Almost as if they were trees, wavy lines of forest green and earthy brown shoot upward, reaching out to the distant rays of pearlescent white near the surface. Small turquoise bubbles make the long ascent to this mysterious light while anchovies dive together in large schools (Figure 1). As they weave in and out of the submerged forest, their senses relax, grateful for the cover from larger predators.
Figure 1. California fishery sustained by aquatic forests.
Even larger animals find themselves enjoying the shelter, namely the elegant harbor seal shifting comfortably along the gleaming stalks, which extend their blades upwards of 200 feet to touch the sun (Figure 2).
Figure 2. A harbor seal weaving through a submerged forest.
A closer look gives a kelp forest, consisting of giant kelp, Macrocystis pyrifera, and bull kelp, Nereocystis leutkeana. With long, blade-like arms held afloat by pneumatocyst air bladders, both of these phenomenal producers appear to defy gravity and the force of the translucent Pacific Ocean above as they call out to the sun’s rays for an opportunity to photosynthesize (Figure 3).
Figure 3. Kelp anatomy, note the gas bladders are the aforementioned pneumatocysts.
Stretching along the length of coastal California and Oregon, submerged kelps have come to be considered a foundational species for their ability to create sustainable habitat to support a wide variety of organisms.
However, these Eastern Pacific kelp forests are no longer a guarantee, becoming an anomaly to what was once a normality in these waters. In fact, phenomena occasionally referred to as ‘zombie forests’ are becoming more frequent.
To understand this change, we must travel back to over a century ago.
Figure 4. Rare 2021 Oregon Coast otter sighting shocked locals and brought huge media attention.
The year was 1907, a critical point in the history of Oregon. Along the coast of Newport Beach, the desolate splashing sounds of the very last sea otter echoed dully as the animal’s body went limp, the illustrious hunter collecting his catch to trade the pelt in the market for sizable profit. ‘What a prize,’ he must have thought. For the warmth such pelts conferred by containing up to a million follicles per square inch, Enhydra lutris sp. was incredibly valuable to his consumer base. Nevertheless, little did he know, this was the last otter he would ever catch and that Oregon would see for a very long time (Figure 4). It has been since this time that the kelp forests’ days grew numbered.
In fact, one of the only animals to consume sea urchins, sea otters had the capacity to control the whole layout of the ocean floor (Figure 5).
Figure 5. Sea otter enjoying a purple urchin dinner.
Figure 6. A zombie forest in the Pacific dominated by sea urchins.
In their absence, sea urchins ruthlessly demolished the kelp, preying particularly on bull kelp. A former haven for many fish, invertebrates and aquatic mammals as a source of shelter and food, the replacement of kelp with ‘zombie forests’ of urchins is a horror story well-known in most coastal parts of Northern California and Oregon (Figure 6). One Monterey Bay photographer, Brandon Cole, described the once-picturesque scene as a ‘ghost town’ and an ‘atomic wasteland.’
Figure 7. Decline of kelp from global warming and loss of natural predators of urchins has left the abalone fishery destroyed.
It is here that the urchin barrens are filled with purple, spiky animals that have minimal nutritional value and the entire absence of coverage means other animals must seek new niches to survive. The reduced environmental carrying capacity for these migrating animals, however, typically results in populations of species as a whole growing threatened or endangered. This is especially since more sessile or benthic creatures are unable to easily move to a new location to increase their survival prospects: this is, for instance, demolishing the once prominent abalone invertebrate fishery that relied on the kelps (Figure 7).
Figure 8. Presence of sea otters and rehabilitation efforts in Central California has restored and preserved kelp forests.
Fortunately, rehabilitation efforts of the otters, particularly in Central California by Monterey Bay Aquarium and other interested groups, has allowed for the re-establishment of their populations. In these regions of California, kelp forests are managing substantially better as the otters feast on the bounty of urchins (Figure 8).
However, Northern California and Oregon continue to suffer as northbound migration has so far not been easy for sea otters since it would involve them crossing through territory predominately filled with great white sharks, which tend to take exploratory bites of the mammal. Though, a new sense of hope was reignited in late November 2021 with a rare sighting of a sea otter that had made its way successfully back to Oregon.
It is truly miraculous how one animal can redesign an entire ocean floor despite mostly living on the ocean surface, but this is no challenge too great for the sea otter. With some human help, the sea otter can help to bring back kelp forests and the astounding oceanic flora and fauna that once characterized Eastern Pacific waters.
