The secret to turtle hibernation: Butt-breathing

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Turtles can’t head south for the winter, so they hibernate in rivers, lakes and ponds.

By Jacqueline Litzgus, Laurentian University

To breathe or not to breathe, that is the question.

What would happen if you were submerged in a pond where the water temperature hovered just above freezing and the surface was capped by a lid of ice for 100 days?

Well, obviously you’d die.

And that’s because you’re not as cool as a turtle. And by cool I don’t just mean amazing, I mean literally cool, as in cold. Plus, you can’t breathe through your butt.

But turtles can, which is just one of the many reasons that turtles are truly awesome.

Cold weather slow down

As an ectotherm — an animal that relies on an external source of heat — a turtle’s body temperature tracks that of its environment. If the pond water is 1℃, so is the turtle’s body.

But turtles have lungs and they breathe air. So, how is it possible for them to survive in a frigid pond with a lid of ice that prevents them from coming up for air? The answer lies in the relationship between body temperature and metabolism.

A cold turtle in cold water has a slow metabolism. The colder it gets, the slower its metabolism, which translates into lower energy and oxygen demands.

When turtles hibernate, they rely on stored energy and uptake oxygen from the pond water by moving it across body surfaces that are flush with blood vessels. In this way, they can get enough oxygen to support their minimal needs without using their lungs. Turtles have one area that is especially well vascularized — their butts.

See, I wasn’t kidding, turtles really can breathe through their butts. (The technical term is cloacal respiration.)

Not frozen, just cold

We are not turtles. We are endotherms — expensive metabolic heat furnaces — that need to constantly fuel our bodies with food to generate body heat and maintain a constant temperature to stay alive and well.

When it’s cold out, we pile on clothes to trap metabolic heat and stay warm. We could never pick up enough oxygen across our vascularized surfaces, other than our lungs, to supply the high demand of our metabolic furnaces.

Turtles will bask in the sun to warm up and ease their crampy muscles.
(Patrick Moldowan), Author provided

For humans, a change in body temperature is generally a sign of illness, that something is wrong. When a turtle’s body temperature changes, it’s simply because the environment has become warmer or colder.

But even ectotherms have their limits. With very few exceptions (e.g., box turtles), adult turtles cannot survive freezing temperatures; they cannot survive having ice crystals in their bodies. This is why freshwater turtles hibernate in water, where their body temperatures remain relatively stable and will not go below freezing.

Water acts as a temperature buffer; it has a high specific heat, which means it takes a lot of energy to change water temperature. Pond water temperatures remain quite stable over the winter and an ectotherm sitting in that water will have a similarly stable body temperature. Air, on the other hand, has a low specific heat so its temperature fluctuates, and gets too cold for turtle survival.

Crampy muscles

An ice-covered pond presents two problems for turtles: they can’t surface to take a breath, and little new oxygen gets into the water. On top of that, there are other critters in the pond consuming the oxygen that was produced by aquatic plants during the summer.

Over the winter, as the oxygen is used up, the pond becomes hypoxic (low oxygen content) or anoxic (depleted of oxygen). Some turtles can handle water with low oxygen content — others cannot.

Snapping turtles and painted turtles tolerate this stressful situation by switching their metabolism to one that doesn’t require oxygen. This ability is amazing, but can be dangerous, even lethal, if it goes on for too long, because acids build up in their tissues as a result of this metabolic switch.

But how long is “too long”? Both snapping turtles and painted turtles can survive forced submergence at cold water temperatures in the lab for well over 100 days. Painted turtles are the kings of anoxia-tolerance. They mobilize calcium from their shells to neutralize the acid, in much the same way we take calcium-containing antacids for heartburn.

In the spring, when anaerobic turtles emerge from hibernation, they are basically one big muscle cramp. It’s like when you go for a hard run — your body switches to anaerobic metabolism, lactic acid builds up and you get a cramp. The turtles are desperate to bask in the sun to increase their body temperature, to fire up their metabolism and eliminate these acidic by-products.

And it’s hard to move when they’re that crampy, making them vulnerable to predators and other hazards. Spring emergence can be a dangerous time for these lethargic turtles.

Cold weather turtle tracking

Field biologists tend to do their research during the spring and summer, when animals are most active. But in Ontario, where the winters are long, many turtle species are inactive for half of their lives.

Understanding what they do and need during winter is essential to their conservation and habitat protection, especially given that two-thirds of turtle species are at risk of extinction.

X marks the spot. Former graduate student Bill Greaves tracks turtles during a cold Ontario winter.
Author provided

My research group has monitored several species of freshwater turtles during their hibernation. We attach tiny devices to the turtles’ shells that measure temperature and allow us to follow them under the ice.

We’ve found that all species choose to hibernate in wetland locations that hover just above freezing, that they move around under the ice, hibernate in groups and return to the same places winter after winter.

Despite all this work, we still know so little about this part of turtles’ lives.

So, I do what any committed biologist would do: I send my students out to do field research at -25℃. We are not restricted to fair-weather biology here.

The ConversationBesides, there is unparalleled beauty in a Canadian winter landscape, especially when you envision all of those awesome turtles beneath the ice, breathing through their butts.

Jacqueline Litzgus, Professor, Department of Biology, Laurentian University

This article was originally published on The Conversation. Read the original article.

Mangroves protect coastlines, store carbon – and are expanding with climate change

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Mangroves in the Florida Everglades.
Alan Sandercock, CC BY

Samantha Chapman, Villanova University

With the help of technology, humans can traverse virtually every part of our planet’s surface. But animals and plants are less mobile. Most species can only live in zones where temperature and rain fall within specific ranges.

