levels contain less and less. For example, a four trophic level pelagic food 

 chain consists of phytoplankton, zooplankton, zooplankton-eating fish, and 

 predaceous fish. Each trophic level feeds on the one below it and the 

 predaceous fish are harvested by people. If we assume a 10% efficiency to the 

 energy transfer between trophic levels, a great amount of energy is needed to 

 support a top carnivore (e.g., bird, fish, or people). The transfer 

 efficiency is probably higher than 10% to 12% at higher latitudes with 

 discontinuous productive seasons (Gulland 1970). The Gulf of Maine may be in 

 this category, although sufficient specific information to make 

 generalizations about energy transfer efficiencies is not available. Using 

 the 10% assumption, to produce a pound (.45 kg) of commercially utilizable 

 fish, 10 lb (4.5 kg) of smaller fish are required as prey. The support of 10 

 lb of small fish requires 100 lb (45 kg) of zooplankton, which in turn consume 

 1000 lb (450 kg) of phytoplankton (figure 4-13). In other words, even a 

 simple food chain must contain a large amount of energy at the lowest level in 

 order to support the higher trophic levels, which have progressively less 

 energy available. 



A more realistic and still simple marine food web is shown in figure 4-14 from 

 Mills and Fournier (1979). This model is based on the Nova Scotian fishery 

 and shows yearly productivity levels for each component, as well as the 

 pathway of energy flow among the components. It demonstrates the process by 

 which the energy of primary production is transferred and utilized, so that 

 only a small amount reaches the higher trophic levels where it can be utilized 

 by people. 



A sample series of food chains organized into a marine food web is shown in 

 figure 4-15. The species included, which are representative of larger numbers 

 of species, are arranged according to their approximate trophic level. 



PHYSICAL/BIOGEOCHEMICAL/BIOLOGICAL INTERACTIONS 



Energy Cycles 



Marine productivity is higher in coastal areas than in offshore areas. 

 Nutrients from land runoff and nutrient regeneration from the bottom can be 

 utilized by the primary producers in shallow coastal waters. Largely for this 

 reason the major fisheries of the world are located on continental margins. 



In the following discussions material is used from studies conducted outside 

 coastal Maine. In Maine, research has been limited to the study of primary 

 production by phytoplankton, and no investigations have addressed energy flows 

 or the energy requirements of higher trophic levels. 



A schematic diagram of the functioning of the Maine marine system is shown in 

 figure 4-16. This figure represents biological food webs but also integrate 

 the abiotic forcing functions. 



The two major productive elements in the Maine coastal marine system are the 

 phytoplankton and macroalgae. Benthic diatoms may be locally important in 

 some intertidal areas. Insufficient nutrients often limit the growth of these 

 plants; therefore, importation and recycling of nutrients, especially nitrate, 

 are necessary for high productivity. 



4-42 



