DIVERSITY IS GOOD
IN DECEMBER 2002, the Scripps Institution of Oceanography hosted a conference, funded by the Sloan Foundation, on the “Knowns, Unknowns, and Unknowables of Marine Biodiversity.” One of the goals was to assess the value of biodiversity and the cost of not knowing how many species there are and what they all do in nature. Through the first two days, scientist after scientist debated two conflicting philosophies. One contingent said the most important thing to do was to acquire new knowledge, while the other wanted to find ways to use the knowledge we already had to reverse the loss of marine biodiversity. The tension frustrated some participants, who were not used to thinking about the unknowable. But the most frustrated person in the 200-person auditorium may have been Natasha Loder, a reporter from The Economist, who finally stood up and said, “I have been sitting here for two days. I’ve heard many of you say that ocean biodiversity is very important, that we need to conduct more studies…but I have not heard anyone say yet why biodiversity is important. I would love to go back to my desk and write a piece for my magazine, but you guys are not helping me.”
Boris Worm—who by that time had produced some of the most important studies on marine conservation—and I were sitting together just a few rows in front of Loder. We looked at each other and almost simultaneously said, “This is ridiculous. We need to find a clear and definitive answer to that question.”
Boris and I decided to move quickly. We applied for a grant at the National Center for Ecological Analysis and Synthesis (NCEAS), a wonderful institution associated with the University of California, Santa Barbara. NCEAS is like catnip for ecologists. If your application is successful, you will be funded to conduct a series of workshops with colleagues of your choosing, inviting them to discuss and analyze an issue of your choosing, and working together to come up with a synthesis of your ideas. Working groups typically last two years and result in the publication of a major scientific paper. The good news is that NCEAS decided to fund us, and thus we put together a group of mostly young marine ecologists, mostly old friends, and started in earnest.
Meetings at NCEAS are so much fun. A group of passionate scientists get together for three or four days at a time a couple of times a year. Our daily schedule consisted of presentations and discussions from nine in the morning to noon. Then we walked outside to have lunch, and were back in the conference room at 1:30 p.m. At 5 p.m., our brains full of ideas, we moved to the James Joyce Pub, where we drank Guinness and talked about everything from art to soccer to coral reefs until 6:30 p.m., when we’d have dinner at a restaurant nearby. After dinner we all went back to our hotel and collapsed, happy after a fulfilling day that had fed our brains and souls. After each meeting, everyone went home with a task: compiling experimental studies on ecosystem functioning, analyzing global fishing data, or thinking of how to present the data—all to answer Loder’s question: Why is marine biodiversity important? Or, more to her point, why is marine biodiversity important for humans?
We already knew that the ocean produces half of the oxygen in the atmosphere, that living coral reefs and mangroves protect our shores from the destructive effect of storm waves, that the ocean gives us food, and so on and so forth. Those details were not in question. But until then, no one had measured how important marine biodiversity is in providing all these human benefits. Thus our question became: Does more biodiversity equal more benefits? And, conversely, does the loss of biodiversity mean the loss of benefits?
WE AGREED on what we meant by biodiversity, but we needed to come to an agreement on what measure of biodiversity to use. Biodiversity is the variety of life on our planet. Biodiversity includes genetic differences within species (think of domestic dog species—yes, all dogs, from chihuahuas to shepherds, belong to just one species). It can mean differences between species—dogs and cats, for example. And finally, it can mean differences across ecosystems, such as a pine forest compared with a wetland. Biodiversity is not a simple quantifiable concept like temperature or distance, but rather it has several dimensions and can thus be measured in different ways.
The most commonly used measure of biodiversity is species richness, which simply means the number of species in one place. But that measure alone does not tell us how healthy an ecosystem is. For example, think of a pristine coral reef and an overfished coral reef. The pristine reef might have dozens of gray reef sharks, whereas the overfished reef could have just one shark left. In terms of species richness, “reef sharks” count the same in each location. Reef sharks? Check. So we could end up with the same measure of species richness on reefs that are vastly different and far apart on the maturity scale.
Ecologists have developed a better way to measure the variety of life in an ecosystem: the concept of diversity, or ecodiversity. Diversity is a measure of how species are distributed within an ecosystem. It uses the number of individuals or the biomass of a species to represent the relative abundance of that species in its ecosystem. In other words, a diversity assessment considers how evenly or equitably species numbers are distributed in a given place.
