GRADE LEVEL: 5-8

TOPIC/SUBJECT MATTER: Life Science/Environmental Science

TIME ALLOTMENT: 1-2 45-minute class periods

OVERVIEW:

This lesson uses video segments from the NATURE film “Crash: A Tale of Two Species” to explore the interrelationship between the horseshoe crab and a small migratory bird called the red knot. Both species are in decline, and the red knot’s future, in particular, depends on the horseshoe crab making a comeback in the waters of the Delaware Bay.

Students will first be introduced to the horseshoe crab via a video segment, learning that the species’ longevity (350 million years) makes the horseshoe crab a “living fossil,” an anomaly in terms of the Earth’s species. They will view several other video segments to explore the interconnectedness between the horseshoe crab and the red knot, following the videos with a discussion of the reasons for the decline of each species. Students will fill out an exit ticket to assess their comprehension of these concepts. An optional additional video segment can be used to explore how humans have come to depend on horseshoe crabs as well (their blood, which evolved to have primitive antibacterial properties, is used to test intravenous drugs for contamination).

As a culminating activity, students will use an interactive online map to research endangered species in the region of the United States where they live. They will discuss the environmental changes that have led to the species’ decline (often of human origin) and will discuss the strategies being employed to prevent their extinction.

MEDIA RESOURCES

Video

NATURE: Crash: A Tale of Two Species (selected segments):

Clip 1: “The Living Fossil”

The horseshoe crab has survived for 350 million years.

Clip 2: “Horseshoe Crabs and Red Knots”

Horseshoe crabs are an essential source of nutrition for migrating birds.

Clip 3: “Protecting the Horseshoe Crab”

Measures have been undertaken to protect the horseshoe crab.

Clip 4: “Horseshoe Crabs and Humans”

The horseshoe crab has immense value to humans for its uses in medical technology.

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Sierra Club Endangered Species Map

This interactive map provides information on key endangered species, including efforts currently being undertaken to protect them, in different regions of the United States.

Standards:

National Science Education Standards

LIFE SCIENCE: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of

• Diversity and adaptations of organisms
  • Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.

o        Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.

As a result of their activities in grades 9-12, all students should develop understanding of:

• The Interdependence of Organisms
  • Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.
  • Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms.
  • Human beings live within the world’s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected.

SCIENCE IN PERSONAL AND SOCIAL PERSPECTIVES: Content Standard F

As a result of activities in grades 5-8, all students should develop understanding of

• Populations, Resources, and Environments
• When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.
• Causes of environmental degradation and resource depletion vary from region to region and from country to country.

Materials

For each student:

• Endangered Relationships Exit Ticket (PDF) (RTF)

For each group of 3-4 students:

• One computer with broadband internet access

For the class:

• One computer for the teacher with a digital projection system

Objectives

Students will be able to:

• Describe characteristics of the horseshoe crab;
• Specify how “living fossils” like the horseshoe crab differ from most other species;
• Understand that over 99% of all species that have ever existed on earth are extinct;
• Name specific factors that can lead to species endangerment and extinction;
• List several strategies that can be undertaken by humans to protect endangered species;
• Provide at least one example of species interconnectedness: how the population decline of one species adversely affects another species.

Prep for Teachers

Prior to teaching this lesson, you will need to:

Preview all of the video segments and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Print and cut out a copy of the “Endangered Relationships Exit Ticket” for each student.

Next: Proceed to Activites

Excerpts from the NATURE episode “CRASH: A Tale of Two Species”

Downloadable QuickTime versions of the video segments:
(Note: To download a video, right click on the video title and click “Save Link As…’ or “Save Target As…”. On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)

Clip 1: “The Living Fossil”

The horseshoe crab has survived for 350 million years.

Clip 2: “Horseshoe Crabs and Redknots”

Horseshoe crabs are an essential source of nutrition for migrating birds.

Clip 3: Protecting the Horseshoe crab

Measures have been undertaken to protect the horseshoe crab.

Clip 4: Horseshoe Crabs and Humans

The horseshoe crab has immense value to humans for its uses in medical technology.

The horseshoe crab is at the center of a contentious debate, and one that plays the world over. How do we find the balance between man and nature?

In the Delaware Bay, the clash over horseshoe crabs has embroiled experts, agencies and people in a heated debate that pits the survival of the red knot against the livelihood of fisherman and the U.S. pharmaceutical industry.

