How sea otters save kelp forests – the mysteries of aquatic ecosystems

From a biological perspective, the adorable sea otters play a crucial role as a keystone species, whose presence in the ecosystem significantly impacts the health of kelp forests. However, a recently published study by North American scientists sheds new light on the processes governing the pace and extent of underwater regeneration.

Voracious sea ptters

Also known as kalan, sea otters (Enhydra lutris) are, on the one hand, the largest species in the weasel family, yet on the other, the smallest marine mammals. Unlike seals or whales, they are not protected from the cold by a layer of fat but rather by exceptionally dense fur, considered the thickest in the animal kingdom. Found in the coastal waters of the northern Pacific Ocean, they feed on sea urchins, mollusks, and other crustaceans found on the seabed.

It is their particular fondness for spiny sea urchins that makes sea otters exceptionally significant for coastal ecosystems. Sea urchins feed on the lower parts of kelp, leading to its rapid decline. In the absence of predators, they can quickly destroy vast areas of kelp forests, triggering a cascade of negative ecological consequences. As a result, the seafloor begins to resemble a barren wasteland.

Research on kelp forest recovery

The balance between sea urchins, algae, and sea otters has been a subject of scientific interest for decades. Observed destruction of underwater kelp forests prompted ecologists to attempt the reintroduction of sea otters in areas where their populations had disappeared. This species is endangered due to oil spills, poaching, and orca attacks, which limit their numbers.

The reintroduction of sea otters to the coastal zone near Vancouver Island in Canada and San Nicolas Island in California turned out to be a highly beneficial impulse – kelp forests indeed began to regenerate, resulting in the restoration of entire underwater ecosystems. However, the speed and extent of these changes varied across different regions. Scientists from the University of Colorado Boulder sought to understand the reasons behind these differences by analyzing 30 years of observational data from California and the Canadian province of British Columbia.

The importance of inter-species relationships

A study published in the journal PNAS, led by Ryan Langendorf from the CIRES Institute for Environmental Research, focused on comparing the dynamics between species during the recolonization of habitats by sea otters. In British Columbia, positive changes in the ecosystem occurred much faster – sea urchin populations decreased, and kelp forests began to recover intensively. However, in Southern California, the trophic cascade triggered by the return of sea otters was significantly weaker.

To better understand the mechanisms of these underwater changes, scientists developed an innovative model in the form of a documentary film, illustrating interspecies relationships in both locations over the past 30 years. The analysis revealed that competition among different types of kelp, sea urchins, and other underwater species in California was so intense that it suppressed the impact of sea otters on the ecosystem. This complex network of interactions within the food chain appears to minimize the significance of keystone species.

These findings mark a breakthrough in ecological studies since, until now, it was believed that inter-species interactions were static and that their rules did not change depending on species populations. However, the dynamics within ecosystems appear to be more complex than previously suspected, and with them, the role of keystone species may also shift.

The decline of kelp forests remains a major challenge. Apart from sea urchins, it is also exacerbated by climate change, water pollution, and the activity of fish and mollusks. While sea otters cannot solve the problem globally, under favorable conditions, they can significantly improve the health of local ecosystems.