How to Count Invertebrates

By Karen Weinstock

At La Selva, we have been working on our independent projects. Laura and I decided to work together because we both agreed that we want to avoid circumstances that would expose us to snakes and bullet ants. Therefore, we decided to work with aquatic communities. Since the river is dangerous and incredibly difficult to work with, we chose phytotelmata aquatic communities. Phytotelmata are water communities enclosed by plants, such as pitcher plants or tree holes, and are very common in rainforests. We decided to talk to Carlos, the resident aquatic invertebrate expert, who was excited about the possibility of us working with heliconia plants that have phytotelmata. From there, Laura and I came up with a question. The question needed to be feasible to do in 5 days and have ecological significance, so we decided to see how invertebrate communities in heliconias respond to increased light due to edge effects. The question seemed simple enough, but along the way we realized we were very wrong.

            First, we needed a heliconia species that existed inside the forest and on the edge of the forest in high light. Unfortunately, heliconias are very particular about their habitats and there would not be a species that grows inside the forest and in open fields. Thus, Laura and I decided to talk to Orlando, the resident plant expert. He took us through the list of heliconia species present at La Selva, and introduced us to Heliconia imbricata, which grows inside the forest and on trail edges. Ok, we thought, we’ll change the question to inside the forest and on trail edges. In practice, however, it was not that easy. Many heliconias weren’t in bloom, and the ones we found were left over from last season, so they were few and far between. Besides, finding them deep in the forest off trail edges was trickier than we originally anticipated. In fact, we didn’t find any off trail at all. We changed the question once more: how do aquatic communities in heliconias change along a light gradient? That way, we could sample from all of the imbricatas that we foundand not worry about finding enough in two distinct conditions.

            With this figured out, we collected our samples and took them back to the lab. As we started counting the microinvertebrates, we came upon a problem of macro magnitude. In approximately 10 mL of water collected from a heliconia, we were looking at thousands of microscopic organisms swimming around, and as you increase the magnification, more and more micro-creatures appear. We realized counting these creatures would be impossible, so we decided to count from 1 mL. 1 mL was also too much to observe at once, so we counted microinvertebrates in 20 sets of 50 microliters, and only what we could see with a maximum of 4x zoom. We found 4 differently shaped creatures, which we didn’t know how to identify, so we nick-named them until we could ask Carlos for help with identification.

In the end, we were able to gather all of our data and put it together in a spreadsheet. More problems arose with statistical analysis, but we managed to figure those out as well. I learned from this 5 day research project that things never go as planned, and nothing is ever as simple as it seems. Creativity and problem solving are incredibly important in science, and not every roadblock signifies the end of the journey. Without creativity and persistence, we would have never found solutions to our unforeseeable problems. Although, next time, I will be sure to run a pilot for my project!