Playing Lotto in the Sea

Jellyfish short circuit the traditional oceanic food web eating zooplankton, fish larvae, and fish eggs. From Boero 2013.

When I was in grad school, my advisor took a sabbatical and then a few leaves of absence to work at the U.N. Food and Agricultural Organization, or FAO, in Rome. I visited often and I fell in love with the country, it’s food, and energy, and left a small piece of my heart there, where it’s remained for the last 19 years. When my husband Keith told me he had a business trip that would take him to Rome this month, I decided I should go along, and see how my heart was doing.

I justified the trip by wrangling an interview with one of the most well-known jellyfish scientists in Italy, Fernando Boero. During the first months of my jellyfish research, I ran across a paper Boero wrote called, “Gelatinous plankton: irregularities rule the world (sometimes),” which made chuckle. Turns out Boero has a penchant for provoking titles (and he’s not above stealing from Frank Zappa–but that’s another story). Some recent headlines include: The study of species in an era of biodiversity: A tale of stupidity and Time is an affliction: Why ecology cannot be as predictive as physics and why it needs time series.

With a spiky white beard and short cropped hair, Boero (“Call me Nando,” he says) looks like a Portuguese fisherman, but his manner is all Italian. Nando’s speech peppered liberally with, “So c’mon” hand raised in the air to emphasize the validity of his opinion. And Nando has lots of opinions. Opinion number 1: Mathematics is horrible. Any model you can create with equations,  you can do better with words or a picture. There’s a corollary: If you can’t say it in words or with a picture, it’s worthless.

I am just the slightest bit offended, since I was, in fact, a math major in college. And I did, in fact, work on equations for my Ph.D. And I do, in fact, recognize the beauty and elegance of equations and their ability to summarize some kinds of complexity better than words ever could. Nando quickly brushes aside my arguments and I let them rest there on the side to see what else he has to say.

Nando explains that the ecology of the ocean is organized by a set of pulses. In the spring, rains or melting snow wash nutrients into the water. Spring winds drive upwelling that pulls nutrient rich waters from the deep, much like tilling the soil. As spring progresses, waters warm and days lengthen, adding solar energy to the water. The fertile sea warmed and lit by the sun creates ideal conditions for ocean plants, phytoplankton, to blossom. This event is called the spring bloom, and it’s a fixture of coastlines and oceanographic textbooks worldwide.

Of particular relevance to me as I sit typing this blog in an Italian airport cafe staring at a mosaic of zucchini green and tomato red pizza slices sparkling with olive oil:  when there’s food there’s usually someone to eat it. So soon after the spring bloom in the ocean, the animal grazers appear. Shrimplike is often how I describe them, but that’s just a lazy shorthand. The menagerie of zooplankton spans nine phyla and includes skinny clear worms, bright orange baby fish, alien-looking larval crabs and sea stars, and a kaleidoscope of of others.

Following the growth of the zooplankton, the fish come. And that’s really what most people care about. Fisheries have been the cash cow of ocean ecology for millenia.

These three pulses–phytoplankton, zooplankton, fish–are so characteristic of our oceans, that scientists have come to understand the succession as regular as the spring rains, the summer heat, and the leaves falling in autumn. Entire scientific programs are funded and conducted to measure the extent and concentration of the spring bloom, to monitor the zooplankton, and most importantly, to document the fish catch.

But understanding these three pulses should be just the start, says Nando. The really interesting stuff is what happens when those pulses don’t occur, or don’t occur when they are supposed to. What happens when the rains come late in the spring? What happens if the water stays cool a few weeks longer?

Even if the phytoplankton bloom isn’t right on schedule, an adult fish that has plenty of fat reserves is still able to spawn just like it always has. But if rains or temperature delay the spring phytoplankton bloom, the zooplankton population won’t have matured in time for its baby fish to get enough to eat, and they won’t survive.

Suppose there’s another species of fish, one that has always been present, but hasn’t been a dominant species. Suppose that species spawns just a bit later in the spring so that, for once, it’s aligned with the phytoplankton bloom and the zooplankton that follow it. This year, when its babies are looking for a meal, they’ve got it made.