As regions become warmer due to climate change, plants and animals in those areas will either move to more appropriate climates or be replaced by newcomers who are well-suited to the new conditions. These changes are already occurring. For example, many plants, animals and birds in the Northern Hemisphere have shifted their ranges northward.

My research team studies mangroves – salt-tolerant trees with branches that intertwine like dense jungle gyms. Mangroves line the world’s coastlines and prefer warm temperatures, so they have traditionally been restricted to subtropical and tropical environments. But they have many features that have enabled them to survive major climate shifts in the past. Now, in a harbinger of climate change, mangroves are expanding from tropical zones into temperate areas. Scientists are finding them at higher and higher latitudes in North America, South America, Asia, Africa, Australia and Latin America.

Working with other ecologists in the shadow of the huge launch complex at Florida’s Kennedy Space Center, we have found that mangroves have increased in abundance by 70 percent in just seven years over an area of 220 square miles (567 square kilometers). This is a dramatic change in the plant community along this stretch of the Atlantic coast. Unlike many other impacts of climate change, we expect these shifting ranges to produce some benefits, including increased carbon storage and storm surge protection.

The world’s mangrove forests in 2000.
Giri et al., Journal of Biogeography (2008)., CC BY-SA

Traveling by water

Plants have less ability to move than animals, but some – particularly mangroves – can disperse via water over thousands of miles. Mangroves release reproductive structures called propagules, similar to seeds, which can produce new plants. They float and are distributed by ocean currents and, sometimes, big storms. As mangrove propagules drift north along the Atlantic coast, they are reaching areas where winter freeze events that could kill them are becoming less common due to climate change. Similar movements are occurring in other locations around the world.

In the Gulf of Mexico and Florida, mangroves are increasingly found in areas recently dominated by salt marshes, which typically occur in cooler zones. Using satellite images and land-based field studies in our ongoing study of mangroves, we can see this spread of mangroves occurring faster than we could have expected based on climate data alone.

Though these shifts also likely happened in the past due to hurricanes and freeze events, the recent changes in mangrove range are still dramatic. One study from Florida shows that mangroves from northern populations may be reproducing earlier than normal and producing bigger propagules, which could help them take over salt marshes.

Mangrove propagules drifting near Australia’s Great Barrier Reef.
Brian Gratwicke, CC BY

Stabilizing coastlines

In a recent modeling effort, we examined how mangroves protect NASA facilities at the Kennedy Space Center. We found that a 2-meter-wide strip of mangroves along the shore can reduce wave height by 90 percent. In contrast, it takes 20 meters of salt marsh habitat to reduce waves by the same amount. Other studies have found that mangrove forests helped reduce shoreline damage during the catastrophic 2004 Indian Ocean tsunami and Tropical Storm Wilma in Belize in 2005.

Mangroves around the world have been severely reduced by human activities, particularly clearance for aquaculture. Scientists estimate that at least 35 percent of global mangrove habitat was lost between 1980 and 2000. One recent estimate suggests that mangrove deforestation rates in recent decades have been three to five times faster than other forests around the globe.

All types of coastal wetlands help to prevent millions of dollars in damage from flooding and save hundreds of hours of labor to repair storm damage. Mangrove restoration efforts are ongoing in many parts of the world, including the Tampa Bay estuary and southern China, but some projects have been major failures. To succeed, these initiatives need to consider mangrove habitat needs, particularly hydrology.

Though mangroves may protect coastlines even more effectively than salt marshes, it is important to note that marsh plants provide important habitats for numerous species of birds and fish. We don’t yet know how these animals will fare as mangroves replace marshes, nor do we yet understand other downsides of plant range shifts due to climate change.

Mangroves provide essential habitat and coastline protection but are under threat.

Storing carbon in flooded soils

Continued mangrove expansion could increase carbon storage along coastlines. Mangroves have an enormous capacity for sucking up carbon dioxide and other greenhouse gases and trapping them in flooded soils for millennia. They are among the most carbon-rich tropical forests and can store twice as much carbon on a per-area basis as salt marshes. During normal growth, mangroves rapidly convert carbon dioxide into biomass. The saturated soils in which they grow contain low levels of oxygen, which bacteria and fungi need as fuel to break down dead plant matter. Instead, this dead material is stored in the soil.

We estimated in one study that mangrove carbon storage at the Kennedy Space Center increased by 25 percent in only seven years as mangrove forests spread. We concluded that if mangrove expansion continued unchecked by freezes into other southeastern U.S. wetlands, wetland carbon storage could result in the uptake of 26 million metric tons of carbon by 2080. This is equivalent to just over 95 million metric tons of carbon dioxide, which is about 28 percent of Florida’s total greenhouse gas emissions from human activities in 2010.

Preserving coastal mangroves improves climate resilience in several ways. First, if the carbon stored in these soils were released as carbon dioxide and methane, this would likely cause an increase in climatic warming. Second, the same processes that store carbon in wetland soils also allow these wetlands to accrete sediment and keep pace with rising sea levels.

Can mangroves keep delivering these services?

Plants and animals perform many ecosystem services for humans, from pollinating crops to filtering drinking water supplies. As species are shifted around the globe, it is critical to understand whether these services will lessen or increase, and how we can maximize them in a less stable future.

The ConversationMangroves are providing extremely valuable services and may become even more important as they expand toward the poles. But according to one recent study, many mangrove ecosystems are not building enough new elevation to keep pace with sea level rise. In a new project, my research group is analyzing how variable climate and mangrove invasion will alter the coastal protection capacity of Florida wetland ecosystems. With a better understanding of this process, we can develop strategies for protecting and restoring these valuable resources.

Samantha Chapman, Associate Professor of Biology, Villanova University

This article was originally published on The Conversation. Read the original article.