In fulfilling their own individual needs of reproduction, copepods play a vital role in service to the wider ecology of aquatic environments. As consumers of bacteria and phytoplankton, and as the food source organisms for small fish, whales, seabirds, and other crustaceans such as krill, copepods are integral to food chains. They most likely provide the largest biomass in the oceans, and indeed millions could be found in a cubic meter of sea water. As a result of their key role, they are also of indirect value to humans.
For such a small organism, ironically they became the center of a controversial debate in New York City in 2004. When Jewish rabbis in Brooklyn spotted small copepods in lettuce washed via public tap water, it lead to a controversy whether the tap water was kosher. The problem centered on the biblical prohibition against eating water-borne creatures that lack fins and scales. While this prohibition is limited to organism that can be seen with the unaided eye, some copepods reach two millimeters, large enough to be seen a specks in the water. Conflicting views arose as to whether the unfiltered water could be used to drink, cook, wash dishes, and brush teeth. As a result, many orthodox Jews installed water filters—although another debate was whether one could do filtering on the Sabbath.
One Jewish professor of history captured the issue in this manner: "The notion that God would have forbidden something no one could know about for thousands of years, thus causing wholesale, unavoidable violation of the Torah, offends our deepest instincts about the character of both the Law and its Author." Another individual, a Rabbi, concluded "The hidden things belong to god. We are responsible for what we see. If you know about it and don't see it, then it doesn't exist. So those who drank the water before were drinking kosher water." (From Berger, J. 2004. The water's fine, but is it kosher? The New York Times November 7, 2004. Retrieved November 25, 2007.)