This is part 3 of a 5-part continuous story about our most exciting everyday monsters. Check back weekly to read on.
Previous chapters can be found here:
He who fights with monsters should be careful lest he thereby become a monster. And if you gaze long enough into an abyss, the abyss will also gaze back into you.
– Friedrich Nietzsche
Part 3: Happy Homemakers
The ocean needs sharks in order to be healthy and thrive. Sharks play an important role as the stewards of marine ecosystems. Blah, blah, blah, yeah, yeah… sure buddy. I know.
We (educators and mega-nerds) loooove to tout this message, ad nauseam. We’ve said it so much that some people are even starting to believe it. What does it even mean? Why should we give a crap about our struggling but hopeful relationship with sharks? What have they done for me lately?
Sharks are top predators in their respective ecosystems. That makes having healthy populations of them invaluable both to the environments they inhabit, and to us. Top predators restore balance to the force maintain biodiversity (more different types of organisms), improve the health and limit the size of prey populations, and promote the health of ecosystems overall. OK, so what? What does all that mean? You probably already know how this works from a couple of cuddly examples. Despite their fuzzy charisma, wolves and sea otters are ecologically important predators whose ferocity would give any modern shark a pit in their spiral valve.
Everyone likes wolves, right? The Gray Wolf (Canis lupus) of North America, has had plenty more than their 15 minutes of fame. Through the extermination of the wolf’s prey, and direct eradication of the wolves themselves because of perceived competition with agriculture and livestock farming, the gray wolf had disappeared from most of the continental United States by about 1960. With their disappearance, the ecosystems that they previously inhabited, changed.
Ask yourself something about your own survival. “Self?”
“Would you/I go shopping at that grocery store across the street where they sell food a few cents cheaper?”
“Weeeell, what if there were a guy in the store that regularly wears water wings, a plunger on his head, and shoots random shoppers at least once a week?”
“Umm, y, ye, uhh, well, you’ve got Me there. No. I’ll pay a few cents more at the grocery store down the way.”
Often, just the threat of predation contains or controls the behavior of prey animals. In the United States’ Yellowstone National Park, someone saw fit to reintroduce the gray wolf. Without wolves, the local elk population had an excess of mommy and daddy elk who liked each other very much. The elk grown-ups passed on the fatal, sexually-transmitted disease that is life to their offspring, with no predators around to alleviate their burden. The elk also had a change of behavior. Elk and deer began to move into visibly open habitat like meadows and riparian habitat (rivers, streams, and associated wetlands), where they did what a whole bunch of big herbivorous critters do; they grazed. They grazed yummy soft-tissue plants. For those of you just tuning in; plants are both the basis and structure for most ecosystems. Changing the plants changes the ecosystem. It goes something like this: Grazing in new places prevented new growth of those plants which provided food and shelter for other species. No meadow plants, no food and home for critters that use meadow plants. No stream related plants like aspen and willow, no critters that use those plants. The number of different types of organisms that use that habitat began to dwindle. No wolves also meant that no one was competing with coyote (Canis latrans). While just as ambitious as the cartoons would have you believe, coyote aren’t very good at keeping the population of big ol’ elk in check. No more wolves also meant no more animal carcasses for coyote to scavenge. Without carcasses to scavenge, coyote were probably also great at predating on other smaller prey like beaver, who unfortunately ate and used water-loving plants like aspen. No wolf-kill carcasses, no food for scavenging birds and bears. No plants that grow near water, no fruits that come with them, less food for bears.
Sound like this is just cascading out of control? Weeellll, when an apex predator is removed from an ecosystem, and that ecosystem starts to come unraveled, sciency folks refer to that as a trophic cascade. OK, now for the good part.
