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TEACHER

PAGE

Lesson Three – The Three Phases of the Vernal Pool Ecosystem

Objective: Students learn the three phases of vernal pools and the connection to the water cycle.

Time: 45 minutes

Key words: bacteria, protozoa, detritus, algae, aquatic, spores, cysts, invertebrate, food web,ecosystem, endemic, adapt, adaptation

Advance Preparation:• Make copies of the Student Pages titled “The Wet Phase: Winter in the Vernal Pools,” “The

Flower Phase: Spring in the Vernal Pools,” and “The Dry Phase: Summer and Fall in theVernal Pools.”

• Make copies of the Worksheets titled “Three Phases of a Vernal Pool,” “Vernal Pool Cross-Section Worksheet” and “Vernal Pool Phases Worksheet.”

Procedure:1. Review vernal pool knowledge. Play the video again, if necessary.2. Pass out and read the three Student Pages. Add to portfolio.3. Pass out the “Three Phases of a Vernal Pool Worksheet.” Have students color the Worksheet

and write in the phases and seasons.4. Pass out “Vernal Pool Cross-Section Worksheet.”

• Use the overhead of the “Vernal Pool Cross-Section Worksheet” to discuss the impor-tance of water levels in a vernal pool grassland. (Teacher talking points are provided onthe Answer Sheet.)

• Ask these questions:- Where is the water table during the wet phase?- Where are the possible levels of the water table in the spring?- What happens to the water table during the dry season?

• Have students illustrate on the Worksheet what happens to the water level in vernal poolsduring each phase. Optional: Students can label the following on their cross-section: soil,hardpan, mima mound, vernal pool, water table.

5. Pass out and have students complete the “Vernal Pool Phases Worksheet.”

Evaluation/Extensions:• Students complete 3 Worksheets and add to portfolio.

Discussion Topic:• If you were a burrowing mammal (Pocket Gopher, California Vole, Black-tailed Jackrabbit,

or Coyote) where could you make an underground burrow in the winter and not get wet?Would you tunnel straight down or at an angle? Why?

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The Three Phases of the Vernal Pool Ecosystem

The Wet Phase: Winter in the Vernal Pools

As soon as the winter rains begin to puddle in the vernal pools, tiny creatures called bacteria andprotozoa spring to life. Many of them feed on detritus, bits of dead plants and animals that lie onthe bottom of the pool. These detritus feeders are, in turn, eaten by many other tiny animals. Micro-scopic (very tiny) green plants called algae are the next to appear. They are like tiny floating foodfactories, providing the energy that powers most of the other species in a vernal pool.

Now that the winter pools are full of water and are teeming with bacteria, algae and protozoa, manymore aquatic species begin to appear. The water signals to the resting spores, eggs, and cysts ofaquatic life that it is time to hatch and grow. Within a few weeks, dozens of species of inverte-brates (small animals without backbones) will be living in the pools. Each aquatic species musthurry and complete its life cycle before the pool dries out in the spring.

When vernal pools are full of aquatic life, it’s like putting a meal on the table. Frogs, snakes, birds,and mammals come to the vernal pools for dinner. The food web connects all the species in thevernal pool grassland ecosystem. An ecosystem is a community of plants and animals that dependon one another and their environment for survival.

This baby Water Flea is surrounded by microscopicdiatoms. Protozoa, bacteria, diatoms, and algae are allmicroscopic, meaning we need a microscope to see themat all.

An aquatic beetle larva known as a “Water Tiger” eats aWater Boatman. Like many invertebrates, they aremacroscopic. Although you can see them with your nakedeye, you need a magnifying lens to see their parts.

Pacific Chorus Frog

Fact of Life: Not every individual of a species will survive longenough to reproduce. Most will become food for another creature. In anecosystem the survival of the individual does not matter. The survivalof the species is what is important. As long as some individuals repro-duce, the species will continue.

We know very little about this ecosystem and the species that call ithome. There is so much left to discover. However, we do know onething for sure: vernal pool creatures need clean water. Clean water isthe key to abundant life.

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The Three Phases of the Vernal Pool Ecosystem

The Flower Phase: Spring in the Vernal Pools

Spring is a beautiful time to visit a vernal pool grassland. As the pools dry down in March, the seedsof vernal pool plants grow in the muddy soil. Over 200 plant species can grow in vernal pools.However, over 60 of these species are endemic to vernal pools, meaning they can grow only invernal pools and nowhere else. If not for vernal pools, they would become extinct.

