Undergraduate Program in Plant Biology, University of Maryland



  1. Aquatic Biomes
    1. similar to terrestrial biomes, types of plants and animals present reflect the temperature, depth, available nutrients, and salinity of the environment.
    2. examples: tropical marine, temperate marine, freshwater
  2. Chesapeake Bay
    1. Estuary: body of water open to the sea but with a large input of fresh water from the land.
    2. The Chesapeake Bay facts:
      1. it is the largest estuary in the United States, and also the most productive.
      2. it receives about half its water volume from an enormous 64,000 square mile watershed.
      3. like most estuaries it is an enormously productive ecosystem from abundant:
        1. Light- shallow depth of water
        2. Water- replenishment from watershed
        3. Nutrients- washed off land in over 50 rivers and brought in on tides as salts in sea water
          1. feeds primary producers in the ecosystem:
            1. ) algae which are the primary producers in all aquatic ecosystems whether fresh, brackish or marine.
            2. ) The SAVs - the submerged aquatic vegetation or the bay grasses that carpet the shallows of the Bay.
            3. ) marshes grasses - the grasses growing between low and high tide.
    1. All the aquatic plants we will look at are either algae or angiosperms.
    2. Phytoplankton
      1. microscopic unicellular algae
      2. form the base of the food chain in aquatic ecosystems
      3. exist by the hundreds or thousands in every drop of Bay water - one reason why the Bay water is so murky.
      4. Two major groups of algae in the Bay- vary with time of yearDiatom algae
        1. Diatoms
          1. Instead of cell walls, each cell is surrounded by a 2-part silicon (glass) case that fits like a petri dish.
          2. flourish in colder water, so they are the dominant algae in the Bay in the spring and fall - and the favorite food of oysters.
          3. When the cells die they decompose but the glass shells are resistant to decay, so they drift to the bottom. Over time they may form deposits called diatomaceous earth, and these can be found in Calvert County and southern Anne Arundel County.
        2. Dinoflagellates

