The process by which plants utilize and store solar energy in the form of or- 

 ganic substances is called "primary production." The rate at which primary 

 production takes place is called "primary productivity" (Odum 1971). The 

 total amount of organic matter created is called "gross primary production." 

 Roughly 20% to 50% of the captured energy is lost in plant respiration, yield- 

 ing a net primary production of roughly one-half the gross primary production. 

 This net production results in the creation of plant materials that eventually 

 may be consumed by animals (herbivores and detritivores) . 



Energy is passed from producers to consumer organisms of different trophic 

 (feeding) levels through food webs. At the base of the food web are the pri- 

 mary producers: phytoplankton, benthic microalgae, and macrophytes (marsh 

 grasses, terrestrial plants, and macroalgae) . 



Plant eaters, or herbivores, occupy the next position in the food web, the 

 primary consumer level. Carnivores, which eat the herbivores, form the secon- 

 dary consumer level; and other carnivores that feed on the secondary consumers 

 occupy the tertiary consumer level. Additional levels of consumers may exist, 

 as well as an intermediate level of omnivores that feed on more than one level 

 of the food web. 



The following rules apply to energy transfer between trophic levels: 



1. Within each level in the trophic structure, energy is used for main- 

 tenance and growth. It is stored in the form of carbohydrates, fats, 

 and proteins and eventually passes to the decomposers through excre- 

 tion and death. 



2. Between one trophic level and the next, considerable loss (roughly 

 90%) of energy takes place. It is lost through consumption by organ- 

 isms in breathing, feeding, and reproducing, and in activities such as 

 migration, defense, burrowing, nest building, and courtship. 



Decomposers (bacteria, fungi, insects, and invertebrates) return inorganic 

 substances to the pool of available nutrients by oxidizing dead organic 

 matter. Waste products from the ecosystem (dead animals and plants, detritus, 

 and feces) are colonized by a succession of decomposers. Decomposers break 

 down organic material metabolically and return valuable materials to the soil 

 or water column. Nutrients are then recycled by primary producers to form or- 

 ganic compounds via photosynthesis. 



The flow of energy through the food web representive of a marine system in 

 eastern coastal Maine is illustrated in figure 1-5. The solid lines show the 

 direction in which energy flows. The sun (1), particularly during the summer 

 months, provides energy for the blooming of the phytoplankton. Phytoplankton 

 are the food of zooplankton (2), and both are the food of numerous species of 

 intertidal (3) and subtidal (4) animals, krill (e.g., euphausiids, mysid 

 shrimp; 5), and smaller fishes (6). Medium-sized fishes (7) feed on 

 euphausiids, mysid shrimp and smaller fishes, and all of these are food for 

 the Targer species, such as tuna and shark (8), whales, porpoises, seals (9), 

 people (10), and birds (11). When the larger animals die their bodies are ab- 

 sorbed rapidly into the system by scavenging starfish, urchins, sea fleas, 

 herring gulls, and other creatures. During life, all of the animals return 

 vital materials to the sea in feces. The nutrients (12) contained in feces 



1-7 



10-80 



