A long delay from when promised, but I'm happy to have gotten this off the ground all the same.
Somewhere in the Alaskan ocean wilds, a sleek mammal glides through the salty water surrounding an expansive forest of kelp. It is a sea otter, and doing what sea otters do, it is swimming and it is eating. It spots a small pink urchin, a creature resembling the result of a forbidden encounter between a porcupine and a Tribble. It pulls its prize off an algae covered boulder, it surfaces, and using its belly as a resting surface for the prey, it begins to feed.
That this interaction may help sustain entire aquatic ecosystems was a notion first suggested by the ecologist James Estes in the 1970s. While boating through the Aleutian islands in southwest Alaska, he noticed stark differences in habitat between areas occupied by urchin eating sea otters and those without. In near shore habitat without sea otters, kelp forests were decimated by great numbers of kelp grazing urchins. Without the kelp forest, the faunal and floral community was undiverse and desolate. Contrastingly, regions with sea otters had much lower urchin density and supported a great number of wildlife species. By feeding on plant eating urchins, the sea otter was causing an aquatic trophic cascade, and thereby increased the ecological integrity of an ecosystem.
As sea otters recolonized regions that they had been extirpated from by fur traders of the past, Estes and his team documented a resurgence of these healthy kelp forests.
However, several decades later, it was apparent that all was not well with the Alaskan sea otter population, and they pinpointed a culprit.
Starting in the early 1990s, Estes and his team noted a marked increase in the number of sea otters killed by orcas in western Alaska. In areas inaccessible to orcas, otter populations were stable. In locations with orcas, sea otter numbers plummeted, which brought a corresponding increase in urchin numbers and its associated ecological damage.
What prompted this relationship, when both species shared the same habitat for decades prior? Estes suggested that declines in sea lions, the orca's staple food source, caused a shift in feeding behavior.
However, this story may be deceptively simple. While the link between otters and kelp forests in Alaska seems strong, others have searched for similar links in otter occupied habitat in coastal Washington and California, and found the evidence lacking. Otters are only one of many forces that can influence kelp beds, including land use, temperature, ocean acidity, and others.
Ecology is an incredibly complex science, and causal factors can vary dramatically over space and time. However, the tales it tells are fascinating to me as a scientist, and I hope that through this prose it can be made fascinating to you the reader as well.
Next up: no idea. But it'll be exciting.