Observations of Flowering Plants and the Main Vernal Pools on the Mesa de Colorado, 2/26/01 to 3/16/01

Chronological Observations

Introduction to this page

Observations 2000 November 4 - 2001 February 23
2001 February 26
2001 March 1
2001 March 3
2001 March 5
2001 March 9
2001 March 11
2001 March 13
2001 March 16
Later Observations

2001 February 26 (Day 13): Vernal Pool Trail. The shrimp are saved! The Pool looks like the usual Pool again. It is now 10" deep, gaining nearly 7" after 2" of rain in Fallbrook. The Pool's remaining lifetime of over 50 days is definitely enough for the shrimp to reproduce. The two smaller pools are brimming full, nearly connected by a ridge of standing water near the road.

I again was fortunate to get this hike in, with rain before my hike and rain after my hike. The weather was cool, with dark clouds around and a small breeze. This may have accounted for the very low density observed for the fairy shrimp today. I couldn't find any at all for about five minutes, then finally saw a few little ones, followed by a big one. But where do the shrimp go on days like this? Ranger Kevin Smith, who arrived just after I did, speculated that when there is a breeze, with the resulting surface water flow, they congregate on a side of the lake away from the boardwalk.

The largest fairy shrimp are now a whopping 1/4" long, much bigger than the 1/12" length from three days ago. It is very easy to see that they are swimming upside-down, legs up and attached to their 1/8" long body, followed by a tail of 1/8". The maximum density I observed was only 1 per square foot.

The new type of "gray shrimp" are definitely not going to evolve into "red shrimp", since the red shrimp are now present. The red shrimp are ~1/32" long, with a density of 100-200 per square foot. One can just barely detect that they are red. (See the next day's observation - it turns out these were not red shrimp.)

The two types of "gray shrimp" are much as they were three days ago. The rear-propelled gray shrimp are 1/32 - 1/16" long with a density of ~600 per square foot. The front-propelled gray shrimp are ~1/12" long with a density of ~1 per square foot.

The "black fleas" are still numerous, sometimes forming mats floating in the water, and the springtails number ~400 per square foot.

Observing the pond's creatures was difficult today. The lack of direct sunshine, and the reflected clouds, made it hard to distinguish the creatures from the water. The three-times deeper water column reduced the contrast further. In addition, the creatures weren't nearly as concentrated as before, being spread over a three-times deeper and somewhat wider pool.

Sometime in the last three days, Kevin placed two nice-looking signs at the Pool, warning people against going into or disturbing the Pool. Previously, there were no prominent signs warning people that this was a protected place, and hence many people did not know they were not supposed to disturb the pool's inhabitants.

I observed ~6 groups of toad eggs, including 3 strands that were newly laid. Most of the ones I had previous seen are probably dispersed among the vegetation within the Pool.

2001 March 1 (Day 16): Vernal Pool Trail, Granite Loop Trail. WOW! The Main Pool is Full!

Even the first glimpse from near the Display Board shows how different the Pool looks now. Water fills most of the view, with hardly a plant or rock poking out of the surface. The boardwalk looks nearly submerged, which it is, with the water level only inches from its surface in places.

The Pool is now as high as it ever gets, except briefly during heavy rain. Water is undoubtedly flowing through the outlet of the Pool as quickly as it is trickling in.

Conditions for viewing the shrimp are much better today. The sun is out most of the time, allowing plenty of contrast to see the shrimp. The maximum density of fairy shrimp is back up to 30 per square foot, and one can see them nearly everywhere. They have really grown, with many as large as 5/16 - 3/8".

The rear-propelled gray shrimp are still ~1/16" long, with a maximum density of 700 per square foot. The rotifers are also still ~1/16" long, with a maximum density up to ~5 per square foot. Springtails number ~200 per square foot at most.

There is an even higher density of very small (~1/32") creatures in the Pool, but they are too small to reliably identify them. Since no red shrimp are visible today, I conclude that the poor viewing conditions last time led me to erroneously identify them three days ago.

The deeper water and its movement have dispersed some of the toad eggs in the "honeymoon hotel" spot where they were first laid. Only three clusters are visible at that location, but Kay (another docent at the Pool today) and I spotted nine clusters in other locations. I caught a brief glimpse of a western toad diving under the boardwalk as I approached!

