Think your parents are tough? Try being a sea turtle
People have some pretty diverse perspectives on raising kids—from the hands-on “helicopter” approach to the hands-off “free-range” style.
In the ocean, the parenting spectrum is even more extreme. Evolution has formed wildly different strategies for plants and animals to create future generations.
The ocean’s helicopter parents are marine mammals, such as orcas and whales. They give birth to one or two calves a year and invest heavily in each one’s survival. Mother orcas give their babies milk and teach them to hunt; the pod provides social connections and protects against predators.
Other animals, such as sea turtles, are hard-core free-range parents—leaving their offspring to fend for themselves from the start.
“Sea turtles may lay a thousand eggs in one breeding season. The hatchling babies that scurry into the ocean have just a week of food in what remains of their yolk sac,” says Kyle Van Houtan, director of science for Monterey Bay Aquarium. “But the mom and dad are never around to teach them what it means to be a turtle. All they have is instinct.”
Without a grown-up around, the hatchlings look elsewhere for role models. “Essentially,” Kyle says, “the ecosystem or the climate is their parent.”
That’s where we come in. People are affecting the earth’s climate by burning fossil fuels, which emit carbon dioxide and other heat-trapping gases. That means our daily decisions, like whether to drive or bike to work, can make a surprising difference in the life of a sea turtle.
Without any parental investment, baby sea turtles are at the mercy of the ocean. That includes the weather: temperatures, wind patterns, ocean currents and precipitation on any given day.
The bigger influence is from climate, which is the cumulative weather over an extended period of time, like a month, season, or longer.
Climate drives the currents that deliver nutrients across the ocean. That’s a big deal for marine life. Changes in the climate can determine whether baby turtles are received into productive, nurturing conditions—or depleted, harsh ones.
“The ocean seems like a stable place to us. But it changes, sometimes in predictable ways,” says Francisco Chavez, biological oceanographer at the Monterey Bay Aquarium Research Institute.
One fairly predictable climate cycle is the El Niño-Southern Oscillation, which happens about every two to seven years. During an El Niño event, Pacific trade winds stop blowing (usually in late December), setting off a chain reaction. Warm, tropical water spreads east toward South America, and the usual weather patterns in some parts of the Pacific reverse. Typically wet regions in Australia and South Asia may experience droughts; drier regions along the coasts of Peru and California may get drenched. El Niño’s sibling, La Niña, comes on El Niño’s heels and has the opposite weather effect. Together, they form the ENSO cycle.
Most of the time, we are not experiencing ENSO conditions. But another climate cycle, called the Pacific Decadal Oscillation (PDO), is always happening. It’s a pattern of alternating warm and cold sea surface temperatures in the Northern Hemisphere. Each phase can persist for decades.
During a positive PDO phase, the west Pacific (off Japan) cools and the east Pacific (off California) gets warmer. During a negative phase, it’s the opposite. Francisco was one of the first scientists to notice the PDO’s dramatic influence on fisheries across the Pacific Ocean. Cooler surface waters supported big sardine populations, while anchovy numbers dropped. Warm phases caused the opposite: more anchovies, fewer sardines.
A few years ago, Kyle noticed a similar ebb and flow in the numbers of adult loggerhead sea turtles. He thought about Francisco’s fisheries research and drew some similarities between sardines and sea turtles.
Both are cold-blooded creatures sensitive to water temperatures. Both share a “free-range” parenting strategy—producing lots of offspring, then letting them fend for themselves, with few making it long enough to have babies of their own.
That gave Kyle an idea.
He found that a cohort of loggerhead turtles born during a postive-PDO year had a larger-than-average population 30 years later. In other words, hatchlings born into certain ocean conditions had a better chance of surviving into adulthood. That suggests loggerhead turtle populations are linked to climate cycles.
In a paper published in May, Kyle showed why. Baby loggerhead turtle survival depends on ocean circulation—specifically the Kuroshio Current, which zips past loggerhead nesting areas in southern Japan.
During negative PDO phases, the Kuroshio Current sweeps the tiny turtles into warm, unproductive waters to the south where there is little food. Making matters worse, because turtles aren’t warm-blooded, being in warmer waters makes them hungrier. In other words, decades of negative PDO conditions can devastate loggerhead populations—simply because they were born at the wrong time.
Positive PDO phases, on the other hand, are good times for these turtles. The powerful Kuroshio Current weakens, allowing hatchlings to swim to cooler, more productive waters at higher latitudes. These lucky turtles have better changes of finding food, getting strong and growing up. A few decades later, there’s a bump in the adult loggerhead population.
The carbon-current connection
The helicopter parents of the ocean world are better able to shelter their young from the dramatic impacts of climatic shifts. Baby orcas, for example, stay in the same pod for their entire adult lives, and family members share prey with one other. Marine mammals’ big brains give them another advantage: smarts. Gray whales, for example, can alter their migration routes to go where the food is most plentiful.
But this isn’t just a story about natural climate cycles in the ocean. By burning fossil fuels like coal and petroleum, humans are also changing the earth’s climate. As we pump extra carbon dioxide into the atmosphere, the planet is warming, and scientists predict more conditions like those that occur during negative-PDO phases. That could spell big trouble for loggerheads.
“Climate change is such a huge issue. It’s hard to know where to begin,” Kyle says. “This work helps us focus on which species need our help the most, right now.”
Francisco is concerned that people continue to drive climate change, some species may be unable to survive through the nutrient-poor phase of these ocean cycles. “The populations that can hang on until it’s good again thrive,” he says. “But it might get to a point where they can’t hold on anymore.”
The good news is, the ocean is resilient. By working together to burn fewer fossil fuels and shift to cleaner energy sources, we can reduce the pace of climate change and ocean acidification—giving vulnerable animals like sea turtles a better chance to survive and thrive.
In a sense, it takes a global village to raise a sea turtle. You can start today, with actions as simple as carpooling and turning off your lights. Learn more about the ocean impacts of rising carbon emissions on the Aquarium’s Climate Action page.