The 11 habitat types in the intertidal zone of the characterization area are: 

 mud flats, sand flats, sand beaches, gravel beaches, cobble beaches, boulder 

 beaches, protected rocky shores, aquatic beds, exposed rocky shores, emergent 

 wetlands, streambeds, and reefs. The habitat types that are most 

 characteristic of the estuarine system are gravel and cobble beaches, sand and 

 mud flats, protected rocky shores, streambeds, and emergent wetlands. The 

 other habitat types are discussed in chapter 4, "The Marine System," because 

 those habitats are unique to that system. 



The area of the intertidal subsystem is 66,382 acres (26,875 ha; see 

 "Introduction" for limitations of data). Acreages of the habitats of the 

 intertidal subsystem are given in table 5-2. The NWl class levels have 

 grouped some of the 11 habitats listed above. Beach/bar includes sand beach, 

 gravel beach, and cobble beach. Flats encompass areas of mud, sand, and 

 streambeds. Boulder beaches and exposed and protected rocky shores are 

 included in the NWl rocky shore class. 



Flats are the dominant (66%) intertidal habitat in the characterization area. 

 With the exception of the beach/bar habitats most of the other intertidal 

 habitats are distributed evenly among the regions. The beach/bar habitat is 

 more common in regions 4 and 6 than it is in the other regions. These areas 

 have many gravel and cobble beaches. 



Macroalgae and benthic invertebrates are the principal permanent residents of 

 the intertidal zone. At high tide fish from the subtidal zone move in to 

 forage and at low tide the intertidal zone is utilized by shorebirds, 

 waterfowl, wading birds, and mammals. The permanent intertidal residents are 

 mainly of marine origin. 



Physical factors affecting the distribution of organisms of the intertidal 

 subsystem are: tide, temperature, waves, nature and angle of substratum, 

 available sunlight, fog, and size of the intertidal zone. The intertidal 

 habitat is subject to a wide range of habitat conditions, ranging from extreme 

 low water spring to extreme high water spring (see "Hydrography," page 4-11 in 

 chapter 4) . The upward limit to which plants and animals can thrive in the 

 intertidal zone is determined by their capacity to adapt to periodic exposure 

 to extreme cold and heat, extreme drying action by the wind, and exposure to 

 fresh water (rain). 



The different tolerances of intertidal biota are indicated by their 

 distribution in bands parallel to the water line (zonation) . Zonation is a 

 general feature within the intertidal zone of the coastal area and can be 

 observed easily on a bedrock shore where all the organisms are attached to the 

 substrate surface. Few species tolerate the upper levels of the intertidal 

 zone. The ribbed mussel, for example, thrives so far up the intertidal area 

 that they are inundated only during a few high tides each month. 



Many invertebrate animals found in the intertidal zone are ubiquitous, that 

 is, widely distributed and able to live in a variety of habitats and tidal 

 heights. They also tend to be more resistant to human-induced and natural 

 stress. Invertebrate species common to estuarine intertidal areas of coastal 

 Maine are given in table 5-8. Oligochaetes and nematodes are dominant species 

 in all estuarine habitat types in the characterization area (Larsen and 



5-92 