The first blennosperma (similar to goldfields) is blooming next to the Pool! A promise of what is to come.

2001 March 3 (Day 18): Vernal Pool Trail. Some of the fairy shrimp have egg cases! And for the first time, I saw Western Toads in the Pool for more than a quick glimpse.

I spent three hours at the Pool today as a volunteer Docent, helping ~60-80 people see the various creatures, answering questions about the Pool, and learning several things from some visitors. It was an enjoyable afternoon.

An article about the Pool had appeared in the Temecula newspaper this morning, which perhaps accounted for the large number of people. There was never a time during the entire three hours that there was no one else at the boardwalk with me.

Although the visitors kept me too busy to spend much time studying the Pool, the three hours spent at the Pool gave me a chance to see relatively rare events, like the Toads and perhaps even the observation of fairy shrimp with eggs.

As I was headed to the Pool, one lady told me that there were "three frogs in the water trying to kill each other"! My immediate guess was that two males were trying to mate with a female who ended up between the two males. Apparently, a male toad will try to mate with anything that moves, including another male toad. However, male toads have a special release call to alert any male who tries to mate with them that Hey, I'm a male, you dodo!. Hence the only configuration possible would be a female in the middle.

Unfortunately, people trying to touch the toads interrupted their breeding, and they were gone when I got to the Pool. However, it wasn't long before two individual toads were sighted: one underwater and one coming up for a breath. It takes very sharp eyes to pick them out on the bottom of the Pool, where they blend in perfectly with the vegetation. Although I only identified this toad later, its identification is easy - its length of 2-5" and the stripe down its back.

I observed no mating behavior while I was there.

After I got home, I found that these toads were not responsible for the eggs already in the water, since the western toad lays long strings of up to 16,500 eggs at one time! The eggs in the Pool since Day 1 come from the other species of toad known to breed in the Pool, the nocturnal 2" long western spadefoot toad. It breeds within days of the Pool filling.

The visibility of the fairy shrimp varied tremendously during the three hours. There were times when few shrimp could be seen, when clouds obscured the sun and the wind caused waves on the Pool's surface resulting in a significant circulation of the Pool's water. At one of those times, I saw a fairy shrimp bang directly into the boardwalk and turn around quickly. Perhaps when there is a current in the water, the shrimp tend to swim upstream to prevent being washed out of the Pool into the overflow channel. If so, that would account for the lack of shrimp at the boardwalk, since I have observed that the current is almost always toward the boardwalk, which would place the shrimp farther out into the Pool. Also, without direct sunlight, the contrast of the shrimp in the water is much reduced.

When the Pool was calm, and it was sunny, the shrimp were easily visible. However, a fair amount of scum obscured the water next to the boardwalk in many places, cutting down the number of possible viewing locations.

The maximum density of fairy shrimp was ~5 per square foot, and their maximum size was about 1/2". None of the fairy shrimp had any eggs cases visible, until two hours after I arrived, when suddenly nearly every shrimp I saw had egg cases! This of course made it difficult to properly estimate the percentage with egg cases. Estimating solely from the total number of fairy shrimp I saw today, perhaps about 5% of them had egg cases.

The rear-propelled gray shrimp were still ~1/16" long, with a maximum density of ~600 per square foot, and the gray rotifers were perhaps 3/32" long with a maximum density of ~5 per square foot. The wriggly red worms had a maximum density of ~2 per square foot. I failed to estimate the density of springtails, due to the press of the visitors. No red shrimp were visible.

One visitor reported that milkmaids and redmaids were blooming now, but I didn't journey past the Pool today to see for myself. I had a fascinating conversation with a biologist, who answered several of my questions. In particular, it has always seems surprising to me that so many insects specialize to eat only one species of plants. She said that a popular theory to explain that behavior was that since plants are always evolving their toxins to stay one step ahead of insects, that it conserved energy for an individual insect species to concentrate on detoxifying the compounds of one specific plant species. Makes sense to me!

