Part II: The Ecology

Hello again!

Hello, science enthusiasts! Hello, animal lovers! Hello, conservationists! Here's your third stream of bubbles containing interesting information from this little corner of the California coastline. I'm Shelby, and I'm here to offer some insight on the health and function of some of the most important features of Northern California's coastal ecosystems.

In the last post I outlined the series of unfortunate events that led to the Sonoma and Mendocino County kelp forests turning into urchin barrens. It's easy to call this timeline just a cluster of bad luck, and I suppose it could be, but climate change is definitely the main culprit. Now you know how everything happened, you might be asking why it happened. Why did the ecosystem change so radically? I briefly explained this in the previous post, but I'd like to take the time to explain the actual ecology behind it. It's important to know how systems work in order to best assess how to help set them back into alignment.

The first and probably most important point to touch on here is what happens when a keystone species is removed from a food web.

Side note, I use the term “food web” instead of “food chain” mostly because it's more accurate. “Food web” is a more broad term referring to the total interplay of energy exchange between organisms living in a community together. “Food chain” only refers to specific interactions in one area of a food web. Even though it may seem like I'm only focusing on a narrow section of the kelp forest food web, the effects of the changes ours have undergone are being felt throughout the whole web. If I give attention to every part of the kelp forest food web being affected, we'd be here all day.

Here's an example of a marine food web. Lots of interconnected interactions; it's more complicated than a food chain. Source: https://www.researchgate.net/figure/Food-web-of-shallow-water-and-deep-water-ecosystems-of-the-western-rock-lobster-showing_fig4_255590014 

So, what is a keystone species? I'm sure a lot of you have heard this term, either in passing or at some point in your education. But there's no harm in a little reminder, right? It certainly could be considered one of the more widely known terms in ecology. 

I didn't even think of sharks as a keystone species, but there you go. Kind of obvious when you think about it. Source: http://ib.bioninja.com.au/options/option-c-ecology-and-conser/c1-species-and-communities/keystone-species.html 

A keystone species is a species that, through both their presence or absence, has a disproportional effect on their community. Indeed, they usually influence the entire structure of the food web. This animal can be a predator, an herbivore, or even a mutalist; the interactions revolve around what the animal eats. Without the presence of the keystone species, their food source has a tendency to grow out of control and out compete the rest of the species in the community. With the keystone species presence, their food source is kept in line and more species are allowed to flourish. This allows for biodiversity, something scientists agree is pretty much essential for an ecosystem to function healthily.

You're probably familiar with this one; the Yellowstone food web when wolves are present vs. when they're absent. It's a pretty big difference. Source: https://www.britannica.com/science/trophic-cascade

The second point to talk about here is the concept of a trophic cascade. This is directly related related to keystone species, as trophic cascades happen as a direct result of a keystone species being removed from its food web. An animal's position in its food web is known as its “trophic level”.Trophic cascade refers to a series of sequential, reciprocal changes that ultimately alter the structure of the ecosystem. If a predator is removed, prey increases, then plant decreases, others that feed on that plant decrease (in the simplest of terms). This can happen if an herbivore is removed too; whatever plant it feeds on will out compete whatever other plants are in the community, which removes a food source from other herbivores. The keystone herbivore's predator might decrease, or it could move on to a different herbivore, which will decrease and lead to another plant increasing. Rinse and repeat. If it's a mutualist that is removed, a situation that isn't given nearly enough attention, it can be dramatic too. It's what happens if bees are removed; lots of plants go without pollination and die off.

Here's another example of a trophic cascade, with direct reference to how it's something we have a tendency to cause. Source: https://www.researchgate.net/figure/Top-down-control-or-trophic-cascade-in-the-food-chain-for-four-trophic-levels-in-a_fig4_305420537 

The last term I'd like to talk about is the alternative stable state theory. It states that the conditions of ecosystems, or states, can shift between different sets of structural characteristics. These states are separated by "ecological thresholds".These are the points at which either a small or large change can kick off a series of rapid changes in an ecosystem The shifts between these states are not gradual but abrupt, and once a shift happens, it is very, very hard to shift back thanks to the stability of the alternate state (https://www.biology.lu.se/research/research-groups/aquatic-ecology/research-projects/alternative-stable-states). Examples of this theory in action includes: a kelp forest changing into an urchin barren, and a coral reef turning into an algae reef.

This is what is happening right now, but I couldn't find a picture with a reverse order. Just read it right to left for the correct effect. Source: https://www.flickr.com/photos/santamonicabaykeeper/7416849358 

If you take these three ideas into consideration, you can put together a pretty cohesive picture of how Sonoma and Mendocino County's kelp forests turned into urchin barrens, and why it's become such an arduous task to try and get things back to normal. Remember that “perfect storm” of events I outlined in the last post (Catton, Rogers-Bennett, 2016)? 2013 brought us the beginnings of a condition called sea star wasting disease. This is a usually fatal syndrome, starting first with lesions then transitioning to fully dissolving the flesh. Despite the rigorous research being conducted on the disease, its cause is still unknown.

This poor sunflower star is still in a fairly early stage of the disease, but I think you can see its arms are starting to fall off on the right. Source: https://phys.org/news/2016-10-survey-impact-sea-star-disease.html

Wasting disease is still working in full force and is responsible for the massive population loss of our sunflower sea stars. The sunflower star acts as the primary keystone predator for Sonoma and Mendocino kelp forests, so its loss has caused a top-down trophic cascade; the decrease in sunflower stars has lead to an increase in purple sea urchins, which has lead to a decrease in kelp coverage, which has lead to a decrease in the number and health of red abalone and other herbivores in the food web. The urchins decimating the kelp has caused the kelp forest ecosystem to shift to its alternative stable state, the urchin barren.

See? This is too big a job for just a few sea stars, especially when those stars are sick. Source: https://www.sfu.ca/sfunews/stories/2016/sea-star-death-triggers-ecological-domino-effect.html

The reason it has been so difficult for the urchin barrens to change back to kelp forests (as the alternative stable state theory says it would) is because without their primary predator present, the purple urchins are free to graze on any algae as it attempts to grow. This is especially damaging to bull kelp, which used to grow in massive abundance. Bull kelp is a perennial algae, meaning it has to complete its life cycle in one year. If it doesn't get past the immature stage, that means the loss of a generation. The urchins normally feed on adult kelp, attacking the stipe (base) and chewing through it until it breaks away from the hold fast. Without adult kelp to eat, the urchins have to forage for something else and end up eating immature kelp before it has a chance to reach maturity. No kelp can grow if it isn't given a chance.

The kelp are basically under siege at this point, and they're losing the battle. Source: https://cdfwmarine.wordpress.com/2016/03/30/perfect-storm-decimates-kelp/

Understanding these ideas is an important tool when evaluating the state of a biological system. The better versed we are in the background principles, the better we are in formulating a plan. I've explained the ecology behind these phenomena, now the next step is to explain the physiological aspects of the animals affected by them. But that will be for next time. I'll warn you now; it might get heavy. Learning how these animals are suffering as a result of these changes was a big wake up call for me.

This is from a site about poaching, but it's also an accurate image of what things look like down there right now. Source: https://www.kzyx.org/post/chasing-abalone-poachers-north-coast#stream/0

Stay curious.

"Sea" you next week!