Nonetheless, as we were teaching third grade students about Food Webs in the Ocean last week and went to the dock at Trident Basin for a sample of life plankton, we noticed that from one week to the next the water suddenly teemed with thousands of the tiny larvae of barnacles. As we filled the jars with seawater, there was a slightly greenish tint to it indicating the presence of phytoplankton, drifting microscopic plantlike organisms. Microscopic life emerges in many shapes and layouts. For example, there are diatoms living in intricate glassy shells, often forming chains like tiny beaded necklaces and dinoflagellates, which swim around with a tiny hairlike flagellum that propels them through the water like a solar-powered mini outboard engine. These photosynthesizers supply the food for those thousands of little barnacle larvae and millions of other animal plankton from ultra-tiny to very small in size.
The sudden arrival of microscopic life in the water column is driven by the arrival of longer hours of daylight and the slowly rising water temperature and referred to as the spring bloom. Phytoplankton and the accompanying community of zooplankton feeding on diatoms or dinoflagellates or smaller zooplankton, one-celled animals and bacteria, are the basis for all production in the ocean. As diatoms and dinoflagellates take the energy from the sun and the nutrients out of the water, they grow rapidly by cell division. As this food source becomes available predictably with the lengthening of the days in spring, many animals time the release of their larvae to coincide with the presence of food.
If the strategy works, many larvae live to grow up. Moreover, if food is abundant they grow up quickly. In the eat-and-get-eaten world of the ocean bigger is better. The faster you grow the smaller is the number of predators that can eat you. Also, the bigger you are, the more things appear on your menu of potential prey. Here is how that works: A small fish with a small mouth can only eat small barnacle or copepod larvae. If it eats lots of them and gets bigger it may graduate to eat bigger copepods, then krill or shrimp, then other smaller fishes and finally larger prey.
Some animals don’t follow this strategy. The biggest of animals to roam this planet are not interested in eating big things at all. Baleen whales including Blue, Fin, Humpback, Gray and many more species sieve small animals out of the water column or, in the case of gray whales, the soft mud at the bottom. For a long time it was thought (and taught) that these whales don’t feed during their extensive migrations from warmer regions where they spend the winter months to the colder waters of the North that are rich in those small organisms baleen whales feed on in the summer. Newer articles, however, find that the whales do more than just swim from one place to the other. In fact, they follow the spring bloom northward. Closer to the equator, where spring comes earlier, the plankton bloom starts earlier. Further northward, where spring is later, plankton production is at its peak later in the year. In polar regions, it is known that rather than a spring bloom there is a summer bloom and it is short and very intense and productive. Radio-tagged whales showed researchers that they coordinated their trip north carefully with the abundance of their favorite food; krill. Far from starving along the way just to join the feeding frenzy in the North, fin and blue whales slowed their journey when food was there and moved more quickly when it was not, only to arrive at just the right time for the annual summer bloom party in the North. Happy whale fest!