Home

Feature: Oceans on the Edge

Feature: Fall of the Magic Kingdom

Feature: Reporter on a Global Beat

Interview: Jan Perchenik - The Ocean as Frontier

Feature: From Sea Soup to Casco Bay

TUAA: Distinguished Service Awards

Newsworthy

Bookshelf

Back Page

Archives

 

Interview: The Ocean as Frontier

Biologist Jan Pechenik on the amazing diversity of marine life

For more than 20 years, Jan Pechenik has hauled the smallest members of the ocean's animal kingdom back to his office in Dana Laboratories. In jars of seawater he has carried home clouds of larval barnacles, mussels, sea squirts, worms, crabs, and parasitic flatworms, to name a few, and he has published research papers on all of them. These days, Pechenik is preoccupied with Crepidula fornicata, better known as the slipper shell snail or, to beachcombers, as mermaid's toenails. As larvae, Crepidula are nearly invisible, like large dust particles suspended in water. But under a microscope's magnifying lens, their swimming transparency is captivating: one can see a tiny beating heart, a thread of intestines, and the whir of tiny "hairs" called cilia that propel their round forms. Hard to believe that these microscopic busybodies will eventually mature and harden into snails that live out their lives attached to rocks, surrounded by mud. Hard to believe that this is the same snail that, through ship ballast water, has invaded the waters off France and severely damaged a once-thriving oyster industry.

Author of Biology of Invertebrates, now in its fourth edition, Pechenik respects the importance, complexity, and richness of marine organisms, especially of invertebrates like the slipper shell snail. Invertebrates, as he reminds his students, far outnumber vertebrates, making up at least 98 percent of all animal species. Through his research as well as his teaching and writing, Pechenik explores the dynamic nature of invertebrate zoology. We are only beginning to learn about the complex lives and interrelationships of these ocean organisms. Below, he talks with editor Laura Ferguson about a necessary awe of the ocean's vast ecosystem.

Do we know a lot more about ocean life than we did fifty years ago?
Sure, but we still don't know everything. Most of the species that live in the ocean have probably not even been described yet. The very deep ocean is in fact the largest but least explored habitat on the planet. There are probably thousands, maybe millions of undescribed species living down there. Some people think the deep sea might be as diverse or more diverse than tropical rain forests. But what is happening in the deep sea, and even in much shallower waters, is essentially invisible to most of us.

So it really is a kind of frontier?
Definitely, and one that is really just beginning to be explored in many ways. For example, a lot of marine animals live sedentary lives attached to rocks, pilings, and ship bottoms. Put a new piling into the water and it becomes encrusted with all sorts of interesting organisms in a few weeks. But if you look at many sedentary invertebrates like sponges or soft corals, you don't see other animals growing on them very often. There aren't many predators that eat them either. Why not? It turns out that many of these invertebrates have very interesting, often unique chemical defenses against predators and against other animals and algae that might otherwise grow on them. In some cases those chemicals are actually inducible, so that animals don't start producing the chemicals unless they are being preyed on, for example. You probably don't expect that kind of sophistication from a coral or a sponge. But you see it in a variety of species from different animal groups. And it turns out that some of these chemicals may well have biomedical advantages for us, as anticancer agents, for example.

One aspect of your research focuses on sea ballast discharge and how it introduces nonindigenous species into new habitats. How serious is bioinvasion?
The problem is certainly growing. More than 240 nonindigenous species have been introduced through ship ballast water transport into San Francisco Bay alone, with estimates of one new successful introduction taking place there every 12 weeks. The consequences are hard to predict, but some have been devastating. In the Black Sea, the $250 million fishing industry has essentially come to a halt, largely because of ballast-mediated invasion by comb jellies from the East Coast of the United States about 20 years ago. The best known example is probably that of the zebra mussel, which was introduced from ship ballast into the Great Lakes about 15 years ago, most likely from the Caspian Sea. These fingernail-size freshwater mussels have spread throughout the Great Lakes and most of the major river systems in the eastern United States, clogging industrial and municipal water intake pipes and driving a lot of other species to, or at least toward, extinction. One species of snail that I study, Crepidula fornicata, was introduced off the coast of France probably by supply ships from England at the end of World War II. This animal has now taken over many of the most productive oyster beds along much of the French coastline. Some of these areas now support thousands of tons of these snails, preventing the oyster beds from being harvested effectively. While apparently harmless in its native waters off New England, the snail is most unwelcome in France. I've been invited to spend a week in France this summer to examine the situation and possibly develop some joint research. But I wouldn't argue that all biological invasions are going to be so disruptive. After all, the common intertidal periwinkle was introduced to the U.S. from Europe over 100 years ago and now we think of it as native.

