Originally appears in the Winter 2009-2010 issue

Visits to much of North America’s coastline involve splashing in clear ocean waters, strolling along sheltered beaches and indulging in local seafood delicacies. While you are enjoying these offerings, clams slowly burrow downward in the wet sand beneath your toes. Near the mouth of a nearby stream flowing into the estuary a great blue heron methodically hunts. Farther out, by a distant rock, a harbor seal plays. And holding this moment together? Swaying unassumingly, just below the waterline, is eelgrass. A simple gaze at this innocuous plant does little justice to the important role that eelgrass has come to play in estuaries and coastal waters.

Along the coastlines from eastern Canada down to North Carolina, and from British Columbia to California,1 eelgrass plays the critical role of supporting the tremendous weight of a coastal food web. The plant, ranging from only a few centimeters to over two meters tall, is responsible for improving and maintaining water clarity,2 reducing wave energy and slowing water currents,3 providing food for small invertebrates, and creating shelter for juvenile fish species, many of which are commercially important.4

Despite its important roles in coastal ecosystems, eelgrass is in decline throughout its distribution area. This decline is commonly attributed to nutrient and sediment loading5 associated with shoreline development. The following provides background information for teachers and activities that focus on the protective role of eelgrass (Predator Snapshot), the complexities involved in cleaning up polluted watersheds (Clean up the Bay!), the effects of environmental stressors on eelgrass function (Stressful Situation!) and the effects of declining eelgrass populations on fish (Habitat Hopscotch).

Well, what IS eelgrass?

Eelgrass, one of approximately 60 species of aquatic plants known as seagrasses, can be found off the coast of every continent except Antarctica.6 Seagrasses are not true grasses, but marine flowering plants that grow in shallow coastal waters. Except in some shallow intertidal beds, seagrasses are always submerged and do not possess a rigid leaf structure to provide support. However, they are the only group of marine plants with root systems),7 enabling these plants to play a critical role in coastal ecosystem. Zostera marina is the dominant species of seagrass found in the temperate waters off both coasts of North America.

While eelgrass can grow in intertidal waters, it is important to recognize that seagrasses are not salt marsh plants. Plants growing in salt marshes, such as cordgrass (Spartina alterniflora) and salt hay (Spartina patens) are salt-tolerant terrestrial grasses, not aquatic grasses, even though they are partially submerged during high tide. Eelgrass is also not seaweed. Despite occupying the same waters, eelgrass is a marine plant, while seaweeds are not plants but protists, a kingdom of organisms with no tissue specialization and no root system, and that reproduce asexually.8

The importance of eelgrass

Seagrass ecosystems perform a number of ecologically important functions in coastal waters. The root system of eelgrass helps stabilize sediment while anchoring the plant. The leaves and shoots filter particulate matter out of the water column,9 improving water clarity and light transmission, thus increasing their capacity to photosynthesize. Aboveground, seagrass reduces wave energy and slows water currents, allowing suspended material to collect within the seagrass bed.10 The older leaves and poorly rooted plants are often uprooted in storms, creating floating islands of wrack in an estuary. This dead plant material eventually washes up on shore, where it is an important food source for detritivores (organisms that feed on dead material) such as amphipods.

Eelgrass grows in dense patches known as beds or meadows. The physical structure and camouflaging ability of the seagrass canopy protects juvenile fish and invertebrates from predation. Because juvenile fauna are regularly found in eelgrass beds, the beds are often referred to as “nursery habitats.” Commercially important species, including flounder and bay scallops, have all been shown to use eelgrass meadows as critical nursery habitat.11 Eelgrass habitat not only provides shelter, but also creates an important link between other estuarine habitats, such as salt marshes, oyster reefs and mussel beds.

Eelgrass; Cornerstone of the Estuarine Food

In estuaries, as in most ecosystems, the energy from the sun fuels the primary producers, such as eelgrass, algae and phytoplankton. Isopods, small arthropods, feed on eelgrass leaves. In turn, the isopods are preyed on by small fish, which seek shelter in eelgrass beds. These fish are preyed on by larger fish, such as striped bass. Harbor seals also feed on the smaller schooling fish as part of their diet.12 In tropical climates, turtles and manatees graze on seagrass leaves.