To give a couple of examples: A natural history museum—or Noah’s ark—would score at the top of the diversity scale, since those would be the only places where all species are equally represented: two individuals per species, a female and a male. But an ecosystem like that could never work in nature. Imagine New York City with just two doctors, two nurses, two teachers, two taxi drivers, two pizzamakers, two garbage collectors, two canine stylists, and so on and so forth. Definitely not a functional city. In the same way, a functional coral reef will have different abundances for every species of coral, worm, sponge, and fish. The distribution of abundances will depend on the type of ecosystem, the number of species in that ecosystem, the productivity of the habitat, and the maturity of the ecosystem, among many other factors. A general rule is that a more mature ecosystem will contain more species and hence will exhibit greater diversity.
Other measures of biodiversity include the different roles that species play in an ecosystem (predator, habitat creator, or decomposer, for example) and the degree of symmetry of the boundary between ecosystems (for example, the oak forest turning into a pine forest on the mountain slope of Corsica). This complexity of units and scales makes it impossible to assess biodiversity using a single measure. It can also make it confusing for people, including biodiversity experts! But we in our NCEAS working group firmly believed that as long as we were clear about what we were measuring and what our goals were, we could answer the important questions about the value of marine biodiversity.
We were surprised, though, by how little information was available on these aspects of the ocean. We collated published studies on local experiments, long-term regional observations, and global fisheries data. We systematically searched major scientific journals from 1960 to 2005 for marine or estuarine experiments that measured any indicators of biodiversity. For example, three American scientists had conducted an experiment at the Tijuana River National Estuarine Research Reserve, just north of the United States–Mexico border. Their goal was to figure out which had a larger biomass: a marsh with more species or a marsh with fewer. They established plots with zero, one, three, or six plant species in them and observed the plots over three years. Their experiments showed that the plots containing more species accumulated more plant biomass and more nitrogen—a key nutrient. The plots with six species had almost double the plant biomass as the plots with just one species. Furthermore, the plots with more plant biomass had more complex three-dimensional structures, more microhabitats for invertebrates, more food for birds and fish, and so on and so forth. In other words, the more species of plants in the marsh, the more of everything else there was. Experiments elsewhere showed that experimental plots with more biodiversity at all levels (from number of species to genetic diversity to number of ecological functions) were more stable and more resilient, able to withstand perturbations and bounce back afterward. Other experiments tested how biodiversity manifested itself in diets and found that more diverse diets optimized fecundity, growth, survival, and the movement of energy up the food web. In short, the more biodiverse an ecosystem, and the greater the diversity of functions the ecosystem supports, the better and more efficiently it functions.
To test whether these small-scale results scaled up in time and space, we compiled data on coastal and estuarine ecosystems and from other sources. We were able to obtain data from 12 regions in Europe, North America, and Australia, along a gradient of human impact, including areas where biodiversity had been depleted, had collapsed, or had gone extinct, and places where biodiversity had recovered. Comparing places along that gradient showed that coastal and estuarine regions with more biodiversity support better fisheries, and provide a healthier nursery habitat for many species, including commercial fish. In addition, more biodiversity meant that invertebrates such as mussels, oysters, and sponges were able to filter much more water and improve the health of these ecosystems. In contrast, places that had lost much of their biodiversity suffered several times more harmful algal blooms and fish kills, with the resulting beach and shellfish closures—some as long as 35 years. Regions with reduced biodiversity also suffered almost 10 times more species invasions, and significantly greater risk of coastal flooding, because the “natural infrastructure” such as wetlands that are able to retain vast amounts of excess water was gone.
Moving to larger scales, we analyzed global fishing trends, using national fisheries statistics since 1950. Countries report their catches to the Food and Agriculture Organization of the United Nations (FAO), but there is a great deal of variety in the quality of the data. For example, industrial fishing data are more readily available than small-scale artisanal fishing. Typically, countries tend to underreport their catch. Aware of this problem, my friend Daniel Pauly, a renowned professor at the University of British Columbia, led a monumental process to “reconstruct” those catch data. Collaborating with an army of local researchers around the world, Daniel and colleagues were able to obtain data on previously unreported fisheries (small-scale fisheries, for example) and revised the data reported for industrial fisheries. The FAO statistics showed that global marine catches increased steadily since 1950, peaking in 1996 at 86 million metric tons and then slightly declining. But Daniel’s reconstructed catch data disputed that paradigm: The new data showed that the global catch had actually peaked at 130 million metric tons and has been declining more sharply since 1996. We reached “peak fish” 24 years ago.
We looked at how many of those fisheries had collapsed—that is, commercial species whose abundance at sea had been depleted below 10 percent of their original abundance—since 1950. A third of the exploited fish populations had already collapsed as of 2003. As predicted by data at smaller scales, the collapses were much more frequent in ecosystems with fewer species, while the average catches and the speed of species recovery after depletion were both higher in species-rich ecosystems. In other words, the same level of fishing effort would be more likely to degrade a marine ecosystem faster in a species-poor environment than in an environment with more species.
