The brown algae dominate the biomass or bulk weight of rocky intertidal and 

 subtidal plant communities. In intertidal areas the brown alga Ascophyllum 

 and various species of Fucus (collectively call fucoids) commonly account for 

 greater than 90% of intertidal plant weight. These plants are commonly known 

 as rockweeds, bladderwrack, or knotted wrack. 



In subtidal areas the brown algae, Laminaria and Agarum (collectively known as 

 laminarians) , often dominate biomass. These laminarians, or kelp, extend from 

 low water marks to depths of approximately 30 to 60 feet (10 to 20 m) . 



Macroalgae require suitable stable surfaces, to which they attach themselves 

 for support. The large rockweeds and kelp need large stones or rocks that are 

 free of other flora and fauna for attachment. Areas lacking in stable 

 surfaces for attachment, such as mud, sand, or gravel, are generally devoid of 

 larger algae but may support relatively minor biomasses of small plants in 

 wave-sheltered areas. 



The convoluted rocky shore along much of the coast of Maine provides abundant 

 habitat for macroalgae, resulting in large, dense beds of plants. Seaweed 

 communities provide habitat for numerous marine and estuarine animals. The 

 growth of macroalgae is controlled by water temperature, salinity and the 

 availability of nutrients and sunlight, in addition to suitable substrata. 

 Macroalgae are consumed by grazers, such as sea urchins (e.g., 

 Strongylocentrotus droebachiensis ) , and fish. The amount of material consumed 

 is unknown but in areas that have periodic high densities of sea urchins, such 

 as Sheepscot Bay and Cobscook Bay, most plant material is consumed. 

 Reestablishment of macroalgal populations may require many years. 



Benthic diatoms . Benthic diatoms are similar in form to diatoms living 

 in the water column. However, these organisms live on bottom substrate in 

 intertidal and shallow subtidal areas. The size of the role this component 

 plays in the productivity of the marine system is undetermined. Benthic 

 diatoms on a mudflat in the Bristol Channel, England, had twice the 

 productivity of the overlying phytoplankton on a square meter basis (personal 

 communication from R. M. Warwick, Institute for Marine Environment Research, 

 Plymouth, England; September, 1977). Whether this factor of 2 can be applied 

 to similar habitats in other regions is not known. 



Benthic diatom productivity is consumed by invertebrate deposit feeders and 

 grazers, such as the common periwinkle and the mud snail. The degree of 

 dependence of such species on this food source is unknown but, in some 

 situations, it may be significant. 



Microbial producers . Microbial producers are bacteria and other 

 microorganisms that are suspended in the water column. They may be either 

 photosynthetic (i.e., dependent on light for growth) or nonphotosynthetic. 

 Little is known about the role or importance of these producers. It seems 

 likely that the large numbers of bacteria in open ocean water (10 to 10 

 cells/ml) are being utilized as a food source by planktonic feeders (personal 

 communication from T. Novitsky, Energy Resources Company, Cambridge, MA; 

 December, 1977). 



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