Marine Mammals as Sentinels of a Changing Planet

Earth Day 2026 marks record-breaking changes in our climate, particularly our oceans, where we’re seeing unprecedented warming waters, accelerated sea-level rise, and increasing acidification.

These changes will not only impact our oceans and the life that inhabits them but will continue to threaten the entire world through intensifying weather and ecosystem collapse. And for the species, such as sea otters and whales, that play a large role in regulating our ecosystems, these shifts are apparent.

The idea that marine mammals, or any species in the world at this given moment, are negatively affected by climate change isn’t new.

What’s less often discussed is the role many species play within the ecosystems they’re a part of and how those roles connect to broader processes. Also known as keystone species, these organisms hold ecosystems together, playing a disproportionately large role in maintaining biodiversity relative to their abundance, and in the world of marine mammals, there are two very important keystone species.

Sea otters are possibly the most well-known marine keystone species. Helping protect kelp forests and seagrass ecosystems, they increase carbon storage potential by up to 12 times.

Beneath the ocean surface, where you can see these adorable creatures eating, diving, and rafting, is an entire ecosystem of towering giant and bull kelp. These highly biodiverse kelp forests are home to sea otters’ favorite foods, including octopus, crabs, clams, and most importantly, sea urchins.

Sea otters consume massive amounts of sea urchins, equating to over 25% of their body weight daily. Despite the energy required to dive for and break into them, sea urchins provide a dense source of calories needed to survive in cold coastal waters.

By keeping sea urchin populations under control, sea otters help protect against sea urchin barrens (formerly populated kelp forests that have become bare to extensive urchin grazing). And when these kelp forests disappear, it’s not just the loss of habitat. Kelp plays a role in absorbing and storing carbon, with these ecosystems sequestering an average of 40 tons of CO₂ per 10,000 square meters annually, 20 times more efficiently than land forests.

But this balance is becoming harder to maintain, as climate change is impacting both kelp forests directly and indirectly through the sea otters that help keep these ecosystems intact.

Warming waters are already placing stress on kelp forests, particularly as marine heatwaves reduce the nutrient availability needed for kelp to grow and recover. In some regions, the warming has led to large-scale kelp loss, allowing sea urchin populations to expand unchecked. In these urchin-dominated ecosystems, they may appear abundant but are often starved with very little edible tissue, leading to limited prey availability for sea otters. This shift is forcing otters to travel farther and expend more energy to meet their already high metabolic demands. As a result, the very species responsible for keeping sea urchin populations in equilibrium are placed under increasing strain, allowing the whole system to fall further off balance.

While “whales” are not a single keystone species, many whale species play outsized roles within their ecosystems. Apex predators such as killer whales are known for influencing prey populations, leading to ecosystem balance, while baleen whales contribute to nutrient cycling through the “whale pump.”

The whale nutrient pump, also known as the “poop loop,” describes how whales transport nutrients from deeper waters to the ocean’s surface.

This process begins as whales dive hundreds of meters, consuming large amounts of prey such as krill and small fish. The whales then return to the surface to breathe, releasing nutrient-rich waste and redistributing essential elements such as nitrogen and iron, helping to support the growth of phytoplankton. These free-floating microscopic algae act as the foundation for marine food webs and absorb 40% of all CO2 fixed on Earth.

But just as warming waters are putting strain on sea otters and the kelp forests, whales and phytoplankton are feeling increasing pressure too.

Shifting ocean conditions are affecting the availability and distribution of whale prey. In some regions, this is changing where and how whales feed, forcing them to travel farther or adjust migration patterns in order to find sufficient food. Because the whale pump depends on whales consistently feeding at depth and returning to the surface, disruptions to feeding behavior and nutrient availability can begin to break down the system. With fewer nutrients being cycled into surface waters, phytoplankton growth declines, weakening marine food webs and the largest carbon cycling system.

As these pressures build, the very processes whales help sustain become less effective, further threatening our ocean’s health.

We often look to marine mammals as indicators of ocean health given how beloved, personable, and well-studied they are, but they are also part of the system that shapes our oceans and climate as a result.

As climate change continues to progress unchecked, the impacts don’t stop at directly affecting individual species, but place additional strain on the species acting to hold together their environments.

Thumbnail & Hero: Three sea otters playing in the Gulf of Alaska, courtesy of Kedar Gadge, Unsplash