whales, the common dolphin, and the killer whale. The killer whale also feeds 

 on other marine mammals. 



The demersal and semidemersal feeders consume benthic fish (gadids, flounders, 

 and skates), molluscs, and crustaceans. This feeding group is dominated by 

 seals but also includes toothed whales to a lesser degree. Representative 

 species include the harbor seal, the gray seal, the harbor porpoise, and the 

 beaked whales. See chapter 13, "Marine Mammals" for a full description of 

 this group of animals. 



Decomposers 



The decomposers are microbes, such as bacteria. Their function in the 

 ecosystem is to break down dead organic matter and convert it to a form that 

 can be recycled. In so doing these organisms enrich detrital particles 

 (dead organic matter), making them suitable for some consumers. 



Microbial decomposers have important roles in marine ecosystems. Bacterial 

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

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

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

 Watson et al. 1977). In coastal sediments, from 10^ to 10^ °bacteria/g dry 

 weight sediment (Dale 1974; and Watson and Novitsky, unpublished ) can be 

 found. Not all of these bacteria are degraders or even living bacteria, but a 

 large percentage are and this fact reflects their importance. The most 

 prevalent genera are Pseudomas , Vibrio , Flavobasterium , Anthrobacter , 

 Caulobacter , Hyphomicrobriu , Cytophaga , Acinetobacter , and Photobacterium 

 (Sieburth 1971; and Leifson et al. 1964). 



Two limited reports exist for the bacterial populations of the Gulf of Maine. 

 Pratt and Reynolds (1973 and 1974) studied bacteria isolated on selective 

 media from Schoodic Point, Maine. Populations at Schoodic Point ranged from 

 10 to 1500 cells/ml when counted on marine agar. Although no detailed 

 taxonomic study was undertaken, the colonies isolated were probably 

 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 comparisons of published densities of 

 bacteria must be made with caution. 



FOOD WEBS 



The biological components of the marine system are linked by food chains or 

 food webs. Through food webs energy (food) is passed from the producers to 

 the herbivores (plant-eating species), to secondary consumers (animal-eating 

 species) and higher level 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 an herbivore and functions on the second trophic level, while 

 crabs that eat both plant and animal material are both herbivores and 

 carnivores . 



From one trophic level to the next a loss of energy takes place: only a small 

 part of the energy contained in one level is passed to the next. Maximum 

 energy is contained in the primary producer level and subsequent trophic 



4-41 



10-80 