Some organisms rely on the physical structure of eelgrass for survival. Mud snails lay their eggs on eelgrass blades to prevent their desiccation,13 and blue mussels settle on eelgrass blades to prevent their desiccation,13 and blue mussels settle on eelgrass leaves in their early stages before settling on the substrate.14 Some juvenile invertebrates, such as lobsters, burrow in the mud beneath eelgrass beds for protection against predation.15 Horseshoe crabs forage in eelgrass beds looking for mollusks and marine worms.16 Even birds utilize eelgrass beds during low tide. Wading birds such as blue herons search eelgrass beds for crabs and fish, while Canada geese graze directly on the leaves.17

The dead leaves and other detritus that collects in the eelgrass root system also contribute greatly to the estuarine food web. Gastropods (e.g., snails), grass shrimp and polychetes (marine worms) all feed upon the detrital material in eelgrass beds, which can exceed the biomass of the living plant material.18 The detritivores (organisms that eat decaying material) help convert nutrients in the plant material back into a form usable by the plants as well as serving as another link in the estuarine food web.

If eelgrass is so important, why is it disappearing?

Eelgrass decline has been documented along both coastlines and is primarily attributed to nutrient and sediment loading.19 Shoreline development, characterized by impermeable ground cover such as asphalt and concrete, reduces an area’s natural ability to absorb rain and runoff, promotes soil erosion, and leads to higher sediment and nutrient loads entering the estuary,20 both of which ultimately impact eelgrass growth. Excess sediment in an estuary clouds the water, increasing turbidity and reducing the amount of light reaching the substrate.

In addition to declines caused by nutrient and sediment additions, eelgrass is subject to direct physical damage from docks, boat moorings and propellers, and dredging. Boat docks reduce light levels, shading out plants and fragmenting eelgrass beds.22 Dredging and dragging of the estuary bottom through moorings, channel widening and harvesting of mussels, uproots plants and reduces water clarity by suspending sediment in the water column.23

Activities

Activity 1: Predator Snapshot

The Predator Snapshot activity focuses on the role of eelgrass in protecting juvenile and small organisms. The purpose of the activity is to compare the camouflaging ability of vegetated and bare sediment. While it requires significant preparation, Predator Snapshot is a useful and interactive way to address the structural role of eelgrass in an estuary.

Grade level: 5–8

Objectives:

  • Compare the protective capability of vegetated and bare sediment
  • Understand the importance of eelgrass as a “nursery” habitat
  • Assess one’s own predatory ability

Materials: two clear or white plastic containers of 15 liters (4 gallons) or more in volume; green yarn or pipe cleaners, sand or fine sediment, fish cutouts made from foam, monofilament line, metal sinkers, blindfolds.

Preparation:

  1. Cover the bottom of the containers with an inch or so of sand or sediment and then fill the rest of the way with water.
  2. Set one (or half) container aside – this will be the bare sediment model.  ‘plant’ the other container by burying the ends of the pipe cleaners or yarn in the sediment until the container is covered with eelgrass plants approximately 1 inch apart.
  3. Place the same number of foam cut-outs of fish in both tanks at varying heights — surface, mid-water column and substrate —by tying different lengths of monofilament (fishing line) to the fish and weighing them down with metal sinkers. To explore the concept of clamoufflage within an eelgrass bed, vary the color of the fish so that students can determine which are the easiest/hardest to spot.

Procedure:

  1. Blindfold participants and line them up around the vegetated containers. Explain in this activity, they will play the role of an aviary estuary predator, such as a blue heron. On your command, they are to remove their blindfolds and study the scene in front of them until you give the cue to cover their eyes again. (If blindfolds are not available, participants can cover their eyes with their hands.) During this time, their assignment is to silently count all the animals they can see. Their viewing time will be only three to five seconds. If the group is large and there are not enough containers or space for everyone to go at once, have the participants view in shifts. However, explain that animal counts must be kept to oneself until the very end.
  1. Once the participants have counted fish in a vegetated container, lead them to a bare container and have them do the same thing.
  1. After all of the participants have seen both “snapshots,” allow individuals to share how many animals they were able to see in each container. Which one was easier to spot prey in? Which colors were easier to see? After participants have discussed their findings, take them back to the containers for longer viewing. Discuss how this activity reflects real life. Eelgrass beds are critical habitat for juvenile fish and invertebrate species because they provide protective camouflage, helping to ensure healthy future populations. What would be the effects on higher trophic levels if there were no eelgrass beds?

