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Biodiversity: More than we know, less than it was

By Stuart Pimm

The 24 hours of a bioblitz goes by quickly. Everyone wants to know the final total–it stood at 800 by 12.30 p.m., but the numbers will increase as the data sheets are processed. Whatever the final number, it will beg two obvious questions.

How many species are there?

How many species should there have been?

Biscayne Bioblitz 2010.jpg

One can ask these questions of any area–Biscayne National Park, for example, or for all of the world’s oceans. Just how much do we know? And how fast are we learning about what’s there, compared to how fast we are destroying it?

So, the closing ceremonies over, I took the relative calm after the sampling ended and before scientists packed up their gear to talk to three dynamic scientists.

I asked the first question of Dr. Nancy Knowlton, of the Smithsonian Institution, and member of National Geographic’s Committee for Research and Exploration.


Photo of Nancy Knowlton by Stuart L. Pimm

“Most marine diversity is in coral reefs,” she told me. “Perhaps a third of all marine species live in coral reefs. That’s an amazing statistic, when you consider that if you squashed all the reefs together in one place, they would only be the size of Texas or France.

“If we are going to protect the diversity of the oceans, we have to protect the diversity of coral reefs.

“The numbers could be as high as ten million species, but we really don’t know.

“In one recent study, of an area of six square meters of reef, there were almost as many species of crabs as in all of the continent of Europe.

“There’s a huge amount of diversity–and most of it has no name at all.”

Nancy told me about her soon-to-be-published book–Citizens of the Sea. “Its about the Census of Marine Life project–a ten-year effort trying to figure out how many species do live in the ocean.”


Photo of Sylvia Earle by Stuart L. Pimm

I turned then to Dr. Sylvia Earle, a National Geographic Explorer in Residence. I knew that Sylvia had been coming to Florida since she was a child. “What has happened to Florida’s reefs since then,” I asked.

“Putting it simply, they’ve been devastated. There’s the loss of the big fish, the little fish, the corals, the seagrass beds, the mangroves…The habitats have been depleted, modified in dramatic ways,” she said.

“But having said that, what we see here is an example of the ocean’s resilience–and plenty of reason for hope. Those few areas that have truly been protected–and parts of Biscayne Bay are–do have greater diversity and abundance than places elsewhere. The fish there tend to be larger than in surrounding areas.

“Again, there is hope if we take care of what remains, there can be a recovery. It can be a lot better than what it is today.”

I knew that Nancy has recently been on a National Geographic-supported expedition to Palmyra Atoll. “What was it like to be there,” I asked.

“These reefs are in the middle of nowhere,” Nancy told me. “And they have essentially no people living there. The reefs are spectacular–lots of living coral, well over 50 percent and sometimes 100 percent living coral cover.

“Everything that is swimming around is your size–or larger. If you take all the fish and weigh up the fish flesh then 80 percent of the weight is top predators–sharks, groupers, things like that. “

I ambushed my third interviewee just as she came out of the water after swimming around in what she described as a muddy seagrass bed. Clare Fieseler is a graduate student at Duke University’s Marine Lab.


Photo of Clare Fieseler by John Bruno

Clare doesn’t yet have a National Geographic connection: but she was waiting anxiously to hear whether she would get the Young Explorers Grant that she had submitted.

If successful, the grant will enable her to address the question of what happens when fishers remove those top predators that Nancy and Sylvia discussed. Clare’s particular interest is parrotfish.

Clare Fieseler -diving-photo.jpg

Photo of Clare Fieseler by John Bruno

“Parrotfish are key parts of the reef ecosystem. They graze the macroalgae (seaweeds)–that otherwise would grow on the corals. Without parrotfish there, these plants overgrow the corals and take up space on the reef. One then goes from a coral-dominated system to an algal dominated one.”


Photo of parrotfish by Clare Fieseler

In short, the “green slime” takes over. (My apologies to the wonderful macroalgae group who came to the bioblitz–and who showed me the variety of species they found.)

“So why are the parrotfish disappearing,” I asked Clare.

“Snappers and groupers are traditionally the most popular fish because they taste so good. Now that we’ve taken most of those, fishers are going after the parrotfish.”

In short, like a house of cards, taking one out often destroys the structure of natural communities and often in ways that causes further loss of species. Biodiversity is not just a count–it has function too.

Stuart Pimm.jpg

Professor Stuart L. Pimm is a conservation biologist at Duke University, North Carolina. A former member of the National Geographic Committee for Research and Exploration, Pimm is the author of dozens of books and research papers, including the book “The World According to Pimm: A Scientist Audits the Earth.”


 Earlier blog posts by Stuart Pimm>>