Sept. 24 Marine Wetland Plants - temperate salt marshes - dominated by grasses. mangals - mangrove ecosystem. seagrasses - submerged plants. All three habitats are very productive, they are critical habitats for fish birds, and crustaceans, and are threatened habitats because they are rapidly depleting. Mangals and temperate salt marshes are usually found where a river enters the sea . Sediments are deposited here and a shifting delta is built. This area is colonized by mangroves in the tropics (mean 20 degrees C) and salt marshes outside of the tropics (>20C). There are 2-3 million ha of coastal wetlands, about half of this area is mangroves and the other half is salt marshes. The total salt affected soil is 400 million ha (inland and coastal). About 46 million ha of salt affected area is manmade from irrigation. Marine higher order plants are called halophytes (halo = salt, phyte = plant). Non-tolerant plants are called glycophytes. Halophytes evolved from glycophytes, first to coastal habitats and then inland. Most of the inland forms have coastal relatives. Halophytes are not a single taxonomic group - this classification includes grasses, shrubs, trees, and succulents. There are 20 families, with 2000-4000 species. The degree of salt tolerance varies in each of these families. There is not a precise measurement for salinity because seawater has a mixture of salts. 85% of seawater is NaCl. Seawater is also composed of MgSO4 (Epsom salt), CaSO4 (plaster of Paris), bicarbonate, and KCl. The units for salinity measurement are: 1. ppt - g/L total salts. There are 32-35ppt in the ocean, and 40ppt in desert seas. 2. moles/L - The molecular weight of NaCl is 58, seawater has 500-600mM. 3. pressure units - the osmotic pressure effect. Distilled water has 0MPa, seawater has - 2-3Mpa. (1 Pa = 1 newton/m2 .) Pressure can also be expressed in bars, seawater is measured to be 20-30 bars. 4. Electrical Conductivity (EC) - a measurement of how well electricity conducts through water. Seawater has 60 dsm. Mechanism of Salt Tolerance: The problem with seawater is that Na is toxic to cells, and salty water has low water potential. In normal cells the water and solutes inside give the cell turgor and water continues to move into the cell because there is a lower water potential inside. In seawater, the lower water potential is on the outside and water leaves the cell. This creates small, shriveled up cells. Halophillic bacteria can take seawater into their cells because they have developed enzymes that can tolerate salt. Algae cells make organic compounds to lower their water potential, which keeps the salts out. Algal enzymes are not at all tolerant of salts. Higher halophytic plants have developed a vacuole inside of their cells which will keep NaCl contained, while the cytoplasm has only organic solutes and a low NaCl concentration. Emergent plants face a special problem due to the large amount of water flowing through them and high transpiration rates. The amount of water that a plant needs to process for growth is 200-500g per g of dry matter. (200 g for C4 plants, 500 g for C3.) It seems that any amount of salt in the water would load the plant with salts. It does not happen this way, plants have developed a very efficient system for filtering out salts at the root system. 99% of the salt is excluded from the plant, and what does get in is put in vacuoles. Characteristics of Halophytes: 1. Exclude most NaCl efficiently from roots. 2. Many are C4 (requiring less water). 3. Can store NaCl in cell vacuoles, especially in the leaves. 4. Can excrete salts into the leaves through salt glands or bladders. 5. Can become succulent to dilute or concentrate NaCl as needed. Temperate Marshes: Spartina (cordgrass) dominates the east and west coasts of North America, making up the main marsh system of the coastal US. S. foliosa is found on the west coast, while S.alternifloria (smooth cordgrass) and S. patens (short cordgrass) are found on the east coast. The reason these species are of so much interest is their high productivity. Spartina supports a detrital food chain. Eugene Odum has done a lot of work with Spartina and has developed the concept of tidal energy subsidy. Odum measured the productivity of Spartina and found 750 g/L2 in the high intertidal zone, 2300 g/L2 in the intermediate zone, and 4000 g/L2 in the low intertidal zone. This productivity is as high as any agricultural crop, even though Spartina faces low levels of nutrients, high salinity, and anaerobic soil. The tidal energy subsidy theory explains that tidal action brings oxygen and nutrients to the plant as well as flushes salts deposited on its leaves. 2 interesting cases of S. altternifloria: 1) In the 1970's this species was brought to the south San Francisco Bay area. It quickly spread all of the way up to Puget Sound, replacing all of the low growing halophytes. Now the coast is dominated by Spartina marshes. 2) In the late 1890's Spartina was brought to a marsh in Poole, England. It spread and then crossed with a local species S.maritina to make a male sterile hybrid S.townsendii. The new species spread vegetatively and doubled its chromosomes to produce another species S.anglica which is fertile. All of these species have taken over England's marshes. Sept. 26 More on salt marshes and mangroves. Associated species in salt marshes are species that grow in fronts or pockets of the dominant species (usually spartina). Positive estuaries have a river at the back and get less saline going away from the sea. The true halophytes are found at the front, less salt tolerant wetland plants are found at the back. In a positive estuary the back zone is colonized by Juncus, Scirpus, and Phragmites. The middle zone is dominated by Spartina or mangroves, with patches of halophytes like Batis and Salicornia. The front is colonized by annual Salicornia before Spartina can get going, this is because Salicornia can easily colonize mud flats. Negative estuaries are like the Colorado River delta with no current river flow. These areas are saltiest near their backs. In a negative estuary, the back zone is covered in Allenrolfia, Atriplex, and Distichlis. The front zone has algae and seaweed as well as Salicornia. A salt marsh will typically only have about a dozen species living in it. In the Gulf of Mexico, the species that are found are Distichlis palmeria (Nypa grass), and Salicornia bigelouii (a succulent annual) in the low zone. The middle zone is occupied by the bushes Salicornia subterminalis and Salicornia virginica. There are also the ground covers Patis maritima, Cressa truxillensis, Suaeda esteroa, Atriplex barclayonia, Frankenia grandifolia, and Monathochloe littoralis. In the high zone larger bushes are found such as Atriplex canescens, Allenrolfia occidentalis and Suaeda torreyana. Mangroves are trees in salty, saturated soil. There are two big groups of mangroves with only one similar species. Mangroves are found in tropical regions between the Cancer and Capricorn tropics. The western group has only 8 species and the eastern group has 40 species. In the west the species are found in the genera Auicennia germinaus, Rhizophora mangal, Rhizophora racemosa, and Lagoncularia racemoas. In the east, the genera are Auicennia marina, Rhizophora mucronata, Lumitzera, Nypa, and several others. The speciation of mangroves is the same as that for seagrasses and corals. Distribution happened 70 - 135 million years ago in the Cretaceous period, also the age of dinosaurs. Laurasia was the center of origin for the mangroves, and when the continents divided few made it to the west. Today nearly all of the species are found in the east , which also has the richest flora.