Activity 2: Clean up the Bay

This activity focuses on the complexities of cleaning up polluted waters. The activity connects well with Stressful Situation!, which focuses on the effects of water quality on seagrass populations.

Grade level: 5–8

Objectives:

  • Distinguish between effective and ineffective clean-up techniques
  • Understand how individual actions add up on a watershed-wide scale
  • Identify ways to mitigate individual contributions to watershed pollution

Materials: For each group of six students, one clear or white container of approximately four liters (one gallon) volume, filled half way with water; one pitcher of water, approximately 1 liter (one quart); six film canisters; six “pollutants” from readily available household materials (e.g., food coloring for nutrient additions, coffee grounds for sediment, vegetable oil for motor oil); four to six tools for “cleaning” the water (e.g., strainers, slotted spoons, tongs)

Procedure:

  1. Divide the participants into groups of approximately six. Give each group a container of clean water and a set of film canisters filled with the pollutants and labeled accordingly. Set aside the second containers of clean water for later.
  2. Depending on the age of the students, brainstorm potential sources of the six pollutants. Then allow each student to add a pollutant to the water until all canisters are empty.
  3. When all of the pollutants have been discharged into the container, provide each group an assortment of tools for cleaning the water. Have them pick the item they think will be most useful and justify their reasoning (e.g., tongs for large material, strainer for smaller sediment). Continue having the groups choose the next best tool until they have exhausted their options.
  4. Have the students look at their containers and consider whether they successfully cleaned their water. Provide the groups with the second one-liter container of clean water for comparison. What were they able to remove and what weren’t they? (While much of the particulate matter will likely have been removed, pollutants dissolved in the water will remain). What tools were most useful and why?
  5. Take a minute to brainstorm with the participants how the remaining pollutants might be removed. Offer the students the clean water as a way of treating the polluted water. Does this help? In real life, is adding more clean water a feasible solution for improving water quality? Have students brainstorm the consequences of increasing the quantity of water in a system (flooding). While adding more water isn’t a good option, what would have the same effect? If less of the pollutants were added to a watershed in the first place, so much wouldn’t accumulate. Brainstorm ways to reduce pollution additions. Have each person think of an example specific to the pollutant he or she added to the clean water earlier in the activity. Which actions would be easy to accomplish and which would not?

Activity 3: Stressful Situation!

This activity emphasizes the impact of stressors on eelgrass productivity. The term “stressor” is used to describe any factor (cloudy water, excess nutrients) that inhibits the functional ability of eelgrass (photosynthesis, root growth, leaf growth). The stressors can be as broad or specific as the instructor needs to emphasize particular inputs of the system.

Objectives:

  • Observe the effects of environmental stressors on overall eelgrass function
  • Monitor the functional ability of stressed plants
  • Identify possible mitigation efforts to improve eelgrass function

Materials: four cones or other objects to mark boundaries

Preparation: In a gymnasium or large outdoor area, mark two parallel lines 8–10 meters (25–30 feet) apart and long enough for all participants to line up along them.

Procedure:

  1. Have participants stand along one of the lines. One member of the group will be an environmental stressor, such as turbid water, and the rest will be eelgrass plants. The stressor begins by standing in the area between the two lines, facing the other participants. On the designated signal, the eelgrass will run to the opposite line. It is important to explain that the movement back and forth does not represent eelgrass uprooting itself and running along the floor of an estuary. The motion is illustrating the productivity of different processes within a plant (photosynthesis, root growth, leaf growth). As the eelgrass passes from one side to another, the role of the environmental stressor is to tag as many individuals as possible. Once plants cross the line, they are off limits for the stressor.
  1. When all of the participants are standing on the opposite line, ask for a show of hands from those who were affected (tagged) by the stressor. Plants that were affected have a lower functional ability than the healthy plants. To represent this, the plants affected by the stressor must cross the playing field hopping on one leg in the second round.
  1. Once all of the plants have crossed for a second time, ask the participants how many healthy plants were affected by the stressor. These individuals will lose the use of one leg in the next round. Then ask how many stressed plants were again affected by the stressor. These doubly stressed plants will be reduced to crawling in the next round. If in subsequent rounds the highly stressed (crawling) eelgrasses get tagged by the stressor, they will be considered dead and must sit out the remainder of the activity. An alternative is for dead eelgrass individuals to become additional stressors in the system.
  1. After several rounds, discuss the implications of the different stress levels. How did the stressor affect healthy plants? (Slowed them down slightly/reduced ability to carry out normal functions). How did the stressor affect the already stressed plants? (Severely reduced movement/function of plants). What might these stressors be? (Cloudy water from sediment or algal blooms caused by nutrient loading). How could we reduce their effect? (Reduce their input into the system: plant vegetative buffers to reduce sediment, apply less fertilizer, better sanitation systems).

