Marine mammals can serve as indicators of changes in their ocean environment. Despite being resilient animals, rising ocean temperatures, ocean acidification, and rising sea levels are just some aspects of climate change that will impact marine mammals, their food sources, and their homes.
Rising Sea Levels
Many species of seals and sea lions rely on beaches to rest, give birth and nurse their pups. Warming water temperatures, as well as melting land ice, have contributed to rising sea levels around the world. In turn, marine mammals are losing an important habitat on beaches. In some cases, like in Hawaii where the islands are very low lying, the critically endangered Hawaiian monk seals have already lost an estimated 50% of their historic breeding beaches to rising seas. For other species, like the Northern elephant seals in California, as the water invades their breeding beaches, it makes the pups more prone to exposure to large storm surges and increases the likelihood of young pups being separated from their mothers during their first month of life.
Warming Water Temperatures
Just as humans have preferred temperature ranges, so do many of the animals that call the ocean home. While marine mammals have been shown to be quite resilient to changing ocean conditions, the food that seals, sea lions, whales and dolphins depend on has been shown to change locations due to warming water. In the presence of warm water, schooling fish such as sardines and anchovies, favorites for California sea lions, tend to dive deeper and further offshore to find colder water. This extra distance means that sea lions must spend more energy traveling and hunting than before. In 2015, we saw that record warm water temperatures in California resulted in thousands of sick sea lions on the beach as mothers left their pups early due to the harder foraging environment and pups struggled to dive deeper and farther in search of food.
More Acidic Water
Similar to water temperatures affecting fish populations, particular types of plankton have been shown to behave differently due to changing water temperatures or ocean acidity. As water temperatures continue to warm, and the ocean becomes more acidic, we anticipate seeing more harmful algal blooms. One particular diatom, Pseudonitzchia australis, responsible for producing a toxin called Domoic acid toxicosis, is one that could have dramatic effects on marine mammal populations. First identified in 1998 by The Marine Mammal Center, this toxin accumulates up the food chain and can cause seizures, disorientation and brain damage at animals that feed at the top of the food chain. In 2015, with record warm water temperatures, the largest algal bloom in history was observed off the west coast of the United States and resulted in over 200 sea lions suffering from domoic acid toxicosis and also shutting down fisheries, such as Dungeness crab and razor clams, to human consumption.