Bridget, I’m once again amazed by how much work you put into providing sources, images and links for further reading. This is an interesting and complex part of the ecosystem, and I didn’t realize how large of a role the kelp forests played in underwater fauna.
My question is, what are the benefits of urgence? It seems like when in too high of a population, urchins take out the kelp forests and that otters need to keep them in check. But it seems like there should be at least a purpose for them in the first place besides just feeding otters. What is that?
Also, urchins are covered in spikes. Is that a defense mechanism? And does that have anything to do with how they destroy the kelp forests?
I think a blog post on the plasticity and resilience of natural environments that have previously been destroyed by human actions would be interesting. It would entail commentary on how much of what was lost could be obtained again.
Here’s how it could be applied to this issue.
When do you think the urchin population near Oregon will be low enough for kelp forests to truly thrive? Do you ever think they will fully grow back? What would be your recommended solutions for decreasing the urchin population besides just adding sea otters?
Douglas, thank you for all of these insightful questions about the functions of sea urchins. Next week I will write a blog post answering them!
I just have to say, the first picture taken by Lowell Richards at the beginning of your blog is priceless – the way the otter is waving their hand is the best, and the attitude is so good. Every time I read one of your blogs, I’m always fascinated to learn about human practices and their effects on nature. Sure, we hear about global warming and the macro-scale activities humans do to survive; looking at things through a smaller lens and looking at our effects on one population is important, just the same. In grade school, I remember learning about sea otters and their place in the western market during the 1900s – trappers littered the west and caught everything in their sights to make fur accessories. Honestly, I thought that after that era in history was done with, and the otters didn’t exist in that area of the United States anymore, the ecosystem would not be so affected. I was very wrong. On initially crossing my mind, sea otters as a keystone species didn’t make sense, but after detailing how they regulate sea urchin growth and prevent ‘zombie forests,’ I changed my opinion on the matter. Suppose you oversaw helping sea otters migrate to California and Oregon today. Would you try to catch and release otters from the north in your targeted areas or continue to see if they can bypass the great white’s blocking their path? Is there any hope of reintroducing the other organisms that lived in the ‘pre-zombie forests’ anytime soon? As always, I’m excited for next week!
Hey there Joseph! I’m glad I could share a bit about otters and their importance. I learned a lot as I wrote this because initially I had the same thought as you. Sure, they’re adorable, but what value do they really confer to our world? Turns out they’re adorable and also trash compactors for kelp forests. If I had it my way, I think it would be better if there were more monitoring and introduction efforts near coastal Oregon before we introduce any more otters to California’s northern reaches. That way, the best fit individuals of the central California population and the Oregon population could converge and survive in Northern California to a sizable enough degree to make the great white issue less problematic. I can write about this another time too, but there are efforts in Northern California and Oregon waters to also bring back some starfish species that eat urchins! The starfish have been wiped out by disease caused by warmer waters from climate change, but certainly that is also a future possibility. To answer your last question, I think once we start thinking about ways to actually restore kelp forests, many migratory species will be able to return naturally. However, some invertebrates like abalones that I mentioned are pretty immobile in their lifetimes, so we would likely have to make efforts to restore populations like that externally. Certainly then comes the question as to what species we should prioritize and whose money we are using to do this, but these are all things I hope we can figure out in time.
Reading your blog makes me dislike humans (although as Douglas pointed out on my blog, I am a human myself). But as I mentioned on my piping plover post, I’m happy that humans are realizing the damage they have caused on the animal population (sea otters in your blog) and are trying their best to reverse the negative effects of human activity. This post really reminded me of how introducing predators of the species causing damage (like the wolves in Yellowstone that you wrote about on your first post) can help revive the landscape. I often think of the prey as the critical animals in an ecosystem, but it might just be the opposite. I think it’s also funny how humans didn’t take advantage of the exploding sea urchin population. In Japan, sea urchin is a popular but expensive food, often found on sushi or in sashimi plates. I would have made a sea urchin business (this is probably the type of human thought and action that destroy natural ecosystems). I also LOVE otters, and always go visit them in aquariums if they are there. Sea otters eat their food by banging them on rocks that they keep in their stomach pouches. But they don’t use a random rock; they have a favorite rock that they use for all meals. And if they lose that special rock, they can’t eat until they find a new favorite rock. Aren’t they so adorable!? I look forward to reading your next post!