In 1995 and 1996, wolves were reintroduced into Yellowstone after much hullaballoo. Some time passed, and a few mommy and daddy wolves who liked each other very much, passed life on to a few baby wolves, and they began doing wolfy (wolfish? wolfesque?) stuff together. Adding wolves back into the area, changed things again. The wolves didn’t eat thaaaat many elk or deer. But the threat of being eaten is pretty motivating for most animals (which, dear reader, is why we’re having this conversation). Elk began to move out of open meadows and river habitat and up into more forested areas that provided cover. Soft tissued plants in previously overgrazed habitat recovered, resupplying more different types of plants to those ecosystems. More and different plants, brings the organisms that use those plants. Beaver had food and wood to do beavery things with, like build dams. More beaver dams create more wetlands and change the flow of rivers and streams. More wetlands with healthier rivers and streams improves habitat for a wide array of important animals like trout and waterfowl. More riparian and meadow habitat means more homes and food for birds. With the reintroduction of wolves, coyote, bears, and scavenging birds had wolf-kills to eat off of as well. Now, almost 20 years later, scientists are showing that the change in the plants after the return of wolves has improved a critical component of the diet of grizzlies in the park by providing more berries.
Wasn’t that nice? By replacing this one apex predator, the whole ecosystem becomes more robust and healthier.
See? Trophic cascade.
But does it happen in the ocean, you might ask?
Ask it now.
Great question! Yes is does.
What if one animal had a super-duper-huge-o-riffic effect on a whole environment? What if there weren’t even that many of them? Don’t get your hopes up; I’m not talking about Godzilla. What if a creature were so vitally important that an entire ecosystem would be destroyed without them? What would fancy ecology type peoples call such a creature?
OK, OK, enough with all the questions! I give. That organism is called a keystone species. Ya happy now?
OK smarty pants, what would you call an insanely cruel and ill-tempered keystone species that lived in the ocean? Well, it’s hardly a guess since I already said sea otter once before. The sea otter’s keystone predator role makes this a shorter explanation than those complicated wolves. Also, the kind of people who regularly wear sea otter t-shirts are a tiny bit less odd than that rowdy wolf t-shirt rabble. In this case the “plants” (algae), are kelps. Big, fast-growing productive kelps provide structure and food for thousands of different types of other plants and animals in the near-shore ocean. Kelp is eaten by little purple pincushiony invertebrates called sea urchins, which graze it away from the rocks that it needs to hold onto. Many of the animal species that use the kelp forest for habitat are commercially important fishes. Several of those use the kelp to grow up in, and then disperse to other habitats when they are big enough. Otters eat sea urchins. Urchins are so full of reproductive organs, that they are basically well defended, angry purple gonads. Without otters, mommy and daddy urchins who like each other very much do what all organisms do, and pass on their genes to so very many offspring. When urchin sexy-time goes on for too long without something eating them, the entire kelp forest habitat is lost. Left unchecked in nature, they will breed and eat to the point that they create what is called an urchin barren; where the only thing left on the seafloor is urchins. We hunted sea otters for their fur, so much that we thought they were extinct at one point. They weren’t. We have documented the return of the kelp forest habitat and all of the species that need it for food and shelter along with the sea otter.
So, what does all this have to do with sharks?
The ocean is a difficult place to make the kinds of relationship distinctions that ecologists do on land. There are fewer barriers in the vast liquid interconnectedness that is our world ocean. When animals have been documented crossing the waters of the entire planet, it becomes harder to see the effects of removing apex predators in a single place. That said, we do have a pretty good example. On the east coast of the good ol’ US of A, we once had abundant and thriving marine ecosystems of all sorts. We came, we fished, we built cities, we kept fishing…we don’t have thriving marine ecosystems of all sorts. In places like Chesapeake Bay, we had plants, and the organisms that use them for food and habitat. We had an economically important shellfish fishery for scallops and oysters. Mmmmmm, yummy, yummy mollusks. The plants that provide the structure and food, as well as oxygen and other important nutrients, are known as eelgrass. Bivalve (two shells) shellfish like scallops, live in the muddy bottoms in the shelter of eelgrass. Bivalves filter tremendous volumes of seawater every day, which helps to clean it out of pollutants from runoff, as well as filtering out the plankton that they eat. Healthy shellfish populations improved the quality of the water and supported a shellfish fishery. The eelgrass of course, provided vital habitat for juvenile fishes like shad and herring that needed it for shelter until they grew up and dispersed into different habitats. Just like the kelp forest, eelgrass provides habitat for thousands of different species including juvenile blue crab. Is this all sounding familiar yet?