And, in order to find a solution, The Audubon Society, the Atlantic States Marine Fisheries Commission, the New Jersey Department of Environmental Protection, the U.S. Fish and Wildlife Service, conservationists and long-time bay watermen are all looking for one thing, an answer to how many horseshoe crabs there are – and how many there need to be to maintain the ecological balance of the bay if the red knot is to have any hope of survival.

Little is known about the status of the horseshoe crab population. Because their population has only been studied recently, there is limited data which makes it difficult to assess its status. What is known is that prior to 1998, millions of horseshoe crabs were taken from the Delaware Bay in an unregulated fishery. But now, attention is being paid.

Based on recent survey data, the Delaware Bay population appears stable. Dr. Dave R. Smith, Aquatic Ecology Lab, USGS believes evidence from recent assessments and monitoring data indicate that the horseshoe crab population in the Delaware Bay region is experiencing positive population growth. Recent surveys have shown significant increases in the numbers of juveniles and adult horseshoe crabs. These encouraging signs provide hope for the horseshoe crab and shorebird connection in Delaware Bay.

Dr. Smith believes these gains are most probably in response to direct action taken by the fisheries commission because of declining migratory shorebird populations. In 2000, the Atlantic States Marine Fisheries Commission (ASMFC) established state-by-state quotas in all Atlantic states for crabs harvested for bait, limiting the number of horseshoe crabs that could be harvested. And, in 2006, the ASMFC further reduced the number of horseshoe crabs that could be caught in Delaware and New Jersey to 150,000 per year and added additional protection in Maryland and Virginia to increase horseshoe crab abundance in and around the Delaware Bay.

Another crucial step was the establishment of a no-harvest zone (the Carl Shuster Reserve) in the ocean off the mouth of the Delaware Bay. The aim of the no-harvest zone is to protect older juvenile and newly mature female horseshoe crabs from being harvested, allowing them to reach sexual maturity and begin reproducing. Dr. Smith believes that the current management program, which allows only male horseshoe crabs to be caught and taken, will allow for a growth in the population of horseshoe crabs in the bay. Recent monitoring data shows that the number of spawning males has continued to increase significantly in the bay, even with the male-only harvest restrictions in place.

Monitoring programs are in place that will detect important declines in male to female ratios if fisheries managers decide to continue with the current management strategy.

But, according to Dr. Smith, it is important to understand that the harvesting of horseshoe crabs is not the only thing that is keeping their population from growing. Whether the horseshoe crab can ever return in their former numbers is uncertain. They are being threatened by other factors – consequences of climate change and habitat loss loom large on the horizon.

Censusing horseshoe crabs is an imprecise science, and interpretation of survey results may vary. Dr. Larry Niles, Chief Biologist, Conserve Wildlife Foundation, acknowledges the important efforts made by the ASMFC in the past ten years and the possibility that the horseshoe crab population may be increasing. However, Dr Niles believes this improvement, if not a temporary up tick in numbers, is not matched by other surveys done on the Delaware Bay shore where shorebirds are feeding.

Over the six year history of the spawning survey, Niles states there has been no improvement in the number of spawning females. More importantly, surveys of horseshoe crab eggs in New Jersey and Delaware, the food on which the red knots depend, have also shown no sign of improvement in population numbers. In 2007, New Jersey counts of the number of horseshoe crab eggs were the lowest in the history of the survey.

Shorebird biologists found a corresponding 30 percent decline in red knot numbers in 2007 compared to two years ago. Dr. Niles believes it is vital that there are no more losses to the red knot population associated with inadequate availability of horseshoe crab eggs on the Delaware Bay and will continue to argue for further harvest restrictions to assure increases in breeding female horseshoe crabs and their eggs so vital to the red knot.

And yet, it still may be too late for the red knot. Published population models of the red knot indicated that the bird will be at or near extinction in 2010 – just two years from now. Since horseshoe crabs take 10 years to reach sexual maturity, even the restrictions in place now may not be enough to increase this vital food supply for the red knots and ensure their survival. 

But, it is not only the survival of the red knot that is at stake. Like the proverbial canary in the coal mine, the red knots’ decline and potential extinction is a warning sign of larger consequences and danger to come. If steps are not taken to protect our unique ecosystems and wildlife, they may disappear forever.