2001 March 5 (Day 20): Vernal Pool Trail. It was not a good day to observe the Pool, since it was very windy. There were large ripples on the surface of the Pool, and putting one's face just above the water for any extended time led quickly to seasickness.

There were two main changes today, one by land and one by 'sea'. By land, dragonflies were everywhere! They escorted me to the Pool, distracting me with their amazing flying abilities. At the Pool, they showed off their ability to perform acrobatics while mating! I wonder what dragonfly nymphs look like...

In the Pool, after much study and observation, I finally saw the Pacific tree frog's eggs. (Compare the previous photo with this one to distinguish the yellowish eggs at the bottom of the Pool from other things floating in the water.) Unlike stringy toad's eggs, frog eggs are more roundish, and are not connected together. Now I am waiting only to see the strings of up to 16,500 eggs from the Western Toad!

I walked the entire perimeter of the boardwalk four times to see Western Toads or their strings of eggs, to no avail. One creature jumped into the Pool from the boardwalk as I approached; it likely was a Pacific tree frog.

The choppy pool made it difficult to make good measurements. The fairy shrimp might have been a bit larger than the 0.5" of two days ago, but I couldn't measure this with any certainty. Most of the fairy shrimp were about 1/4" long. Their numbers were definitely up, a maximum of 50 per square foot today. In addition, I'm fairly sure that I saw densities of about 200 per square foot of 1/16" fairy shrimp that probably hatched when the Pool expanded significantly from 2/26 to 3/1. Time will tell.

The rear-propelled gray shrimp were still ~1/16" long, and numbered ~200 per square foot at peak. The rotifers were ~3/32" long, numbering ~3 per square foot at peak. There was an amazing collection of ~40 wriggling red worms per square foot just north of the center of the boardwalk. I saw 10-15 clumps of western spadefoot toad egg clumps.

On the surface, there were only ~10 springtails per square foot.

Away from the Pool, more blennosperma are beginning to bloom, with one or two popping up in many places. Milkmaids are absolutely lovely along the Los Santos Trail, and the first blue dicks are blooming.

2001 March 9 (Day 24): Vernal Pool Trail. It was an even worse day to observe the Pool today, since not only was it was very windy, it was also quite cold and cloudy, with rain in many spots near to the Plateau.

There was no hope of observing any frog or toad eggs, since the water was even choppier than four days ago. Fortunately, observations could still be made in a sheltered corner of the boardwalk for the smaller creatures, and the shrimp are so large that they can be picked out in many other places.

The fairy shrimp range in size from 1/4" to some giants at 3/4". A large percentage of the 1/2" and longer shrimp have eggs, perhaps about 20%, although the exact percentage was hard to estimate. Some have just a small roundish egg case, whereas others now have longer egg cases. I saw one shrimp that appeared to be fighting with itself, zooming and darting around, twisting and turning itself into contortions. The source of this weird behavior became apparent when a piece of algae nearly as large as the shrimp finally disengaged, and the shrimp went merrily on its way.

The other creatures were much the same as normal. Springtails and the rear-propelled gray shrimp each numbered up to 100 per square foot. The rotifers were still ~3/32" long and numbered about 1 per square foot. I saw several 1/4" long flatworms on the surface. Some of the smaller creatures have grown larger, and I now think that they are baby tadpoles about 3/32" long! (They turned out to be "red shrimp": see below.) They have what appears to be small tails, and their roundish front parts are a bit reddish.

2001 March 11 (Day 26): Vernal Pool Trail. Keeping the string of bad weather days intact, it again was a cold, cloudy, sprinkly day at the Pool. Nonetheless, about 40 or so hardy souls came to the Pool during the 2.5 hours I docented there today.

Again, it was hard to get good numbers for the Pool's creatures, due to the weather and the press of visitors. But the addition of so many eyes, and the long time spent at the Pool, more than made up for those hindrances.

Amazingly, about 75% of the larger fairy shrimp (1/2 - 3/4") have egg sacs! This is far far greater than I have ever observed before. The highest percentage observed in prior years was only 10%! This high number implies that females make up much more than 50% of the shrimp population, which is known to happen at times. It also means that the Riverside fairy shrimp, which grow to 1" long, are a small component of the total population. Eggs were observed on some shrimp as small as 3/8" in length.

