Whales are the largest animals on Earth, and their immense size leads to curiosity about what sustains them in the vast ocean. These marine mammals, called cetaceans, have evolved specialized methods for finding and consuming food. Understanding their diet is complex, as their eating habits shape the entire ocean ecosystem and illuminate the intricate balance of the marine food web.
The Primary Producers
The question of whether whales consume phytoplankton is often asked because these microscopic organisms form the basis of all life in the ocean. Phytoplankton are tiny, single-celled organisms that perform photosynthesis, converting sunlight and carbon dioxide into energy, just like plants on land. They are the primary producers, fueling nearly every other organism in the water column.
Whales do not feed directly on phytoplankton due to the size difference. Instead, their main food source, zooplankton, consumes the phytoplankton. Zooplankton are small, often microscopic animals that drift in the water, grazing on the primary producers. This places the largest whales one step higher on the food chain, feeding on organisms that have already concentrated the sun’s energy.
The True Diet of Filter Feeders
The largest whales, such as Blue whales and Humpback whales, belong to the suborder Mysticeti, or baleen whales, which are filter feeders. The bulk of their diet consists of zooplankton, including tiny crustaceans like copepods and, most famously, krill. Krill are small, shrimp-like organisms that congregate in dense swarms.
The volume of food required to sustain these giants is staggering. A single Blue whale may consume around 16 metric tons of krill in a single foraging day. Baleen whales feed intensely for only 90 to 120 days a year in productive waters, storing energy as blubber to sustain them during migration and breeding.
Different species specialize in different prey. Right whales use fine baleen plates to filter smaller zooplankton like copepods. Gray whales are unique bottom-feeders that scoop up invertebrates from the seafloor sediment.
Specialized Hunting and Toothed Whale Diets
The other main group, the Odontoceti, or toothed whales, employs a completely different feeding strategy based on active hunting rather than filtration. This suborder includes Sperm whales, Orcas (Killer whales), and various dolphin species, all possessing teeth used for catching and holding prey. Their diverse diets include schooling fish, squid, and marine mammals.
Toothed whales use echolocation, emitting high-frequency clicks that bounce off objects, allowing them to precisely locate prey even in deep, dark waters.
Sperm Whales and Deep-Sea Prey
Sperm whales, the largest toothed whales, dive to depths of 300 to 800 meters to hunt large, deep-sea cephalopods, including colossal and giant squid.
Orcas as Apex Predators
Orcas operate as apex predators, hunting cooperatively in pods. They take down fish like cod and herring, or larger prey such as seals, sea lions, and even other whale species.
Baleen whales filter feed using hundreds of keratin plates called baleen, which hang from the upper jaw. These plates act like a sieve to strain food from enormous gulps of water. This mechanism is optimized to capture dense patches of small organisms, contrasting with the pursuit-based hunting of their toothed relatives.
Whales as Ecosystem Engineers
The eating habits of whales have a profound impact on the entire marine environment, establishing them as ecosystem engineers. This influence extends beyond simple consumption and creates a highly indirect relationship with phytoplankton. Whales feed in deep waters or along the seafloor, but they must surface to breathe and rest.
While at the surface, they excrete massive plumes of nutrient-rich feces and urine, a process known as the “whale pump.” This fecal material acts as a fertilizer, containing high concentrations of essential micronutrients like iron and nitrogen. In the Southern Ocean, for example, whale feces can have iron concentrations millions of times greater than the surrounding seawater.
This release of nutrients into the sunlit surface waters, where phytoplankton thrive, directly stimulates their growth and reproduction. The fertilized phytoplankton blooms then support a larger population of zooplankton and krill, which the whales consume, completing a symbiotic loop. By moving nutrients vertically from the deep ocean to the surface, whales increase the overall productivity of their feeding grounds.