Seals are a diverse group of semi-aquatic marine mammals found across the globe, from the frigid polar regions to temperate and even some tropical waters. These fin-footed carnivores spend most of their lives in the ocean but come ashore to breed, give birth, and rest. Their streamlined bodies and powerful flippers allow them to dive to significant depths and travel long distances in pursuit of food. As integral parts of marine environments, seals play various roles that influence the health and stability of the complex ocean ecosystems they inhabit.
Balancing Marine Ecosystems
Seals function as predators within the marine food web, helping to regulate the populations of their prey. Their diets vary by species and location, but commonly include fish such as cod, herring, and salmon, as well as squid, mollusks, and crustaceans. For instance, the crabeater seal primarily consumes krill, while leopard seals are apex predators that hunt penguins, seabirds, and even other seals. By preying on these species, seals contribute to maintaining ecological balance, preventing the overpopulation of certain species that could otherwise disrupt the ecosystem.
Food Source for Larger Carnivores
Beyond their role as predators, seals also serve as a food source for larger marine and terrestrial carnivores. They provide energy and nutrients to species higher up the food chain, including polar bears, orcas (killer whales), and large sharks like great whites. Polar bears, for example, rely heavily on seals for their calorie-rich blubber. The presence of seals is thus important for the survival and population health of these apex predators.
Recycling Nutrients
Seals contribute to the recycling of nutrients within marine environments through their waste products and decomposition after death. Their feces and urine release nutrients back into the water column, which then become available for phytoplankton and other primary producers. These primary producers form the base of the marine food web, supporting a vast array of marine life. Additionally, when seals die, their carcasses decompose, releasing organic matter and nutrients back into the ecosystem. This process benefits scavengers and decomposers, further facilitating the cycling of essential elements that sustain ocean productivity.
Sentinels of Ocean Health
Seals are recognized as bioindicators, providing insights into the overall health of marine environments. As long-lived animals that occupy high trophic levels, their health, reproductive success, and population trends can reflect broader changes in the ecosystem. Monitoring seal populations can reveal impacts from pollution, such as toxin bioaccumulation, shifts in prey availability, and the effects of climate change, including sea ice loss affecting Arctic species dependent on ice for breeding and foraging. Scientists attach sensors to deep-diving seals, like elephant seals, to collect data on ocean temperature and salinity, providing valuable information on hard-to-reach areas and helping track changes like melting glaciers. Changes in seal populations can signal ecological shifts that warrant further investigation, making them important natural monitoring tools.