57,160

That's the total number of nematodes I have counted from my sediment samples since October 2020 when I did my first sediment collection in St. Andrew Bay. I thought I would take the time to total up the numbers and I am shocked at how many i have counted. Every once in a while I have an outstanding sample with more than 1500 nematodes, and there are really odd cases where I have more than 2000, but I did not expect that the total number of nematodes across all of my research is more than 50,000. This number is important because it highlights the need for an important step in my research: subsampling. This week I will briefly talk about the subsampling process, including what it is, why we do it, and our confidence in the processes, as well as provide quick updates at the end.

Subsampling, as the name implies, is the process of taking a smaller sample from an initial set of conditions. In my research, subsampling means that I use a fraction of the total sample to draw conclusions about the rest of the sample. In our lab, as well as many other meiofauna and nematode labs, we choose to analyze the first 100 nematodes in a sample and assume that the 100 nematodes are representative of the whole. How do we select the first 100 in an unbiased way? I have shown counting dishes in previous blog posts, but we pour the sample into a gridded petri dish and move through each of the grid squares from left to right, picking out any nematodes we encounter. Once we have extracted the first 100, we continue counting the rest to understand what percentage of the total sample we have extracted. In most of my samples, 100 nematodes represents more than 10% of the total nematode count, which is pretty good. Obviously the more nematodes we extract, or the higher the extraction percentage is, the more representative the subsample is of the larger sediment environment. The main reason that we use subsampling in our work is because of the time required to identify nematodes to different taxonomic levels (Genus or Species). While charismatic megafauna (like fishes, birds, etc.) often are easy to identify to the Genus level, nematode identifications require more finesse because of their size.

How confident are we in the results from subsampling? I think the answer depends on the research question that we are asking. For my research, I want to know what differences exist in nematode communities at sites of wastewater treatment outflow compared to sites where there is no direct pollution. While there may be rare individuals in both environments, there's still a high likelihood that I can identify differences in the communities by extracting 100 individuals. I think that if I was asking a really nuanced research question and using nematodes to identify subtle differences in environmental conditions, I might want to identify more individuals because the differences in diversity metrics (values we use to assess differences in community compositions) may be more narrow.

Next week I will start identifying nematodes under the microscope and I hope to get some good pictures of what these microscopic animals look like under high magnification so that you can see some of the subtle differences I have mentioned in past blogs. While I will continue to provide updates on this stage of my research, I may write about other side projects that I am undertaking (helping out other graduate students with research) to show you some of the other fascinating work that is happening in our department and at the marine lab. Stay tuned!