Activity 4: Habitat Hopscotch

Habitat Hopscotch is an active game that highlights fragmentation of eelgrass habitat in the Great Bay Estuary. It was adapted from Migration Headache24 and Wetlands Hopscotch.25

Objectives:

  • Understand the implication of habitat fragmentation on higher trophic levels
  • Learn potential causes of habitat loss in the Great Bay Estuary
  • Identify possible solutions and mitigation efforts for habitat loss

Materials:10–15 carpet squares or other non-slip placemats to represent eelgrass beds, 8–10 “fate cards” (see examples below) in a bag or other container

Possible Fate Cards:

  • Eliot builds a golf course on the waterfront – remove 1 square
  • Newington develops a water park next to the river – remove 1 square
  • Wagon Hill Park purchases abutting land for more trails – remove no squares
  • Newmarket installs a new sewage treatment facility – remove 1 square
  • Summer houses build on Nanny Island – remove 2 squares
  • Newington power plant shut down – remove no squares
  • Restoration effort replants grass – add 1 square
  • Students urge conservation commission to re-vegetate park below Oyster River dam – remove no squares
  • Clear cutting for new housing development – remove 1 square

Procedure:

  1. Start the activity by arranging the “eelgrass patches” (carpet squares) into a hopscotch-like formation. Explain to the participants that they have been transformed into small fish within the Great Bay Estuary. Their mission is to travel from one end of the estuary to the other without getting eaten by larger predators. To do this, the fish must remain within eelgrass habitat at all times. Start by letting each fish hop easily from eelgrass patch to patch until they reach the end of the estuary.
  1. Have the one of the participants pick a fate card from the bag and read it aloud. Apply the fate to the eelgrass and have the fish travel through the estuary again. Fish who are not able to make it from one end of the estuary to the other are eliminated from the round. At the end of each round, determine by a show of hands how many fish survived. For future or graphical analysis, the instructor can record the number of eelgrass patches and surviving fish.
  1. Play through several rounds with the fate cards until the students can no longer travel the entire estuary or understand the implications of habitat fragmentation. Afterwards, discuss with the participants what potential actions could be taken to reduce or restore eelgrass habitat.

