字幕表 動画を再生する 英語字幕をプリント We are here at Folgers Marsh on the island of Nantucket and we are going to talk about what a salt marsh is. Salt marshes are communities of grass - and the animals associated with them - that form in quiet embayments between the high tide low tide marks. It is an interesting habitat because it is both an aquatic habitat - flooded with salty water - and a terrestrial habitat. When the tide comes in - as we see here at high tide - the water moves over the surface of the grass and is partially an aquatic habitat. The grasses are experiencing salty-water, which is not a great condition for them. But these grasses are adapted to tolerate it. Animals move onto the marsh and get some protection from predation. Things like little shrimp and little fish can move onto the surface of the marsh. There is a gradation of species on the marsh - from this edge or this low tide or low marsh mark to the high tide mark as you move back. At the edge we have this species called 'Spartina alterniflora' - or salt marsh cordgrass. It can grow pretty tall in some areas, and as you move back onto the marsh it stuts. It is most covered by the tide for the longest period of time - tides come in and out on a six hour cycle twice a day. It can tolerate being flooded by water because it has aerial roots. Plants take in oxygen through air not their water. The animals that live on the marsh however, most of them are aquatic animals. Things like mussels and fiddler crabs. They get oxygen from the water. I am going to talk a little about the animals in the marsh. You can see there are birds feeding. This is [an] important habitat for feeding - things like egrets, herons and osprey. The water that comes in through the marsh channels - and flows throughout the marsh - is [an] important habitat for crabs and smaller juvenile fish of some commercially important species such as flounder and bluefish. We also have smaller species that are salt marsh creek inhabitants that provide food for the crabs and the other larger fish. At the edge of the marsh there is a mussel that is attached to the substrate and to the roots of the 'Spartina alterniflora'. This mussel called the ribbed mussel - 'Geukensia demissa' - has a mutualistic association with the grass. It provides nitrogen and stabilizes the roots, while the plant provides a place for it to attach to - and a little bit of protection from predators. You also find fiddler crabs. Fiddler crabs make little burrows along the edge - and there [are] actually three species of fiddler crab that live in this marsh. Some live in this more sandy habitat another species lives in more muddy habitat[s]. As you go back through the marsh towards the road there is actually a source of fresh water, and you get a third species that lives in that more brackish water - or less salty water. Fiddler crabs make burrows, and this burrow help aerate the substrate. One condition of a marsh is that when it is flooded you have a lot of microbial action going on. It depletes the water that is in the sediment of oxygen. As you move back - if you were to dig a hole and let it fill with water - that water would be very smelly because of the microbial action - sulfur. It also would have very little oxygen if any oxygen at all. This is also a physiological stress for plants and animals. So you can see [that] a salt marsh is a very unique community of plants and animals that live in this area the coast. It is an important habitat, it is a habitat that provides a lot of primary production. Which means the grasses take in carbon dioxide and turn that into organic carbon. It also is an important habitat for the coastline behind it. It provides protection from storm damage [as] a buffer zone between the sea and the land. Thirdly, it is an important habitat for these important commercial species and juvenile fish that use the salt marshes to grow larger - they use the food provided by the other smaller organisms that eat the detritus provided by the plants.