        3. Dinoflagellate algae
          1. become dominant in the summer when the water warms
          2. Cause red tide - a bloom (sudden population explosion) of dinoflagellates. (a mahogony tide, a modest bloom, is more prevalent in the Bay)
          3. responsible for massive fish kills along the coast.
            1. ) Pfiesteria, called "the cell from hell, a predatory alga first seen in the estuaries of North Carolina that has caused the death of tens of thousands of fish there.
            2. ) secrete a toxin that stuns the fish, then they attach the fish, which form lesions:
            3. ) In the Chesapeake Pfiesteria has been found in low concentrations in portions of the Pocomoke River on the Eastern Shore and the Patuxent River here along the Western Shore.
            4. )In the summer of '97 Pfiesteria and fish with lesions were found in the Pocomoke; currently DNR is monitoring water quality there and has discouraged fishing or swimming in the Pocomoke.
          4. Bioluminescent when agitated. Has anyone seen the waters of the Bay light up on a summer night?
    3. SAVs -- The bay grasses - (overview here)
      1. Until recently the bay grasses were like an underwater carpet along the shallow waters of the bay
      2. Also called hydrophytes spend lives underwater
      3. hydrophytes have evolved some interesting anatomical and morphological adaptations.
        1. SAVs evolved from terrestrial plants that re-invaded the sea
        2. Holes or spaces (called lacunae -Latin for space) in the tissue of the seagrass.
          1. Up to 60% of leaf volume is air space
          2. allow for gas exchange throughout plant
            1. ) O2 exchanged from production in photosynthesis to places needed for respiration
            2. ) CO2 exchanged from production in respiration to places needed for photosynthesis
          3. Aid in Flotation- upright leaves get more light than sunken leaves
        3. Location of Chloroplasts
          1. in seagrasses the chloroplasts are in the epidermis, not in mesophyll- intercept more light
        4. Adaptation to constant water movement
          1. leaves are thin, strap-like and supple.
          2. allows them to withstand tidal currents and wave action.
        5. thick tangled mat of rhizomes that keep them attached to the soft bottom- not roots
          1. an adaptation to soft substrate bottom of the Bay - mostly a soft muddy substrate -
          2. allow fast vegetative growth- primary mode of reproduction
        6. Adaptation to water pollination
          1. Pollination creates special problems in an aquatic environment.
          2. Their pollen are released in gelatinous strands that are carried by water currents.
      4. Ecological Functions
        1. Rhizomes stabilize bottom
        2. Leaves baffle wave energy (less destructive to shoreline)
        3. Promote sedimentation (silt falls out), thereby improving water quality
        4. Provide habitat/nursery/shelter for hundreds of organisms, including: sea horses, grass shrimp, small fishes.
        5. Grass beds are a major source of detritus, and the estuarine food chain, unlike terrestrial food chains, is based on detritus - few plants eaten directly.
        6. Grass beds are a direct food source for some animals - especially diving ducks
    4. Marsh Grasses of the Chesapeake
      1. marshes that line the edges of the Chesapeake-domain of the marsh grasses
        1. Salt marshes are closest to the sea- high amount of salt water
        2. Brackish marshes are further up Bay where there is a mix of salt water and fresh water
        3. Fresh water marshes are even further up the bay where mixing with salt water is minimal
      2. tidal marshes only exist between the high and low tide lines, form an important transitional zone between the grass beds and upland vegetation.
      3. marsh plants inhabit a difficult terrain, and so have evolved some interesting adaptations to survive.
        1. Difficulties of living in the marsh:
          1. Water salty enough to kill most other forms of vegetation
          2. A soft muddy bottom that doesn't offer much support
          3. A water-logged oxgen poor substrate
          4. The ebb and flow of tidal currents twice a day
      4. Plants that have adapted to these conditions have this narrow edge of land to themselves.
        1. Spartinas: dominant in the lower ends of the Bay
          1. Spartina alterniflora- saltmarsh cord grass in the low marsh
          2. Spartina patens, or saltmeadow hay is in the high marsh- different from S. alterniflora in being shorter and wiry and forms "cowlicks"
        2. adaptations in marsh grasses
          1. ) Xerophytic adaptations- adaptation to low water stress- salt water is very drying to tissue
            1. ) Two possible ways of adapting to salt
              1. ) get rid of the salt that comes in,
                1. ) One method the Spartinas use is to remove the salt via salt glands.
                2. ) a group of cells sunken in the epidermis that collect and pump salt out onto the surface of the plant. Then rain and tides wash the salt off the plant.
              2. ) deal with it once it gets into the cells.
                1. Other marsh plants deal with the potentially harmful salt in their cells by taking up water to dilute the salt content.
                2. -see this in plants that have succulent leaves and stems
          2. Anchoring
            1. ) Because marsh soils are soft and muddy, and because there is mechanical stress from the tidal currents, the Spartinas are doubly anchored.
            2. ) grow by thick rhizomes just under the soil surface. But the Spartinas also produce 2 types of roots along the rhizome: thin water-absorbing roots, and also deep stout roots that lack root hairs so they don't function in water uptake, but act to anchor the plants.
          3. Like the bay grasses, they are also rooted in anaerobic soils,
            1. ) And so, the problem is how to get O2 to the roots and rhizomes.
            2. ) In response to that stress these plants have solved the problem as the bay grasses have done - they have lacunae in the roots and rhizomes that allow the O2 produced in the leaves to diffuse down to respiring cells in roots and rhizomes.
      5. Farther up the Bay where the water goes from salt to brackish the vegetation changes, and the Spartinas are replaced by wild rice and cattails
      6. Ecological Roles of Marsh Plants
        1. Their massive rhizome surface and deep roots stabilize the soft sediments and reduce erosion.
        2. They improve water quality by:
          1. Trapping sediment, which helps water quality
          2. Absorbing excess nutrients and pollutants- before they enter the bay
          3. Provide food for the food chain. The marsh plants and SAV are seldom eaten directly - but rather as are eaten as detritus (plant matter after it has dies-it becomes covered by bacteria which are then eaten). Remember that estuarine ecosystems have a detrital food chain - where everyone eats detritus or eats what eats detritus.
          4. The marshes are also habitat for many animals:
            1. ) oysters and mussels attached to the rhizomes
            2. ) periwinkles - small snails that move up and down the Spartina stems with the rise and fall of the tide
            3. ) large wading birds like egrets and herons
            4. ) mammals like nutria and muskrat
  1. The high productivity of the algae and the SAVs and the marshes have fueled an amazing wealth of life in the Chesapeake - the bay that H.L. Mencken called "a giant protein factory."
  2. But much of that productivity has been declining in the past years, and much of that decline is due to the degradation or destruction of these plant communities (see map of sea grass beds). (stress factors)
    1. succulent blue crabs that, since the decline of oysters, are our most economically valuable species. Our Bay accounts for half of the nation's blue crab harvest - we harvest million lbs. a year.
    2. But they also seemed to be declining and our response used to be to control harvest and limit the numbers of commercial crabbing licenses.
    3. Today we realize how important the grass beds are to the crabs. Grass beds are the habitat of choice for juvenile crabs - they are found there at densities 30 times greater than in non-vegetated areas.
      1. And it's into the grass beds that the molting crabs go to molt. They are encased in a hard shell and the only way they can grow is to shed the old shell and then enlarge. But for 24 hours they are tender and vulnerable until their new, larger shell hardens, so they hide in the grass beds. Watermen know this because they collect the tasty soft shell crabs there.
      2. Realizing the importance of grass beds to the crabs, the management of crabs to ensure their survival includes not only restrictions on size or numbers of crabs, but also improving the grass beds to maintain the stock of crabs.
      3. Not only are the grass beds critical habitat for many organisms but they also improve water quality by causing sediment to settle out.
    4. the water is clouded with sediment - no light for photosynthetic organisms, and silt clogging the gills of clams and oysters.
  3. Since the 1960s there has been a great die-off of the grasses and today most of the beds that used to line the Bay are gone, primarily due to excess nutrients and sediment that enter the Bay.
    1. And ironically, the ecosystem that actively removed these 2 pollutants - the marshes - are also disappearing. Over half of the marshes that historically edged the Bay are now gone.
    2. The process begin in the 1930s when the marshes were ditched and drained:
      1. This was done by the Army Corps of Engineers as a way to increase agricultural land.
      2. Today the destruction continues, but we - not the farmers - are the culprits: Everyone wants waterfront property, so we destroy the marsh grasses and bulkhead the shoreline.
      3. population growth around the bay hurts water quality due to runoff from fertilizers added to lawns, and loss of filtering.
      4. So the services provided by the marshes are gone - now the sediment and nutrients that were once deposited twice a day on the marshes and so were absorbed by the grasses now remain in the water and are causing the demise of our seagrasses.
Animation of monthly changes in nitrates, oxygen, phosphate in the bay
Facts about the Chesapeake Bay- a summary
Chesapeake Bay Primer- another good summary
10 Ways for you to help clean the Bay

Maryland Sea Grant- Bay facts

Alliance for the Bay- fact sheets about rivers and concerns

The Chesapeake Bay Ecosystem- excellent summary document
State of the Bay-Chesapeake Bay Foundation
Pfiesteria links

Back to BSCI 124 main page

Last revised April 7, 1999 Straney