As our work came to a conclusion, the team believed we had done what we were supposed to do. We posed a question—Why is marine biodiversity good for us?—and we tried to answer it using all available information. We mined the scientific literature for ways to make any link between biodiversity and ecosystem benefits and services. We looked for patterns across regions with different species richness and confirmation that the patterns we observed occurred at different levels of biodiversity.
The results were clear. The more biodiversity, the more benefits a marine ecosystem provides for us: better and more resilient fisheries, flood protection, cleaner coastal water, less incidence of disease because of contaminated fish and shellfish, and so on and so forth. Therefore, when human activities reduce biodiversity, they also reduce the ability of the ocean to provide for us. That was something that we thought evident, but we finally had hard evidence to prove it, and to satisfy those who don’t have the benefit of intuition gained by years of experience in the field.
THERE WAS ONE MORE important question to answer: Can we recover ecosystem benefits once they have been depleted? Protecting a pristine place is a way to maintain the benefits that place provides, but what was not so clear was whether we could revive a degraded ecosystem and bring back all the services it once could yield. That would mean the difference between hope and despair.
Independent studies show that no-take marine reserves where fishing is prohibited have a biomass of fish on average six times greater, with 21 percent more species, than unprotected areas nearby. And the fish are, on average, a third larger. In short, protecting marine waters increases biodiversity within their boundaries.
Our analysis also showed that recovering biodiversity inside marine reserves helped to improve the fisheries around them. Around the areas studied, fishers caught four times more fish, on average, for the same amount of effort. Tourism revenue also increased significantly—because divers want to see fish, not empty water, and thus more visitors flock to marine reserves. We concluded that it is still possible to recover lost biodiversity, and that such recovery will likely be followed by increased productivity and more stability, which in turns means better fish catches around reserves and higher non-extractive revenue (tourism) within them.
SO THAT’S ONE STEP: We can bring depleted ecosystems back to healthy biodiversity. But what if we push diversity to the extreme? What happens to vastly transformed ecosystems like the mass-production agricultural fields that feed us and our feedlot animals? Is there any chance of recovering biodiversity there, and is there any value in doing so?
In 1998, an international team of scientists, led by Zhu Youyong of Yunnan Agricultural University in China, set up an ambitious study to answer a simple question: Can diversity in rice varieties protect the crop from diseases? Rice is affected by a fungus that causes blast, a disease also known as rice rotten neck. The fungus kills the tip of the rice plant as it starts to flower, damaging it before it produces the grain. Yunnan Province was an ideal experimental site since it has a cool, wet climate that harbors fungus and fosters blast epidemics. Zhu and his colleagues engaged thousands of Yunnan rice farmers to participate in their experiment.
Sticky rice varieties command higher prices in the market, but they are highly susceptible to blast disease. Nonsticky hybrid rice varieties are less susceptible, so at that time 98 percent of the area’s rice was grown as a monoculture: rows and rows of one or the other of two nonsticky hybrid varieties.
For the experiment, some fields were planted with a monoculture of sticky rice, some with a monoculture of hybrid rice, and some with a mix of the two, following a pattern already used by some farmers to obtain a minimum yield of sticky rice for the local market: one row of sticky rice flanked by two rows of hybrid rice on each side.
The results were very clear: Twenty percent of the sticky rice in the monoculture fields contracted blast disease, but only one percent of the sticky rice plants in the mixed fields were affected. But there is more: Grain production rates of sticky rice in the mixed fields were on average 89 percent greater than those in monoculture. Taking all factors into account, mixed populations produced more total grain per hectare than the monocultures. Another example of the value we gain from biodiversity.
IN SCIENCE, it is not always easy to provide an answer to a question as simple as the one Natasha Loder posed: Why is biodiversity important? It took years to scan the scientific literature and conduct our own analyses before we had a strong, solid response, but we can now answer her question based on the evidence of science. Simply put, the more biodiversity ecosystems have, the more productive, stable, and resilient they are—and the more benefits we obtain from them. Even agriculture benefits from crop diversity.
It would be easy for someone to argue that that’s a no-brainer. Doesn’t every successful long-term investor tell us that we have to diversify our portfolio to increase our returns? But our established agricultural practices of industrial monoculture do not seem to be following that obvious analogy. Be that as it may, investing in biodiversity—that is, preventing further decline and restoring as much as possible—is essential for the future of humanity. Natural ecosystems are both our savings accounts and our life insurance policies. We need to ensure that our natural capital portfolio is well diversified.
Now the question is, How do we restore our natural capital?