Macroalgae. The physical and chemical factors that control macroalgal 

 productivity are varied and may differ substantially between species, with 

 most plants responding to several factors at one time. Factors governing the 

 productivity of marine macrophyte communities are the availability of light 

 and suitable substrata; suitable salinity levels and water temperatures, and 

 an adequate nutrient supply. Tides carry life-sustaining compounds to 

 intertidal macroalgal populations. 



Growth of the dominant intertidal alga, Ascophyllum nodosum , is limited by low 

 temperatures. Even high light levels (apparently necessary to approach 

 photosynthetic saturation) do not initiate rapid growth below 5CP F (10 C) . 

 Generally, higher summer water temperatures can be expected to yield greater 

 productivity than lower winter temperatures. Also, stress associated with 

 freezing during winter probably depresses growth. Increased grazing activity 

 is an indirect effect of warmer summer water temperatures (approximately 68 F; 

 20 C) in Maine. Much of the coast of Maine has suitable substrata and 

 salinity conditions for the development of A. nodosum . 



Factors such as ice scouring, wave action, and grazing, which dislodge or 

 consume A. nodosum, increase the rate of turnover of algae, thus, increasing 

 net production. Wave action is also a factor in determining the distribution 

 and abundance of macroalgal species. Certain species thrive in areas of 

 increased wave action (e.g., Fucus sp . ) , while others are more abundant in 

 protected areas (e.g., Ascophyllum sp . ) . Greater wave action and steeper 

 shores promote the development of more ruggedly constructed plants that are 

 resistant to wave drag and abrasion. Biomass per unit area also tends to be 

 somewhat lower along the high-energy, wave-exposed shores at the headlands and 

 islands in coastal Maine than in more protected areas. In the sublittoral 

 zone wave action exerts influence only at the uppermost levels. 



Populations of subtidal laminarians (the dominant subtidal alga) are 

 restricted to areas of suitable substrata and relatively high salinity. Light 

 availability greatly influences their growth as is true of many subtidal 

 plants. Therefore, laminarians grow only in shallow subtidal areas (to 60 

 feet; 20 m) , where light is most available. Clarity or turbidity of the water 

 also affect their growth; algal penetration increases with clarity. High- 

 intensity solar radiation in summer may discourage the growth of some light- 

 sensitive plants, especially at shallow depths. In contrast to the intertidal 

 fucoids, which grow better at high temperatures, laminarians grow quickly at 

 low water temperatures and appear to show ill effects at higher temperatures, 

 approximately 68 F (20 C) . Their major growth period begins in winter and 

 continues into spring. In addition to the possible stress of higher summer 

 temperatures, lack of available nitrogen (see "Nutrient Cycle" above) may 

 limit summer and fall kelp productivity. 



Zooplankton . Temperature, along with food availability, is the principal 

 factor responsible for the succession of zooplankton species that occurs in 

 nearshore waters of coastal Maine. Each species has a particular temperature 

 range in which growth, reproduction, and survival occur. As one group 

 disappears, another appears and overall production is maintained throughout 

 the year, despite annual temperature ranges far exceeding the reproductive 

 tolerances of either group. In areas of freshwater discharge, such as upper 

 Penobscot Bay, certain zooplankton species appear to be unable to reproduce 



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10-80 



