An anemone
I visited my selected tide pool once a week for six weeks to officially record air temperature, water temperature, and overall weather conditions. My observations included the overall percentage of marine life in a one-meter-by-one-meter square in my selected pool. To calculate this percentage, I observed the numbers of mussels, hermit crabs, sea urchins, barnacles, chitons, and, in particular, the number of anemones visible at each observation. In the observation site, most of the area on the bottom of the tide pool was occupied by some form of marine life. A few areas were empty, with rock visible but no marine animals. The "percent marine life" is a semi-quantitative estimate of the percentage of the total area of the one-meter-square observation site that was occupied by marine animals. The times of my visits varied considerably due to the timing of low tides. I also took a 1cc sample of water from the tidal pool, which I would analyze in the second part of my expedition.
Allison taking a sample
Gathering the samples and performing my counts was a tremendous amount of fun. Once, an older gentleman approached me while I was measuring the temperature of the water in my tide pool and commented that he thought my thermometer was "off" by up to 4°C! There was a great deal of interest in my project from both the locals and visiting tourists, all of whom seemed genuinely interested in the final results of my expedition.
Following the six wonderful weeks of the first part of my expedition, it was time for me to embark on the second part of the adventure—an analysis of my water samples in my father's research laboratory at the University of California - Irvine Medical Center. To prepare for this part of my project, I first made bacterial growth plates. I mixed tryptone, yeast extract, salt, and agar together and then autoclaved, or cooked, the mixture at 121°C for 30 minutes in order to make sure that it was sterile. After letting this media cool to 55°C, I poured the liquid into Petri dishes and let them solidify overnight. This was an important part of my expedition, because if the growth material was itself infected with bacteria, I would not be able to evaluate the amount of bacteria actually found in the ocean water.
|
 
Top: Allison at work in the lab; Bottom: Bacteria culture in a petri dish
Next, I nervously began my efforts to grow bacteria from the ocean water samples. I had collected the 1cc samples in little plastic tubes. I centrifuged these six tubes at 14,000 rpm for seven minutes. At first I wondered why it was necessary to separate out the bacteria from the ocean water in a centrifuge, but since I only need to use the bacteria, not the water itself, the centrifuge is an ideal method for separation so that I had easier access to the bacteria. In fact, I was able to throw away the seawater. I then placed the remaining pellet of bacteria in 50 microliters of LB bacterial growth broth and put it in a water bath at 37°C for 30 minutes in order to relax the bacteria and make it easier to work with. Finally, the fun began when I used sterile technique to spread bacteria from each sample over its own, individually labeled Petri plate. I placed each dish in a 37°C incubator to see if anything would grow overnight. Although I was not certain, I felt confident that if bacterial colonies did not grow in 24 hours, perhaps they would grow in 48 hours. Worrying continuously, I anxiously waited for 24 hours to pass. After all, the future of my whole expedition depended on the outcome of these six plates! Delighted and ecstatic, I discovered that large and small, beige and transparent bacterial colonies covered my plates after only 24 hours. I took pictures of all of the plates to document my results, and made an effort to describe the colonies and the environmental conditions that existed during the time that the sample was collected. Finally, it was time for a mental expedition—a trip that would cause me to think more deeply about life in the tide pools that I love so much.
Table 1: Field and Laboratory Data (Click to enlarge)
Several results caught my attention almost immediately. First of all, the number of beige bacterial colonies changed quite a lot. (See Table 1.) In my earliest samples, there were a great many of these colonies, while there were far fewer in the later samples. On one visit, on October 30, there were many transparent colonies. What had caused the difference in numbers and types of colonies became one of my first expedition mysteries. I also noticed that the temperature of the ocean water declined steadily over the six weeks. This was not unexpected, but I was pleased to note that at least one of my predictions had come true. However, the air temperature varied without any particular pattern, probably because the times of my visits to the tide pools depended on the tides and not on the time of day. The average air temperature for the week preceding my visits declined steadily over the six weeks of my expedition, which was also expected. Two of my expedition dates, October 24 and October 30, were preceded by very heavy rainstorms. The estimated percentage of marine life in the one-meter-square area fluctuated between 65% and 80%, without any clear pattern. Finally, the number of anemones remained constant—between six and eight. All of these results were very interesting, but what did they mean for my expedition?
|
