Be an Ocean Biodiversity Detective!

Part of Hall of Ocean Life.

Milstein Family Hall of Ocean Life Educator's Guide: Activity

Be an Ocean Biodiversity Detective!

The majority of organisms in the ocean are tiny invertebrates, protists, and algae. Although the ocean is vast in size, living space for these small organisms is limited to coastal areas and to surface waters where light penetrates—areas where food is plentiful and where there are surfaces on which to fasten and grow. Barnacles and bryozoa, for example, survive by attaching themselves to something larger, and then filter food from the water as it washes over them. Some organisms will find homes on larger moving animals, such as horseshoe crabs and whales. Still others may attach themselves to rocks, the pylons of a dock, or on seaweed.

Have you ever noticed the "necklace" of marine remnants left along the seashore at low tide? With careful observation this assortment of shells and algae, like jewels on a necklace, can reveal a wealth of tiny marine creatures.

In this activity students will collect and closely observe specimens that have washed ashore to recognize different kinds of small ocean organisms. Some organisms will leave parts of their bodies behind, such as shells, while others may leave behind clues such as holes.

What you need:

  • a visit to a sandy beach
  • bag or container for collecting specimens
  • magnifying glass
  • seashore guide - [Recommended: Seashore Life: A Guide to Animals and Plants Along the Beach. Golden Field Guide Series. New York: St. Martin's Press, 2002.]

What you do:

  1. Visit the seashore with your class at low tide for the best selection of washed up marine algae and invertebrate remains. Make a small collection of specimens to observe more closely in the classroom. Students should note the locations of their specimens. Specimens can include eel grass, seaweed, reeds, shells, driftwood, and sand dollars. Look for specimens that appear to have been used by other animals—these will be the most interesting specimens. Don't look for just the pristine and pretty objects. (Be careful not to uproot anything alive!)
  2. In the classroom: Now the detective work begins. Instruct students to closely examine their specimens and identify the primary organism—the original and usually largest organism on which other organisms may have attached. Make observations about the specimens' texture, shape, design, size, color, and patterns. Be sure students look at their specimens from different perspectives—inside and out, top and bottom.
  3. Is the specimen whole or part of a larger organism? Use a seashore guidebook to try to identify the organisms. 
    1. "How long, roughly, has" the specimen been on shore? Is the specimen sharp or does is have round edges? (Broken edges that are now rounded may mean that it has been in the water for a long time.)
  4. Next, ask students to look for clues that reveal what may have happened to the specimen. Where was it found? If it is a broken shell, might an animal have broken it? (A bird could have dropped it against the rocks.) If perfectly round holes are evident, could these have been bored by an animal?)
  5. Have students study the worksheet to recognize the clues left behind by different organisms. Students may use the seashore guide or other resources to help identify the additional organisms they discover. The variety of organisms they find represents biodiversity. The number of each different kind of organism represents abundance.
  6. Ask students to calculate the biodiversity and abundance found in the total sample. 
    1. Is it possible to figure out a sequence of events from the evidence on the specimen? What organisms may have attached first? Which may have come later? What evidence supports this?
  7. Ask students to consider the body designs of the different organisms they have identified. How does the structure of these organisms support their survival?


The June 2002 article in Natural History magazine, "Hitchin' a Ride" contains vivid illustrations of the many organisms that "piggyback" on the horseshoe crab.

Grant, Dave. "Hitchin' a Ride." Natural History, June 2002.

Source: Amy O'Donnell, AMNH 

Copyright © 2003 American Museum of Natural History. All rights reserved.