Marine mammals . Marine mammals are found principally in the marine 

 system and therefore are discussed in chapter 4, "The Marine System" and in 

 chapter 13, "Marine Mammals." 



Decomposers 



The decomposers are microbes, such as bacteria and fungi. They break down 

 dead organic matter and convert it to a form that can be recycled. These 

 organisms attach to, live on, and enrich detrital particles (dead organic 

 matter), making it nutritious for some consumers. 



Microbial decomposers have important roles in estuarine ecosystems. Bacterial 

 and fungal degraders comprise the largest group of living organisms in the 

 sea. In coastal waters, for example, from lO^ to 10^ bacteria/ml of sea water 

 can be found by direct counting techniques (Ferguson and Rublee 1976; and 

 Watson et al. 1977). In coastal sediments, from 108 to lOlObacteria/g dry 

 weight sediment (Dale 1974; and Novitsky and Watson, unpublished ) can be 

 found. Not all of these bacteria are decomposers or even living bacteria but 

 a large percentage of them contribute to the energy flow. 



In the estuary as well as in the open ocean, the most prevalent decomposers 



are Pseudomas, Vibrio , Flavobasterium , Anthrobacter , Caulobacter , 



Hyphomicrobriu , Cytophaga , Acinetobacter , and Photobacterium (Sieburth 1971; 

 and Leifson et al. 1964). 



Bacterial populations at Schoodic Point ranged from 10 to 1500 cells/ml on 

 marine agar (Pratt and Reynolds 1973 and 1974). Although no detailed 

 taxonomic study was undertaken, colonies isolated probably were representative 

 of the genera listed above. Results of counting bacteria using culture media 

 are usually several orders of magnitude lower than those found using direct 

 counting techniques, so that comparisons of published densities of bacteria 

 must be made with caution. 



FOOD WEBS 



The biological components of the estuarine system are linked to one another 

 through food chains or food webs. In this way, energy (food) is passed from 

 the producers (plants) to the herbivores (plant eaters) to secondary consumers 

 (animal eaters) to tertiary and higher consumers, and ultimately to the 

 decomposers. Each step in this progression is called a trophic level. 

 Organisms function at one or more trophic levels, i.e., a diatom is a primary 

 producer, a filter-feeding clam is a herbivore and functions on the second 

 trophic level, and crabs that eat both plant and animal material are both 

 herbivores and secondary consumers. 



From one trophic level to the next energy is lost; only a small part of the 

 energy contained within one level is passed to the next. In other words, 

 maximum energy is contained in the primary producer trophic level and 

 subsequent levels contain less and less. If we assume a 10% efficiency in 

 the energy transfer between trophic levels a great amount of energy from lower 

 levels is needed to support a top carnivore (e.g. bird, fish, or person). The 

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

 with discontinuous productive seasons (Gulland 1970). The Gulf of Maine could 

 fall into this category, although no specific information is available to 



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