Marine Science Chapters



Channel in the Salt Marsh
A channel in the salt marsh at low tide. The burrows of the crabs that live in the salt marsh are visible along the edge of the pickle weed.
Channel in the Mud Flat
A channel in the mud flat at low tide. The green along the edge is eel grass and sea lettuce.
Continuous water coverage makes life in the estuary channels easy when compared to life in the intertidal mud flat. Intertidal organisms, whether they live on or in the mud flats are subjected to daily changes in temperature and moisture. If it is raining at low tide they are further exposed to freshwater. The channels in an estuary may have some siltation but in general they are pretty stable areas. Lots of nutrients abound in the water because the channels are shallow and there is a lot of organic matter that decays (releasing nutrients) as well as the nitrogen fixing diatoms.

Eel Grass exposed at a minus tide
Eel grass, Zostera marina, often lives along in the mud flat channels and are exposed only at a minus tide.
Eel grass, Zostera marina, beds often cover the mud flat beginning about zero tide level (average low low water) and extend to some depth in the channels. These beds are homes to many species like the green sea hare, dove snail, kelp scallop, and pipe fish.

Eel Grass sea hare
An eel grass sea hare on a single blade of eel grass. The eel grass is about a half inch in width.
The green sea hare, Phyllaplysia taylori, lives right on the eel grass blades. It is so well camouflaged that it is nearly impossible to see unless you inspect the blades closely. This little sea hare lacks the purple ink produced by its much larger cousin that lives on the mud flat surface.

Dove Snail and Amphpipod
The dove snail (left) is often found in the eel grass beds along with its mimic - an amphipod (right).
The dove snail, Mitrella carinata, is a small brownish snail common on the eel grass in the channels. Its hard shell provides protection against predators. There may be a small crustacean amphipod in the same area, Pleustes platypa, whose coloration mimics the dove snail. This mimicry is thought to provide some protection for the small crustacean against predators who have tried to eat the dove snail and found it too hard.

Kelp Scallop
Kelp scallops (above) may be attached to the eel grass blades in the channels of the mud flat. Few are rarely over an inch across.
The kelp scallop, Leptopecten monotimeris, only gets to be 3/4 to 1 1/4 inch across. It is found attached to the eel grass blades in the channels.

The pipe fish, Syngnathus sp., come in shades of brown and green. They twist their bodies in the eel grass and look just like the blades of eel grass. These fish are related to the seahorses and the males carry the babies in a pouch on the front. They use the tiny opening, at the end of their long tubular mouth, to catch plankton from the water as it floats by.

Morro Bay Mud Flat at High Tide Morro Bay Mud Flat at Low Tide
Morro Bay mud flat at high tide (left) when most of the bay is covered with water. Morro Bay mud flat at low tide (right) when acres and acres of mud are exposed.
Mudflats are rapidly disappearing in California. This is because these estuarine areas are often targeted as wastelands and filled in to provide more area for homes and businesses. As scientists learn more about the unique biodiversity in these areas and their importance in the marine ecosystem destruction of salt marshes and mud flats has been discouraged and many of these habitats are now protected. The salt marshes, mud flats and estuary channels are now recognized breeding grounds for many marine birds as well as numerous sharks, rays, fish, and invertebrates.

Sunset at Morro Bay
Sunset at Morro Bay showing the breakwater which protects the entrance to the bay and Morro Rock.

 Copyright and Credits
(Revised 6 August 2007)
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