Passage 1
Are Horseshoe Crabs Really Crabs?
Despite their common name, horseshoe crabs are not really crabs (crustaceans). Atlantic horseshoe crabs (Limulus polyphemus), which swarm U.S. coastlines each summer from Maine to Mexico, have been called "living fossils" because they predate the dinosaurs by more than 200 million years. Their smooth, hard shell (exoskeleton) is shaped like a horseshoe (thus the name). They use their long tails as rudders in the water and to flip themselves if they get overturned on the beach—not as weapons, which is commonly assumed.
Few people realize how important horseshoe crabs are to modern medicine. Because their blue, copper-based blood quickly clots in the presence of bacterial toxins, medical researchers use it to test intravenous drugs, vaccines, and medical devices, ensuring that they are free of bacterial contamination. Every year, many thousands of horseshoe crabs are harvested from their habitats, "bled" of about one-third of their blood, then returned to the beach.
Horseshoe crabs are also important ecologically. Loggerhead sea turtles and more than 20 species of migratory birds rely on the crabs' eggs as an annual boon to their diets.
Atlantic horseshoe crab numbers have been declining since at least the 1990s. Delaware has the largest population of horseshoe crabs in the world, and scientists from NOAA's National Estuarine Research Reserves System are studying the species there. Reasons for the crabs' reduced numbers include habitat loss and high demand as commercial bait. Scientists are currently working to develop artificial bait that may potentially reduce the number of horseshoe crabs taken for bait.
Passage 2
from Delaware's Shorebirds
An incredible and spectacular display of nature's majesty occurs every spring on the Delaware Bay—a unique phenomenon not seen anywhere else in the world. Each spring, hundreds of thousands of shorebirds converge on the shores of the Bay. They've been traveling a long way. Some, like the red knot, travel as many as 5,000 non-stop miles. The farthest-flung red knot populations spend the winter at the southern tip of South America, while other populations winter in Brazil and the Southeastern U.S. Come spring, they're all on their way to the Arctic where they breed during the short Arctic summer. Delaware Bay is the final and most critical rest stop for these migratory specialists.
They're drawn to Delaware Bay by the promise of food; they time their arrival to coincide with the horseshoe crab spawning period. During this time, vast numbers of protein-laden horseshoe crab eggs are just waiting to be gobbled up in a dazzling feeding frenzy on the beach. The horseshoe crab eggs sustain the shorebirds for their remaining 2,000 mile trip to the Arctic. During their brief stay here, shorebirds that arrive emaciated from a long flight from South America can double their body weight!
But today, this amazing natural cycle is being disrupted. The exact causes are complex and under debate. But the bottom line is this: Delaware's shorebirds are in trouble. The numbers are alarming: where nearly 100,000 red knots once made their springtime stopover, only about 25,000 visited in 2009. Other species such as Ruddy Turnstone, Sanderling, and Semipalmated Sandpipers have declined in number as well. Clearly, our natural legacy–unique to Delaware–is in serious jeopardy.
3
Select ALL the correct answers.
Which two statements best synthesize the information from both passages?
Both horseshoe crabs and red knot shorebirds swarm the U.S. coastlines in the summertime.
The declining population of horseshoe crabs is affecting the number of shorebirds seen in Delaware.
Red knot shorebirds and horseshoe crabs are both beneficial for medical research.
Both horseshoe crabs and red knot shorebirds double their body weight when eating to help them survive the long migration.
Horseshoe crabs are ecologically important for the survival of the red knot shorebirds.
The declining population of horseshoe crabs is affecting the number of shorebirds seen in Delaware.
Horseshoe crabs are ecologically important for the survival of the red knot shorebirds.