Nando calls it a lottery. “There is a prize–the energy the phytoplankton harvested from the sun–and the winners are those who are able use it.”

In the scientific literature, the idea that the oceanic food web has an inherent element of risk has a name: the match-mismatch hypothesis. When the timing matches up for fish food and fish, the fish win the lottery. When the timing slips, or when something supporting the phytoplankton–light, nutrients, temperature–goes missing, there’s a mismatch.

But remember, all this is based on the model (you can say it with words!) of the three timed pulses that make a food chain: phytoplankton, zooplankton, fish. How do jellies fit into this picture?

Jellies have a complicated life cycle that involves a medusa and a polyp stage. They aren’t directly tied to the three pulses and so they aren’t always in the picture. But when they are, jellies short circuit the system. Gelatinous salps, which eat phytoplankton, shorten the food chain to phytoplankton, salps. Typical jellyfish, like moon jellies and Pelagia, eat zooplankton, and they shorten the food chain to phytoplankton, zooplankton, jellies. Either way, food gets diverted from the fish.

And there’s more. When jellies are present, they don’t just divert the energy from fish, they cut the fish populations off at the, um, fins. Jellies eat fish eggs and larval fish, making it tough for fish populations to replenish themselves.

When jellyfish appear episodically, as has been the pattern for the last several hundred years as far as we can tell, the short circuit doesn’t have a lasting effect. A single year class of fish might be smaller as a result of a jellyfish bloom, but if the population is healthy, the fish, which live for multiple years, won’t suffer greatly from the occasional influx of jellies. In fact, they just might benefit. Like the latest upstart in Silicon Valley, a bloom of jellyfish timed correctly could give an edge to a species of fish that usually doesn’t dominate. Jellyfish could act the disruptive technology that leads to a more diverse system.

But if jellies become the norm, as we’ve been seeing in coastal places and particularly in the Mediterranean lately, then the short circuit becomes permanent, and that’s worrisome. The fish never regain a (sorry!) finhold and the ecosystem does not have a chance to recover. The food chain is in a chronic short circuit. Pithy scientists have called this process “fishing down the food web” and the result “the jellyfish joyride” and they see a future ocean full of the little fish and jellies that can make a living off zooplankton.

Fishing down marine food webs
Fishing down marine food webs from Pauly at al. 1998

While Nando acknowledges this model as reasonable (you can after all draw a picture of it), he thinks that it stops short. What happens after you have an ocean full of little fish and jellies? Nando thinks that’s when you start to see the things that love eating the jellies, things like leatherback  sea turtles, and sunfish, or Mola mola, that look like giant swimming Easter Island heads.

Despite that facts that they are the heaviest fish in the world–reaching two and a half tons–and that they can make up as much as 80% of the swordfish bycatch, Mola biology is not really well understood. No one knows how many there are, how fast they swim, how they mate, and whether or not their numbers are going up or down. But a recent study suggests that shark overfishing coupled with increases in jellyfish abundances could lead to more molas.

Leatherback sea turtles are more charismatic than sunfish, but their biology is nearly as mysterious. Like molas they can reach massive sizes on a diet of jellyfish. They are the largest of all sea turtles with a length of 8 feet and weighing as much as a ton. No one really knows where they go after those cute little babies scurry off into the sea, although new satellite information is starting to provide answers. In the last two weeks, four massive leatherbacks have been found dead tangled in fishing gear off the coast of Scotland, something long-time fishermen found shocking because the last leatherback seen in Scotland was in 2009. Scientists speculate the animals might have been following larger than average swarms of jellyfish near the coast.

So Nando developed a new model of the ocean, which he summarized elegantly in the picture below–no equations needed. After the disruptive action of our present jelly-filled world, here are the winners of our future ocean’s lottery: car-sized fish and reptiles.

Figure 10, FAO Studies and Reviews No. 92
A future sea where sunfish and leatherback sea turtles dominate. From Boero, 2013.



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