The vast majority of life in the ocean is really, really small. So small, that by scooping up a single cup of seawater you encounter a vast menagerie of planktonic creatures that far eclipses even the most prodigious zoo. Despite their generally modest size and limited mobility, plankton play an important role in the ocean and are some of the most captivating animals around.
As we cruised down Grappler Inlet near Bamfield we saw bald eagles, kingfishers and ducks, but the real biological boon was flowing all around us. Our goal was to compare the plankton communities from different depths and locations within the inlet (the mouth of Grappler is saltier than the interior). We measured conditions at the sites, and trawled a plankton net behind the boat to collect organisms. Plankton, by definition, cannot swim against the current so they are relatively easy to capture.
Some plankton need sunlight to produce food and are found in shallow or clear waters, while others hide in the dark depths to avoid predators. Some plankton prefer fresher water while others like it saltier. Some travel up and down in the water; this micro migration plays out daily as some animal zooplankton hide during the day and rise at night to feed on other zooplankton and plant-like phytoplankton . Because we sampled during the day we expected to find more of the larger zooplankton lurking in the deeper water.
Sampling the water yielded a cornucopia of planktonic species. We found predominantly copepods and a few phytoplankton at the surface while the deeper samples had higher numbers of crab larvae, shrimp, mussel larvae, and snail larvae, to name a few. Surprisingly, many large, charismatic ocean animals start their lives as humble plankton! As we predicted, there was a higher number of larger zooplankton in the deeper samples, and the saltier of the two deep samples held the tigers of the plankton world: arrow worms.
Perhaps humble is a misleading moniker for plankton, because they punch above their weight across the globe. The majority of the oxygen we breath, around 70%, is produced by organisms in the ocean. Plankton are also food for many larger creatures, meaning some of the largest animals on the planet are sustained by some of the tiniest. We may not be able to easily see them without a microscope, but we owe a tremendous debt to plankton for all they do for us and the planet. Plankton are tiny heroes, deserving tremendous appreciation for their contributions to the environment.
The Tara Expedition traveled the world’s oceans to study the incredible diversity of plankton, and is a great place to find more information: http://oceans.taraexpeditions.org/en/m/science/results/eukaryotic-plankton-diversity-in-the-sunlit-ocean/