Notes

  1. F.T. Short, T.J.B. Carruthers, W. Dennison and M. Waycott, “Global Seagrass Distribution and Diversity: A Bioregional Model,” Journal of Experimental Marine Biology and Ecology 350 (2007) pp. 3-20.
  2. F.T. Short and C.A. Short, “The Seagrass Filter: Purification of Estuarine and Coastal Waters,” in V.C. Kennedy (ed.), The Estuary as a Filter, Academic Press, 1984, pp. 395-413.
  3. M.S. Fonseca, J.S. Fisher, J.C. Zieman and G.W. Thayer, “Influence of the Seagrass Zostera marina L. on Current Flow,” Estuarine, Coastal and Shelf Science 15 (1982), pp. 351-364; and
  4. E.M. Koch, “Beyond Light: Physical, Geological, and Geochemical Parameters as Possible Submersed Aquatic Vegetation Habitat Requirements,” Estuaries 24 (2001), pp. 1-17.
  5. K.L. Heck, K.W. Able, C.T. Roman and M.P. Fahay, “Composition, Abundance, Biomass, and Production of Macrofauna in a New England Estuary: Comparisons Among Eelgrass Meadows and Other Nursery Habitats,” Estuaries 18 (1995), pp. 379-389.
  6. F.T. Short and S. Wyllie-Echeverria, “Natural and Human-induced Disturbance of Seagrasses,” Environmental Conservation 23 (1996), pp. 17-27.
  7. C. den Hartog, The Sea-Grasses of the World, Amsterdam: North-Holland Publication Co., 1970; and E.P. Green and F.T. Short (eds.), World Atlas of Seagrasses, University of California Press, 2003.
  8. Short et al., 2007.
  9. Fish and Wildlife Research Institute, “Seagrass Versus Seaweed,” Florida Fish and Wildlife Conservation Commission, 2008.
  10. Short and Short, 1984.
  11. Fonseca et al., 1982; and Koch, 2001.
  12. Heck et al., 1995.
  13. Northeast Fisheries Science Center, “Seal FAQs,” Woods Hole, MA: Woods Hole Science Aquarium, 2007, p.2.
  14. D.A. Coulombe, The Seaside Naturalist, Simon and Schuster, 1984, p. 246.
  15. Heck et al. 1995; and R.E. Grizzle, F.T. Short, C.R. Newell, H. Hoven and L. Kindblom, “Hydrodynamically Induced Synchronous Waving of Seagrasses: ‘Monami’ and its Possible Effects on Larval Mussel Settlement,” Journal of Experimental Marine Biology and Ecology 206 (1996), pp. 165-177.
  16. F.T. Short, K. Matso, H.M. Hoven, J. Whitten, D.M. Burdick and C.A. Short, “Lobster Use of Eelgrass Habitat in the Piscataqua River on the New Hampshire/Maine border, USA,” Estuaries 24 (2001), pp. 277-284.
  17. NYS DOS. “New York State Significant Coastal Fish and Wildlife Habitat Narrative.” New York State Department of State Division of Coastal Resources; 2002, p. 4.
  18. D.O. Rivers and F.T. Short, “Effect of Grazing Canada Geese Branta canadensis on an Intertidal Zostera marina Meadow,” Marine Ecology Progress Series 333 (2007): 271-279.
  19. S.M. Adams and J.W. Angelovic, “Assimilation of Detritus and its Associated Bacteria by Three Species of Estuarine Animals, Chesapeake Science 11 (1970), pp. 249-254.
  20. Short and Wyllie-Echeverria, 1996.
  21. V. Lee and S. Olsen, “Eutrophication and Management of Initiatives for the Control of Nutrient Inputs to Rhode Island Coastal Lagoons,” Estuaries 8 (1985), pp. 191-202.
  22. 21. A. Deegan, A. Wright, S.G. Ayvanian, J.T. Finn, H. Golden, R.R. Merson and J. Harrison, “Nitrogen Loading Alters Seagrass Ecosystem Structure and Support of Higher Tropic Levels,” Aquatic Conservation: Marine and Freshwater Ecosystems 12 (2002), pp. 193-212.
  23. D.M. Burdick and F.T. Short, “The Effects of Boat Docks on Eelgrass Beds in Coastal Waters of Massachusetts,” Environmental Management 23 (1999), pp. 231-240.
  24. H.A. Neckles, F.T. Short, S. Baker and B.S. Kopp, “Disturbance of Eelgrass Zostera marina by Commercial Mussel Mytilus edulis Harvesting in Maine: Dragging Impacts and Habitat Recovery” Marine Ecology Progress Series 285 (2005), pp. 57-73.
  25. Project WILD Aquatic, “Ecological Knowledge: Wildlife Populations,” in Project WILD Aquatic: K-12 Curriculum and Activity Guide, Council for Environmental Education, 2001, pp. 2-18.
  26. K. Shutsky, S. Kaufman and S. Signell, “Watersheds: Where the River Meets the Sea,” in The ABCs of Ecology: An Educators Guide to Learning Outside, Ecology Education, Inc., 2006, pp. 197-204.

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Nora Beem is the outreach coordinator for tin mountain conservation center in Albany, New Hampshire.  Michael Dufilho teaches environmental education in Olympic National Park, outside Port Angeles, Washington. Dr. Frederick Short is the director of SeagrassNet, a worldwide seagrass monitoring program and is actively involved in seagrass research, conservation, protection and education at the University of New Hampshire.

Research and outreach associated with this article was created at the University of New Hampshire’s Jackson Estuarine Laboratory. It is contribution 488 from the Laboratory towards published literature.