Week 6:marine plants, light and color

Week 6: Marine plants/ Light and color

Time to get out there and explore some plants! In  the last section we learned about a lot of plant-like algae. Now it is time for the real plants: sea grasses and mangroves in particular.

1.) Take another look at chapter 3 of the Seaside Naturalist, this time focusing on the plants.

If you do not have access to seagrass, please visit the following sites to get an idea of what they are like:

Smithsonian Seagrass Underwater Webcam

2.) Take a trip to the coast to an area where you can find some sea grasses. Get into the water with your snorkeling gear (or buy or make an underwater viewer ) and make some close observations of these plants:

  • How closely are the plants spaced?
  • Are they evenly distributed or are there patches of thick growth mixed with thinner or bare patches?
  • Are there other plants or seaweeds growing amongst the seagrass beds or are they largely a monoculture?
  • Do they look healthy?
  • Is anything growing attached to the sea grasses? If so, then what?
  • What fishes or other organisms are you finding amongst the grasses?
  • What substrate are they growing in (sandy, clay, rocky, limestone)?
  • What is the average water depth and temperature?
  • record your observations in your notebook

3.) Collect some specimens of sea grasses. Be sure to collect as much of the plant as you can, including the parts below the substrate. Bring it to your work area for observation.

  • Lay your specimen out neatly and sketch it in your notebook. Be sure to make note of the details of the plant, such as  rhizomes, root length, distance between shoots, number of leaves, presence/shape of sheathes, and any flowering parts if present.
  • Use these details to make an identification of your sea grass. Label your sketch with the Genus and species.

4.) See if you can find some piles of washed-up dead sea grasses on the beach. Look in and under the piles to see what creatures might be washed up or hiding there. Don’t overlook tiny organisms that decompose the piles (such as amphipods and snails). Collect a sample of these creatures in a vial of alcohol to identify under the microscope at a later date. Make sure you label your sample with the date and place you collected it.


You can get a good idea of what mangroves are like, and their importance, by visiting the following sites:

YouTube video: Last Stand

Smithsonian Mangal CayVirtual Tour

Scientific American: Animals of the disappearing mangroves(be sure to look at the slide show)

If you do not have access to mangroves, use the pictures in your text to sketch the three types of mangroves in your notebook and label the pnematophores, prop roots, and propagules. beneath your sketch write a descriptive paragraph  explaining the function of each part, and the importance of mangroves in general.

If you do have access to mangroves, it is time to get out and explore!!!

5.) Walk, swim, or paddle into a mangrove swamp. Note the following:

  • What species are you seeing? How can you tell?
  • Can you spot prop roots, pneumatophores, and propagules?
  • Examine leaves  for salt (black) and petioles for salt extruding pores (white).
  • Take a leaf or two home to examine under the microscope. Can you spot the stomata? Compare to a leaf of another tree. Any differences?
  • make a list of all of the types of creatures you see in the mangroves, and where you see them (on the branches, on the roots, at the water line, submerged,  attached or free-swimming, etc) . Try to identify them as best you can, but we will be looking more closely at these organisms at a later date, so if you can’t identify them, that is ok.
  • Sketch your mangroves in your notebook. Label the parts.

Light and color

6.) Use your research skills (and the handy links in the sidebar) to answer the following questions (record them in your notebook):

  • Why is the ocean blue? What about the sky?
  • What causes the ocean to appear different colors (turquoise, greenish, reddish, brown)?
  • What are the meanings of the terms euphotic, disphotic, and aphotic zones and where in the ocean are they found? Check back in your notebook to the diagram from the first week, if you wish.
  • What determines the depth of the euphotic zone?
  • What types of organisms would you expect to find in each zone?

7.) Read here about refraction, do this flashlight demonstration experiment, try this rising coin trick , and then test your knowledge with the following fun activity!!!!

  • Make 6 water balloons filled with fresh water and perhaps a few lead fishing weights or marbles or smooth rocks (you want your balloon to sink).
  • Grab some darts, a sharpened stick, a diving knife, or other spear-like, throwable objects. Promise your mom you won’t stab yourself.
  • Go to the ocean. Find a shallow, calm spot with a smooth bottom.
  • Sink a balloon in the shallow water, a foot or so deep.
  • Stand back a bit and throw your projectile, aiming at the balloon, and try to pop it. Any luck?
  • Now try again with the rest of the balloons at various angles (various distances and directions away from you). Are you able to hit any? In which direction are your errors? Is there any trick to make it easier or harder?
  • Make a sketch of your activity, and write down your results and conclusions in your notebook.

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