If you’ve ever been to John F. Kennedy International Airport, you were probably worried about a lot of things: long security lines, delayed flights, grumpy New Yorkers. All are valid concerns. You probably didn’t spend much time worrying about turtles. Little did you know, turtles make their way onto JFK airport’s runways every year, sometimes delaying flights for hours (Reardon, 2011). The real trouble with terrapins, however, isn’t on JFK’s runways. It’s with their nests. Or really, the lack thereof. Researchers have been studying these terrapin populations for over a decade at Jamaica Bay Wildlife Refuge, a nature preserve just 5 km from JFK in New York. In that time, they’ve observed a 50% decrease in the number of diamondback terrapin nests laid each year (Rubenstein, 2014).
What’s happening in Jamaica Bay to cause this decline? There are two parts to this problem. First, the whole terrapin population is declining (Reardon, 2011). Fewer females means fewer nests. The second problem is that females are laying fewer nests per year. Female terrapins usually next two to three times a year, but research suggests they may be nesting fewer times per year at Jamaica Bay Wildlife Refuge (Rubenstein, 2014). In both cases, it likely all comes down to one thing: food.
The health of Jamaica Bay, the body of water neighboring JFK airport and surrounding Jamaica Bay Wildlife Refuge, has long been declining. Four different New York City waste water treatments plants feed into Jamaica Bay, releasing tremendous quantities of nutrients such as nitrogen into the water (Benotti et al., 2007). Excess nutrients in the water have caused algae to proliferate, preventing other vegetation from getting the light and nutrients they need. Due to this nutrient pollution, as well as sea level rise, Jamaica Bay’s wetlands are declining at an alarming rate (Rubenstein, 2014). The amount of wetland vegetation in the bay declined by almost 40% from 1974 through 2002 (Hartig et al., 2002). This loss of wetland habitat has led to declines in terrapin’s main food sources: clams and mussels. So instead of eating protein-rich clams and mussels, terrapins are stuck eating algae (Rubenstein, 2014).
What’s so bad about eating algae? Algae doesn’t provide the same amount of proteins and other nutrients as clams and mussels. Proteins play a vital role in the production of energy and can have a big impact on an animal’s metabolic rate. Metabolic rate is the speed at which chemical reactions, such as the production of energy, occur in the body. All animals require a minimum amount of energy to keep their body functioning and survive. This minimum amount of energy needed, called the basal metabolic rate, is represented by the red line in the figure below. Metabolic rate depends on a number of factors, including temperature. For turtles and other ectotherms, which are animals whose body temperature depends on the external temperature, the minimum amount of energy an animal needs increases with temperature (Randall et al., 2008).
An animal’s metabolic rate can also depend on the amount of food, and therefore energy, available. Any energy not used up by their basal metabolic functions can be used to fuel processes beyond just survival, such as growth and reproduction. The blue line in the figure above represents the maximum amount of energy an animal can use, called their maximum metabolic rate. The distance in between the basal and maximum metabolic rate represents the amount of energy that can be used for extra activities like growth and reproduction and is called the aerobic scope (Randall et al., 2008).
Since Jamaica Bay terrapins are stuck eating more algae and less protein-rich food, their ability to grow and reproduce may be compromised. All or most of the energy they get from their food may need to be used to maintain their basal metabolic rate just to survive. As a result, terrapins may not have the energy to reproduce as often, causing them to reproduce fewer times each year than in the past. If algae doesn’t provide enough energy for terrapins to meet their basal metabolic rate, individuals may not even be able to survive, which would explain the declines in population size that are also being observed.
If we truly want to understand why New York’s terrapins are reproducing less and less each year, further research about their metabolic needs, food availability, and population size is needed. But based on current evidence, large-scale efforts are needed to minimize nutrient pollution and to preserve the remaining wetlands in Jamaica Bay if we hope to protect these terrapin populations.
By Becca Czaja
Benotti MJ, Abbene M, Terracciano SA. 2007. Nitrogen Loading in Jamaica Bay, Long Island, New York: Predevelopment to 2005. USGS. https://pubs.usgs.gov/sir/2007/5051/SIR2007-5051.pdf.
Hartig EK, Gornitz V, Kolker A, Mushacke F, Fallon D. 2002. Anthropogenic and Climate-Change Impacts on Salt Marshes of Jamaica Bay, New York City. Wetlands 22 (1): 71-89.
Randall D, Burggren W, French K (2008) Eckert Animal Physiology: Mechanisms and Adaptations. W.H. Freeman and Company, New York.
Reardon, Sara. “Why JFK’s Runway Has Turtles All the Way Down.” Science. 30 June 2011. Accessed 15 January 2019. http://www.sciencemag.org/news/2011/06/why-jfks-runway-has-turtles-all-way-down.
Rubenstein, D. “A turtle mystery in Jamaica Bay.” Politico. 30 October 2014. Accessed 15 January 2019. https://www.politico.com/states/new-york/city-hall/story/2014/10/a-turtle-mystery-in-jamaica-bay-017034.