How does your work relate to the problem in France?
I've spent many years studying the development and metamorphosis of the slipper shell snail. One of the things we're interested in finding out is whether the larvae are being stimulated to metamorphose by the presence of adult oysters. But more generally, I'm interested in understanding why some species have successfully invaded new areas while others have not, even species with widely dispersing larvae that could easily end up traveling in ship ballast. It turns out that some of the stresses larvae are likely to experience during such ballast water transport can reduce their growth and competitive potential as juveniles. Determining which species are most or least sensitive to such stresses might help us explain the patterns of invasion that have been documented so far, and might help us predict which species might successfully invade in the future.

What led you to study invertebrates?
For one thing, the diversity of invertebrate lifestyles and reproductive patterns is just enormous. If you are interested in evolution, and particularly in the evolution of life cycles and reproductive patterns, as I am, then you have to love marine invertebrates. Crepidula fornicata, for example, is a snail that acts more like a clam: the gill that normally is just a gas exchange surface has become modified into a food-collecting organ, just the way it is with clams, so that the snails can feed without having to move. That's true of a great many marine animals; they make their livings sitting down. But how do they disperse? On land, adults typically disperse and offspring typically stay put. But most marine adults travel very little and instead produce free-living dispersive larvae. These larvae can be carried tremendous distances by water currents; in some species, they will actually metamorphose and grow to adulthood on the opposite side of the Atlantic or Pacific Oceans. On the other hand, many species have lost the larval stage from the life cycle. What pressures have selected for that loss? What are the genetic mechanisms underlying that loss? What are the consequences of no longer producing larvae? Are human activities favoring animals with certain reproductive patterns, or selecting against those with other reproductive patterns?

Also, as terrestrial vertebrates, we think it normal for individuals to be separate sexes. But in the ocean, many species, including Crepidula, are sequential hermaphrodites: they start off as males and eventually become females. But there is flexibility in the timing of the change in sex. With Crepidula, for example, if you are a male sitting on a female's shell, you will stay a male for a much longer period of time than if you are with another male. In fact, if you take two males and put them together, the oldest, largest one becomes a female within a few weeks and the other remains a male for months. Other animals are simultaneous hermaphrodites. Barnacles are male and female at the same time. And there are oyster species that change sex every few years. The more you know about the animals the more fascinating they become. In fact, much of what we currently understand about the control of gene expression, mitosis, aging, pattern formation during embryonic development, the biology of fertilization, nerve function, and vision, and even the genetic basis for a predisposition to some major diseases have come from studies of invertebrates.

Why do you call phytoplankton the unsung heroes of the sea?
A large percentage of the air that we breathe is courtesy of phytoplankton. Not only do they increase the amount of oxygen, but they also remove tremendous amounts of carbon dioxide from the atmosphere, something like 2 gigatons of carbon per year. Without them the CO2 concentration in the air would probably be much higher than it is now. Their photosynthetic activities get carbon out of atmospheric circulation for long periods of time, storing it in the ocean waters and sediments for thousands of years. If the phytoplankton population were to decline dramatically, not only would it disrupt food chains, but it could also have a big impact on the ability of the ocean to absorb excess carbon dioxide from the air. Nobody really knows what would happen. Probably there is only one way to do the experiment, and we may all be doing it together right now!

Is there an attitude that the ocean can assimilate anything?
Yes, and because the life of the ocean is largely invisible, we don't immediately see the consequences of our activities. Even so, it is becoming hard to ignore that we are having an impact, that we are dumping more pollutants into the ocean than it can handle, and that we are removing seafood from the ocean faster than it can be replenished. The Worldwatch Institute has published a number of very accessible booklets on these issues over the past few years.