After fishing out the big sharks from the east coast waters, either through fishing methods that involve a lot of bycatch like long lines and gillnets, or through targeted shark fisheries, the ecosystem changed. In the absence of large predators, a sizeable population (for which we had no fishery) of adorable cow-nosed rays began foraging in the eelgrass for their preferred shellfish food. I don’t blame them. It would take very little to convince me to rummage face-first in the mud for fresh scallops. The mechanical disturbance of foraging rays to the eelgrass, uprooted those plants. The habitat for all of the invertebrates and fish that need it for shelter was lost. By that same token, the rookery habitat for the juvenile fish for which we had our own fisheries was lost; damaging the fisheries and our economy. Our fishery economy was further damaged by the loss of shellfish to ray predation. Without shellfish to filter the water, pollutants were retained and plankton bloomed, causing a depletion of oxygen and creating dead-zones and poor water quality.
So, to recap, losing big sharks leads to damaged fish and shellfish economies, degraded habitat and lowered biodiversity through the loss of habitat-providing eelgrass, and we are left with algal blooms, dead-zones, and whole lot of adorable cow-nosed rays.
Seriously though, they’re really cute.
Since the oceans are so thoroughly interconnected, and it is so hard to find examples of interactions within discreet ecosystems, Chesapeake Bay becomes an important highlight. Knowing how the removal of big sharks from this ecosystem damages it, and our own fisheries, begs the question of how removing big oceanic species that travel the world may affect broad-scale ecosystems across the globe. By fishing for sharks, aren’t we damaging future oceans and fisheries for people all around the planet?
People recognize that it is important to protect entire ecosystems, and we already have great evidence that it works well. Based on successes from around the world, California has instituted a series of Marine Protected Areas (MPAs) in order to protect entire ecosystems. Instead of trying to manage one species at a time in a game of depleted fishery catch-up, MPAs protect the whole system in the hopes that they will recover to the point of producing enough fish to spill over into non-protected areas. Guess what? It works! We have example after example of success stories from MPAs around the world and we’re starting to see their success in California. So how do we handle sharks? No matter how politely you ask, most freedom-loving sharks won’t stay within the delineated boundaries of our legal system. For larger migratory species, we have to take a different approach in order to ensure the health of the ecosystems that they influence. We’ll get to that next week.
I am taking the liberty to simplify things for the sake of education here. Nature is infinitely complex which is why it is so satisfying to study. Sometimes it helps to clear out some of the background noise in order to elucidate a few of the more important processes. Some of you may pipe in at this point with comments about scientists disagreeing with each other over various details of these examples. Scientists do argue. For those of you non-sciency folks out there, science is made of argument. That’s how you know it’s good. Scientists continually attempt to disprove each other and themselves. That means that when the dust finally clears, settles, and probably collects many more years of dust, the resulting information that science relates to the public is pretty damned accurate. If you didn’t already believe science, you wouldn’t partake of modern medicine, agriculture, or transportation; and you wouldn’t be reading this.
Scientists are sure that the ocean needs sharks in order to be healthy. Scientists are sure that we need healthy oceans to be healthy ourselves, and for our children to survive and to live well. Scientists are sure that we need sharks.
The value in preserving top predators is that it allows entire ecosystems to thrive to the benefit of us all. It’s for everyone’s good that we care for sharks. Just because the relationship between us, sharks, the health of the ocean, and the health of us, is complicated, does not make it any less true. Once we understand and appreciate that sharks are apex predators necessary for maintaining the health of larger ecosystems, we may become beneficial monsters ourselves.
Sharks are in trouble because we catch them for a variety of wasteful uses. Shark products like cartilage or oils are sold as homeopathic remedies. Often these are used to treat things as severe as cancer, under the mistaken idea that sharks don’t get cancer. This is akin to eating the heart of your conquered enemy to assume his powers and wealth. There is no scientific basis for using these products to treat human disease. Sharks are also hunted just for their fins to make soup. The demand for this once-rare delicacy has grown with an emerging Asian middle-class who views eating shark-fin soup as a symbol of wealth. The fins themselves do not add flavor or nutrition to the soup. We are affecting fisheries to take the fins from the stewards of those large ocean ecosystems, in order to make a soup that gets its flavor from chickens. There is a trade-off between using individual sharks in the short term, and valuing the benefit of having them to contribute to the health of the oceans in the long-term.
By understanding the value in protecting sharks and doing something about it, we protect the fragile sea; monsters and all; especially us.
Tune in next week when we reveal how to put the spice back into our love life with sharks.