Docent Training 2006-2007
Bolinas Lagoon is a small, shallow estuary located directly along the San Andreas Fault, 15 miles northwest of the Golden Gate Bridge.
Covering less than 1500 acres, the triangular lagoon is 3.5 miles long and a mile across at its widest. It is protected from the Pacific Ocean by a long spit which terminates at the lagoon's mouth, its lifeline to the sea. Like an enormous aquatic lung, the lagoon breathes in sea water on rising tides, and exhales a mixture of fresh and sea water at low tides. An average of three million cubic yards of water are exchanged between the lagoon and the ocean with each tide.
Most estuaries are born when a river valley floods during a period of rising sea levels. Their life span is usually determined by the balance of two opposing processes: sedimentation and scouring. Due to its location along an active fault, Bolinas Lagoon is unusual in being influenced by a third process as well, tectonic subsidence, which assists scouring to counteract the force of sedimentation.
Here’s a view from where we just were looking back at Picher Canyon and Clem Miller
Most of CA coastal wetlands are estuarine salt marshes with associated tidal channels and mudflats.
Wetlands are unique biological communities characterized by both aquatic and terrestrial features.
Estuaries and coastal wetlands are some of most impacted ecosystems on the planet.
Since the 1850’s 90% of California’s original coastal wetland acreage has disappeared.
Legislative protection was not enacted until the 1960s and 1970s.
A healthy salt marsh provides 10 times more oxygen and corresponding biomass per acre as a wheat field.
LagoonLagoon versus EstuaryEstuary?
• Lagoon: A shallow body of water that does not receive significant freshwater inflow and that is separated from the open ocean by a barrier island, coral reef, sandbar.
• Estuary: A partially enclosed body of water where freshwater is mixed with saltwater [ETYMOLOGY: 16th Century: from Latin aestuarium marsh, channel, from aestus tide, billowing movement, related to aestas summer]
Bolinas Lagoon is essentially an estuary. It is a Ramsar Wetland of International Importance. One of only 17 in the United States.
What’s so great about estuaries? They • are nursery grounds for fish and some invertebrates • extremely productive • are stopovers for migrating birds (key component of Pacific Flyway) • assist in water purification by filtering and assimilating pollutants from outfalls and runoff • provide flood control services and buffer effects of storms, reducing shoreline erosion • are important players in nutrient recycling; export nutrients and organic materials to ocean waters • are important wildlife habitat
Types of Estuaries
Bolinas Lagoon Î
Types of Estuaries
• Salt Wedge – mouth of river flows directly into salt water – circulation controlled by river that pushes back the seawater – sharp boundary separates an upper less salty layer from an intruding wedge- shaped salty bottom layer – mouths of Mississippi, Columbia and Hudson rivers
Types of Estuaries
• Partially Mixed – tidal flow provides a means of erasing salt wedge – salt water is mixed upward and fresh water is mixed downward – Deeper estuaries such as Puget Sound and San Francisco Bay
Types of Estuaries
• Fjord-Type – characterized by a deep elongated basin that is U- shaped and a ledge or barrier that separates the basin from the sea – moderately high river input and little tidal mixing – found along glaciated coasts such as British Columbia, Alaska, Chile, New Zealand, and the Scandinavian countries.
Types of Estuaries
• Well Mixed – strong tidal mixing and low river flow that mix the sea water throughout the shallow estuary – mixing is so complete that the salinity is the same top to bottom and decreases from the ocean to the river – Shallow estuaries such as the Delaware Bay are well- mixed estuaries (Bolinas Lagoon)
Sometimes I think of the Bolinas Lagoon as a bathtub that empties and refills twice a day. It is definitely a shallow estuary that is well-mixed.
Equinox full moon tides Í
Solstice full moon tides Í
One of biggest factors operating on the lagoon is the tides. And they’re something to consider when you’re planning your day at the preserve. If you like to stop and Clem Miller Lookout and watch birds, you’ll want to take time of day (for sun glare) and time of tide into account.
