This is one of the problems that we have in sampling organisms, particularly underwater organisms and if they're microscopic. We go out and we collect samples with nets. We bring them back to our lab and we analyze them under a microscope. It's very painstaking work. Typically, what a plankton ecologist would do is sample from that mixture and count and identify the first 300 or so organisms that you encounter in the sample.
The problem with that approach, and it's one that people have been using for hundreds of years, is that if organisms are present at abundances lower than one in 300, then the likelihood that you are going to pick them up in your microscope count is very low. In reality, there are probably many organisms that are found in nature that are found at one in a million or one in 10 million.
So there's an entire array of species that occur in aquatic ecosystems around the world that we rarely detect because their presence is so low. But if we use environmental DNA, you can track either the species itself or you can track the DNA that it's excreting into the water, and every species will leave a telltale signature.
So we're using a gene that is different for every single species, and instead of trying to identify the species the way we historically would do, we instead analyze the DNA and then we cross-reference the DNA to online databases. From that we can determine how many species there are.
In many cases, I can't give you the species' name, but I could tell you, in the example I just quoted from, that the two most common groups that you would find in an aquatic ecosystem are called copepods and cladocerans. Particularly for copepods, the taxonomy of that group is very difficult. It's hard to identify organisms. Consequently, frequently when people do an assessment of a plankton assemblage, say, from the port of Hamilton, they might count 15 species. When we do DNA work, instead we may get 60 species. So that's where the difference comes from.