So we are learning it has limits?
That's right. You find DDT in animals living in the Arctic and around Antarctica and in the deepest recesses of the ocean. We hear about the catastrophic effects of major events like oil spills, but pollutants also often have very subtle effects on marine organisms. Very low concentrations of pollutants can affect the mating behavior of animals and damage their embryonic and larval development. Larvae especially are vulnerable: they are typically 10 to 100 times more sensitive to pollutants than are the adults of the same species. And these microscopic larvae are found in the life histories of most marine animals. Corals, clams, snails, sea urchins, worms of various sorts, lobsters, crabs, fishes-representatives from every phylum. That adds an additional element to what I said earlier about the biological problems of the ocean being largely invisible to us. We can conduct experiments on larvae in the laboratory, but we can't see whether larvae are developing normally or not in the field, we can't even monitor how well they're surviving, or even where they're going. But it's those sensitive, microscopic larval stages that will ultimately determine where the adults will live, or whether there will in fact be any adults.

We shouldn't be concerned only about the immediate, visible impact of our activities on marine fishes and mammals. Many of the pollutants that we add to the ocean are water soluble and are taken up rapidly by phytoplankton. Those phytoplankton are eaten by larval and adult stages of many marine invertebrates, and those animals ultimately serve as food sources for other marine animals, including the ones we eat. The fate of large marine animals is linked to what happens lower in the food chain.

And of course, then there is the fisheries issue. Any gains we've seen in seafood availability over the past 10 years have been due almost entirely to aquaculture production. But even there we're running into major problems. Shrimp production, for example, consumes tremendous quantities of clean water and generates a great deal of pollution. In Asia, commercial-scale coastal shrimp farming also involves massive destruction of mangrove communities, which are of course the natural breeding grounds for wild shrimp populations. This robs local people of their food supply and livelihood and reduces biodiversity. And guess what the cultured shrimp are fed? Diets rich in fish meal and fish oils; raising a pound of shrimp consumes about 2-4 pounds of fish, so that shrimp farming actually results in a net loss of protein!

What can biologists do?
Well, biologists can define the problem and tell you what is going wrong and what might be causing it. But fixing it is probably out of our hands, and predicting the consequences of our actions is also not something that is very easy for us to do; the system is just too complex. The key role of biologists is probably to document the extent of the problems as they develop. I hope we're not simply documenting our own demise!

Where do you think the solutions will come from then?
I think that solutions are largely in the realm of economics, and sociology, and politics, and ethics, more so than in the area of biology. Ultimately, the problem, if you really step back and take an honest look, lies in human population growth. More people, more consumption, more waste production. Most of our environmental problems are ultimately caused by the increasing numbers of people on the planet (along with excessive resource consumption by some of us).

So you see these issues all connected to the pressure of human population on resources?
We have to realize that population growth has consequences. We've just crossed the 6 billion mark. For most of the past 2,000 years the human population was much, much lower. The planet didn't see 1 billion people until about 1800, but growth has been explosive since then. We've seen a net gain of nearly 1 billion people just in the past 10 years, and demographers are predicting an addition of about 3 billion more people over the next 50 years. With that growth comes more consumption and more waste generation. It is going to be really interesting to see what happens over the next 20 years or so. Suppose everyone in China-population of 1.2 billion-is driving a car 20 years from now. Can you imagine the environmental impact that would have? For people in China to start eating fish at the rate that fish are consumed in Japan, for example, would require the entire annual world fish harvest. The projections I've read are really remarkable.

Do you remain, despite the growing scale of our environmental problems, an optimist or a pessimist?
A friend of mine who is a biologist just shakes his head and says that humans are a failed species, it is just a question of time. After all, 99 percent of all animal species that have ever lived are now extinct! I would hate to be quite that pessimistic, but certainly we are going to lose a lot of what we have now. Each generation sees what it has more than what it has lost. I'm used to seeing the Meadow Glen Mall on my way to Nahant for seawater and I don't really think much about it. But if you had been living along the banks of the Mystic River a hundred years ago you would be very depressed to see the Meadow Glen Mall there now. As the world becomes more and more like the Meadow Glen Mall and less like the world that we travel to for vacations, I think it will become a lot less satisfying to be here. I think it is not just the number of people the earth's resources can support-that is not the full issue. How many people can the earth support while sustaining the quality of life we'd like to have? Maybe individual actions can make a difference, if enough individuals act. Helping conservation groups buy land, eating lower on the food chain more often than we do now, walking and biking, supporting family planning and public transportation, recycling, all of these things can probably help if enough people sign on. We each have to ask: Are we willing to lead simpler lives so that there's something left for others?

   

 

© 2001 Trustees of Tufts University, all rights reserved.