The large size of the majority of the fairy shrimp and their white egg sacs make them quite visible. Nonetheless, nearly everyone I met coming away from the Pool told me that they had not seen the shrimp. In giving tours of the pond to over a hundred people now, it has become clear to me that probably the majority of the people cannot see the shrimp until someone tells them what to look for and points them out repeatedly until the shrimp are sighted. Once people know what to look for, nearly everyone can immediately see dozens more of the shrimp within seconds. Today some people spotted clusters of shrimp easily from a standing-up position, after they learned what to look for!

The reddish creatures that I thought could be baby tadpoles now turn out to be the familiar 'red shrimp', probably a copepod of some sort. They now have two antennae clearly visible at their head, and a clear antennae at the rear, not a 'tail'. My apologies for calling them 'tadpoles' to everyone today without the "possible" qualification; I only observed the antennae clearly at the end of the day, when I could study them for some time uninterrupted. (We scientists always take oral statements with a huge grain of salt, since even the most eminent scientists forget to give the qualifiers and disclaimers orally, or say things they didn't intend to say and don't catch the errors. We spend hours and days when writing papers to put in such weasel words and to get our statements correct! Oral communication just doesn't allow the luxury of getting it completely correct. (;-) )

With the appearance of the red shrimp, all the familiar pond creatures are present except for the tadpoles, which will surely come soon. Surprisingly, the pond resident observed only this year by me, the rear-propelled gray shrimp, were nearly absent today, at a density of only ~1 per square foot.

The old clusters of western spadefoot toad eggs are almost all gone, but new clusters continue to be laid. There was still no sign of the western toad eggs.

The fairy shrimp ranged in size from 1/4 - 3/4", with a density of up to 8 per square foot. The red shrimp were 1/16 - 3/32" in length, up to 3 per square foot. The rotifers were 3/32" in length, up to 3 per square foot. Springtails and flatworms numbers up to 10 per square foot.

One visitor pointed out a single fairy shrimp that stood out from all the rest - it was not transparent! It had a vivid clear color, one I did not note since I was so shocked at the time by its appearance. The color may have been a whitish-red, almost reminiscent of the shrimp we eat.

Again, spending several hours at the Pool aided by the eyes of many visitors is a good thing!

2001 March 13 (Day 28): Vernal Pool Trail. It was a beautiful day, sunny and pleasant, sans wind, with one exception: vast clouds of mosquitoes! Within moments of getting out of my car at 2 pm, my beige shorts were covered with perhaps 20-30 mosquitoes. Fortunately, they were male mosquitoes, and didn't bite. Whew! (Reserve Naturalist Rob Hicks identified them as male mosquitoes from their antennae.)

When I got to the Main Pool, the surface was absolutely calm until I started taking measurements! Then the wind came up, producing the usual choppy surface. Sigh....

The fairy shrimp ranged from 1/4 - 3/4" in length, with a maximum density of ~10 per square foot. About half of the 3/8" length fairy shrimp showed egg cases, as did an amazing 90% of the 1/2" length shrimp! The egg cases came in two forms: a thin linear white case and the same case with a white bulge at the top. I suppose the ones with a white bulge are the ones with eggs developing in them.

I need to learn more about the reproductive habits of the shrimp. One source says that male fairy shrimp die within a few hours of copulation, which certainly could account for the large number of females observed with eggs!

Three western toads were spotted in separate areas near the boardwalk. Only three sets of western spadefoot toad eggs were visible, continuing the decline from a peak of ~12 on day 15.

The other creatures were much as before. Maximum densities per square foot: springtails, 1; gray shrimp, 3; red shrimp, 3; rear-propelled gray shrimp, 3, red worms, 2. I only saw one dragonfly.

The first gold carpet (from blennosperma) is beginning to show just on the other side of the Pool.

Multiuse Trail. A number of plants are beginning to bloom along this trail (see bloom observations). About 1% of the hoaryleaf ceanothus have blooms, and the rest have very fat buds. They will look and smell spectacular soon. The mission manzanita, on the other hand, is showing an anemic full bloom, much less showy than last year.

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Copyright © 2000-2003 by Tom Chester.
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Updated 28 January 2003.