The plants grow quickly alongthe shrinking edge of thewater. Within four weeks theycover the entire bottom ofeach vernal pool. As the firstplants bloom, their flowerscan make colorful ringsaround the outside of thepools. During the month ofApril, the display of wildflow-ers in the pools changes fromweek to week. By late April,yellow, white, pink, andpurple flowers carpet thepools with splashes of color.

Vernal pools are like snowflakes in that no two are exactly alike. While each pool usually has 15 to20 different species of wildflowers in it, the mix of species can be different in every pool. Plantsselect their host pools based on the growing conditions of each vernal pool. Some plants prefershallow pools that dry quickly or the higher, drier areas within deeper pools. Other plants growwhere the water is deeper and lasts longer into the spring. Most of the habits of vernal pool plantsare still a mystery to scientists.

These pink monkeyflowers grow well on bare mounds ofsoil heaped up by pocket gophers that tunnel under thevernal pools searching for Brodiaea bulbs.

These plants bloom late in spring. The bulbs of theBrodiaea (larger flower) are a favorite food of Botta’sPocket Gophers. Few vernal pools host Douglas’sBeardstyle; it needs very special conditions to grow.

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The Three Phases of the Vernal Pool Ecosystem

The Dry Phase: Summer and Fall in the Vernal Pools

By the beginning of summer, the soil in thebottom of the vernal pools cracks and dries.Temperatures in the Central Valley reach over100 degrees Fahrenheit. Most of the vernal poolplants dry up and turn brown. All the aquaticlife dies or leaves the pools.

Although the critters are gone, they leave behindthe eggs, cysts, spores and seeds that will carrythe genes of their species through the long, hotsummer. Each species has a way to survive thenext eight months of drought. It has takenmillions of years for them to adapt to live inthis ecosystem. We have yet to discover thespecial adaptations that allow most vernal poolspecies to survive in this harsh environment.

Scientists have found Fairy Shrimp eggs (called cysts)over 100 years old. When the cysts were put in water, theyhatched. This cyst is seen with a special microscope thatmakes it look 100 times larger than normal. The FairyShrimp in the photo is 5 times larger than normal size.

Although it can look dry and barren, the grasslands and vernal pools support many species throughthe summer and fall. The seeds left by spring plants provide food for insects, birds, and rodents.Pocket gophers travel underground through a shallow system of burrows. They search for plantroots and bulbs, while hiding from the watchful eyes of hungry hawks and coyotes. Toads and frogsseek shelter from predators and the drying sun in these rodent burrows. Snakes slither through thedry grass poking their heads into the burrows, looking for dinner. The food web connects manyspecies, even when this wetland isn’t wet.

In the dryness of fall, it is hard to imagine that in a few weeks the winter rains will return. Thesebone-dry pools will fill up with runoff and the life cycle of hundreds of species will begin again.Vernal pools will add another year to their long history, giving us another year to investigate theirmany secrets.

Waiting for Rain

STUDENT

WORKSHEET

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Name:_______________________

Three Phases of a Vernal Pool

Write the names of each season and phase. Color.

__________Phase

__________Season

__________Season

________ & ________Seasons

__________Phase

__________Phase

STUDENT

WORKSHEET

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STUDENT

WORKSHEET

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Name:_______________________

Vernal Pool Phases Worksheet

Conditions change quickly in a vernal pool. To show your understanding of the three phases, writeW for wet phase, F for flower phase, and D for dry phase.

_____ The soil is cracked and dry.

_____ Algae (very small green plants) appear.

_____ Vernal pools fill with water.

_____ Animals visit the vernal pools looking for seeds.

_____ Aquatic life hatches and begins to grow.

_____ Flowers bloom and the vernal pools dry up.

_____ Animals visit the vernal pools to dine on small aquatic animals.

Draw a line to connect the two matching items:

algae bacteria & protozoa

animals without backbones macroscopic animals

ecosystem detritus

bits of dead plants and animals invertebrates

Pacific Chorus Frog tiny green plants

microscopic creatures an environment and its community ofplants and animals

Write T for True and F for False next to the following sentences:

______ Vernal pools are all the same.

______ Clean water supports abundant life.

______ The flowers found in vernal pools are found in many other places.

______ As long as some individuals of a species reproduce, the species will survive.

______ During the summer and fall, no animals are found at the dry vernal pools.

______ Scientists know everything there is to know about vernal pool plants and animals.