Remember that we live in an area that has two high tides and two low tides per day. They are not the same height and they change depending on the earth’s position with respect to the sun and the moon’s position with respect to the earth. The highest and lowest tides are going to be around the full moon. Closer to the equinoxes the difference between the high-high tides and the low-high tides are less (and the low-low tides and the high-low tides).
I Iove this passage from “The Highest Tide” by Jim Lynch: Most people realize the sea covers two thirds of the planet, but few take the time to understand even a gallon of it. Watch what happens when you try to explain something as basic as the tides, that the suction of the moon and the sun creates a bulge across the ocean that turns into a slow and sneaky yet massive wave that covers our salty beaches twice a day. People look at you as if you’re making it up as you go. Plus tides aren’t news. They don’t crash like floods or exit like rivers. They operate beyond the fringe of attention spans…”
When is the best time to go tidepooling … a full moon around December 21st or a full moon around September 21st?
Another factor impacting what’s happening in the lagoon is the amount of rainfall which impacts the runoff/sediment coming from the watershed. During the months of June-September there is usually very little rain. That will impact the amount of freshwater entering the lagoon and the amount of sediment washed in.
What would you guess about the salinity of the lagoon in January compared to the salinity of the lagoon in September?
What other processes affect the BL estuary?
This diagram is from the Bolinas Lagoon Ecosystem Restoration Feasibility Study: Project Reformulation Final Report July 2006
As you can see there are a number of factors that effect the evolution of the lagoon that is an estuary. One result from the study that was fairly surprising is that the bulk of the sediment entering the lagoon is of marine in origin.
All of the documents that have been produced regarding the Bolinas Lagoon Study are available at www.marinopenspace.org. You will see a section called “Bolinas Lagoon Ecosystem Restoration Project” If you want to peruse the meat of the latest study go to the section reference above and look at Section II.
Estuarine Habitats
• Flood Tide Island / Shoal • Subtidal Channel / Shallow • Frequently Submerged Mudflat • Frequently exposed Mudflat • Eelgrass Beds (none in BL today) • Intertidal Salt Marsh • Brackish Marsh • Fluvial Delta (Pine Gulch Creek Delta)
Morphologic Units Year 2000
This diagram is also from the Bolinas Lagoon Study. One of the things the study looked at was how habitats would shift over time given the current sedimentation rates (and no earthquakes, a marginal estimation of sea level rise, and no human intervention).
The study found that salt marsh habitat and mudflat habitat would increase. Subtidal shallows would decrease. Pine Gulch Creek Delta would grow. The study also found that in the history of the lagoon (using sediment analysis) there is no record that the mouth has ever closed and it is unlikely that it will in the next 50 years. Zonation
When we were out there on the marsh, looking at these habitats, we noticed a distinct pattern of zonation. Mudflats cede to cord grass to pickleweed and salt grass and up to gum plant.
This diagram can be found in Chapter 7, Coastal Salt Marsh Vegetation, in the book Seashore Plants of California by Dawson & Foster. You can find a copied version of this chapter on the training website in the Lagoon and Salt Marsh Section.
What factors impact an organism’s ability to live in an estuary
• Salinity • Turbidity • Light • Temperature •Oxygen • Stability of sediments
Estuarine organisms can experience wide ranges of salinity due to freshwater input; tidal changes; evaporation.
Turbidity (amount of sediment in water column) can affect the ability of filter feeders to feed. It can also affect the amount of light.
Temperature can fluctuate widely.
Oxygen becomes depleted in the sediments (remember that black smelly mud we found pretty close to the surface when we were out on the salt marsh)
Sediments are shifting and changing.
Coping with Fluctuating Salinity • Freshwater Species • Brackish Water Species • Euryhaline Species (tolerate wide range) • Stenohaline species (narrow range)
• Osmoregulators (salmon, eels, some crabs, etc.) • Osmoconformers (mud crabs, polychaete worms)
Would osmoregulators have a tendency to be more euryhaline or stenohaline? What about osmoconformers? Estuarine Niches • Plankton – Phytoplankton – Zooplankton •Nekton • Benthos – Infauna – Epifuana – Meiofauna (interstitial)
Lets talk a little bit about the areas in the water column we might find critters:
Plankton: at the mercy of the currents (phyto = plant; zoo = animal)
Nekton: can motor through the water column under their own power – like fish. (anadromous fish migrate from sea to spawn in freshwater) & catadromous fish migrate from freshwater to spawn in sea). Some fish – like killifishes (Fundulus parvipinnis) spend their entire lives in estuaries
Benthos: live on the bottom. Epifauna live on the surface (moon snails) ; infauna burrow in the sediments (ghost shrimp, phornid worms) ; meiofauna live between the grains (gastrotrichs).
