Many people wonder about the diet of seals, particularly whether tiny plankton forms a part of their sustenance. Understanding what seals consume reveals much about their biology and their place within marine food webs.
The Truth About Seals and Plankton
Seals, primarily belonging to the group known as true seals or phocids, do not consume plankton as a main food source. Their physical characteristics and feeding mechanisms are not designed for filtering microscopic organisms. Seals possess sharp, pointed teeth for grasping and tearing larger prey. Their molars are adapted for crushing shells and other hard-bodied prey, not for sieving tiny particles.
Despite this, there are a few specialized exceptions among seal species that incorporate zooplankton, such as krill, into their diets. The crabeater seal, for instance, primarily feeds on Antarctic krill, utilizing uniquely shaped, interlocking teeth that act like a strainer to filter these small crustaceans from the water. Leopard seals also employ a similar filter-feeding method for krill, alongside their broader predatory diet. Ringed seals and Baikal seals are also known to consume zooplankton. However, these adaptations are distinct from the widespread filter-feeding observed in animals like baleen whales.
What Seals Really Eat
Seals are carnivores, meaning their diet consists of other animals. Their primary food sources include a wide variety of fish, such as cod, herring, salmon, flounder, hake, and sand lance. Beyond fish, seals also consume cephalopods like squid and octopus, as well as various crustaceans including shrimp and crabs.
The specific diet of a seal can vary depending on its species, geographic location, and the availability of prey. For example, elephant seals primarily hunt fish, squid, and octopus, with northern elephant seals also consuming rays and sharks. Leopard seals have a diverse diet that includes fish, penguins, seabirds, and even other seals, in addition to krill. Seals are adept at foraging, often using their sensitive whiskers to detect the movements of prey in the water, even in low light conditions.
Plankton Eaters in the Ocean
Plankton represents a fundamental component of marine ecosystems, forming the base of many aquatic food chains. This diverse group includes phytoplankton, which are microscopic, plant-like organisms that perform photosynthesis, and zooplankton, which are tiny animal-like organisms, including small crustaceans and larval stages of marine life. Many marine animals have evolved specialized filter-feeding mechanisms to consume these abundant, small organisms.
Baleen whales are prominent examples of animals that feed on plankton, using baleen plates in their mouths to sieve vast quantities of water and trap tiny prey. Species like blue whales and humpback whales primarily consume krill, a type of zooplankton, using this method. Other filter feeders include certain sharks, such as whale sharks and basking sharks, which strain plankton from the water as they swim. Various invertebrates, including bivalves like oysters and clams, also filter microscopic food particles from the water column.