Telegraph Weed bloom late into winter.
Winter brings the highest concentrations of ducks, grebes and shorebirds which may be seen resting and feeding in the wetlands. Flocks of “diving ducks” such as Surf Scoter, Lesser Scaup, Bufflehead, Ruddy Duck float in the middle of the bays, while Marbled Godwits, Willets, Dowitchers, Dunlin, and Western Sandpipers congregate on the shores. “Dabbling ducks” include Northern Pintail, American Wigeon, and Blue-winged Teal. Several species of Loons and Western Grebes chase the abundant fish population.
The resident Belding’s Savannah Sparrow begins staking out territories and is most visible as it perches on top of the pickleweed. Spring approaches.