Some of Bolinas Lagoon’s charismatic nekton …
Anadromous fish like Steelhead and Salmon migrate from sea to spawn in freshwater
Both Steelhead and Coho salmon have been found in the creeks the empty into Bolinas lagoon.
Catadromous fish like the pacific lamprey migrate from freshwater to spawn in sea
Pacific lamprey are listed as being found in and around Bolinas Lagoon in the Bolinas Lagoon study. Some phytoplankton (although dinoflagellates are not technically phytoplankton) found in Bolinas Lagoon …
Plankton
Clockwise starting in the upper left: • Coscinodiscus (diatom) • Chaetoceros (diatom) • Foraminiferan • Two Dinoflagellates: One that looks like the Eiffel tower is Ceratium, other is Gonyaulux which is responsible for red tide. • Thalassiosira (diatom) • Radiolarian shell • Noctiluca (dinoflagellate responsible for bioluminescence)
What might be one of the advantages of having larval stages of your life cycle that have different niches from your adult stage?
Some zooplankton … who are they?
There are some fantastic critters floating around “at the mercy of the currents”. A good way to take a plankton tow without a boat is to drop plankton net in the mouth of the lagoon when the tide is coming in and just hang it out there for awhile. Hours of microscopic fun can follow!
Some zooplankton are holoplankton, meaning they spend their entire life in the plankton, like copepods. Others are meroplankton, which are only planktonic in their larval stages. The pictures of the zooplankton above are all meroplankton. Can you guess who they become?
These turn into
Starfish like our common ochre sea star (Pisaster ochraceous)
A veliger larva of a gastropod like the moon snail we find in our estuaries.
The larva of phoronid worm. The only part of this worm we usually see are the feeding appendages (lophophores) that stick up above the sediment. Some years you can see mini fields of these out at Limantour Estero. And I have found them in the lagoon and in Tomales Bay as well. (something that lives in the sediment is called what?)
One on the left is a napulius larva and the right is a cyprid larva. Both are larval stages of …
Barnacles! Here is our commonly seen acorn barnacle (Balanus glandula) Nemertean worm
Pilidium larva of an nemertean (ribbon) worm. Emplectonema gracile found in bolinas lagoon and tomales bay is the green worm on the left. These can stretch to quite some length.
Coastal Salt Marshes
• One of most productive habitats in the world • Salt water and freshwater mix • Nutrients & sunlight = miracle grow • Base of food chain is often detritus: particles are enriched by bacterial growth and other microorganisms • Provides habitat, food and shelter
The tidal salt marsh found in and around the Point Reyes Peninsula is limited to the periphery of estuaries consisting of approximately 1,000 acres. "They are distributed as follows: Bolinas Lagoon (240 acres); Limantour Estero (90 acres); Drake's Estero (160 acres); Tomales Bay (510 acres)" (Evens pg. 64, 1993). Although the salt marsh of the Peninsula is almost indistinguishable from that surrounding the San Francisco Bay, there are two species in particular that are absent from the Bay: Pacific Gumplant (Grindelia stricta) and Alaska Alkali Grass (Puccinelia nutkaensis) (Evens 1993).
Even though the Peninsula's salt marshes are very similar, there are variations among them that are worth noting. For example, Limantour and Drake's marshes receive less runoff than their inland counter parts, and, therefore, are more saline. They tend to be inundated by pickleweed (Salicornia sp.) and saltgrass (Distichlis spicata) . "The upper, less saline regions of these marshes are bordered by two members of the thrift family: sea pink (Armeria maritima) and sea lavender (Limonium californicum) (Evens pg. 65, 1993). In addition, north coast bird's-beak (Cordylanthus maritimus palustris) is a rare salt marsh species that can be found in association with sea lavender (Limonium californicum) along the protected edges of these westerly marshes (Evens 1993; Kozloff 1983).
What about salt marsh plants?
• Halophytes • Partially inundated • Some algae • Flowering plants adapted to salty soil • Zonation depends on – Tolerance for inundation –Amount of salt – Ability to compete with other plants
Saltwater habitats: Fringe Open (deep) water (bays, estuaries). Shallow water: plants can root in bottom and reach surface = salt marsh, brackish marsh. Salinity of salt marsh soil is 6 %.
Gas Exchange. Gasses penetrate water poorly. Deeper = airless. Obtaining vital gasses is a problem. Solved by hollow passages (aerenchyma tissue) from leaves to roots (Take a look at our freshwater cattails sometime). It’s possible to see oxidation of surrounding mud or the brown zone surrounding roots in otherwise black mud.
Halphytic plants are able to deal with salt… Salt poisoning. Plants must be able to adapt to changing salinity. Some salt marsh plants reverse the osmotic flow by concentrating salt in root cells. There are a couple methods of salt excretion: by glands on leaf surface (cord grass, marsh rosemary, salt grass); by deciduous joints (pickleweed).
Zonation. Depth of water and salinity of soil strongly influence the micro- distribution of plants. Plants in salt marsh can grow in fresh water habitats … they can just out-compete other plants in the harsher environment.
Zonation
Will often see bright green mats on exposed mud flats. Two fairly common types of green algae grow here. Ulva (sea lettuce) and Enteromorpha
Spartina sp. (cord grass)
• Low marsh plant • Epidermal salt glands • Arenchyma tissue
• Introduced invasive Spartina spp. out-competing natives
This is what we saw on our field trip…
The Spartina foliosa is dry and brown. You can still see that it is a uniform brown and the spacing
This photo Spartina foliosa at Walker Creek was taken at a time of the year when the native cord grass was greener (in the middle of the photo. You can still see the uniform color and the spacing.)
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ACR participates in Removing S. densiflora at Tom’s Point a larger project to survey Bolinas Lagoon and Tomales Bay for non- native species of cord grass. Here is a picture I took of some colleagues removing a clump of non-native cord grass from ACR’s Tom’s Point property.
Salicornia virginica (Pickleweed) Í Notice tiny flowers
Succulent, jointed stems
Another common name is glasswort (formerly used in glassmaking)
Used as a pickled vegetable in Europe Stores water in stems and salt in tissue (stores water to dilute excessively salty sap).
Turns red and tissue with excess salt falls of plant
Pickleweed replaces cordgrass right where soil salt content is highest. More tolerant of high soil salinity. Can see salt pans where even pickleweed can’t grow. (These salt pans are a good place for horn snails.)
Plants you will commonly find in and among the pickleweed in Bolinas Lagoon Salt Marshes:
Frequently grows mid- Jaumea carnosa marsh with Salicornia. Flowers most common May through October (found on entire coast)
Flowers about 1.5 cm across and Frankenia grandifolia pink. Alkalai Heath Inhabits upper marsh region
Distichlis spicata (Salt Grass)
Perennial. Can often find salt grass in dense stands
Grows in upper margins of marshes (above normal high tide line)
Excretes excess salt. Look at the leaves closely, you will often find salt grains clinging to them
Most common halophytic grass along sandy flats and salt marshes in California.
You can tell the edge of the marsh by where you see this large yellow composite. It won’t grow where it is inundated.
Grindelia stricta (Gum Plant)
(Picture taken a couple of days before our field trip)
Here it is in bloom (photo by May Chen)
Issues
• Human-induced sedimentation rates • Development / filling / dredging • Septic / run-off / non-point source pollution • Poor watershed management • Introduced species • Channelization • Oil spills
Bolinas Lagoon Project
• http://www.marinopenspace.org/ – Bolinas Lagoon Ecosystem Restoration Project • Bolinas Lagoon Ecosystem Restoration Feasibility Study: Project Reformulation Final Report July 2006