IV-77 



microbial life where sediments are constantly in motion or being 

 deposited. Where, however, such energy inputs do not dominate the 

 input of radiation solar energy, natural communities develop composi- 

 tions typical of Tropical, Temperate, or Arctic latitudes. 



Tropical systems (Figure IV. 1.31) are suoject to only slightly varying 

 warm temperatures; light energy input is both greater and more regu- 

 lar than in other latitudes. Within this general group there are the 

 sparse populations along coasts with deep clear water close inshore; 

 the teeming and colorful populations of coral reefs; and the man- 

 groves and the submerged grasslands associated with shallow, nutrient- 

 laden water. Only the southern part of Florida and the islands are 

 of this type. 



Arctic systems are subject to wide fluctuation of sunlight and temper- 

 ature but ice is the key factor. Ecological systems develop in, on 

 and under the ice and 1n the fjords associated with glaciers. (Figure 

 IV. 1.32). Only a small part of Alaska includes estuarine systems of 

 tnis type. 



Temperature systems are subject to moderate solar energy inputs, tem- 

 peratures tha.t change regularly with the seasons, and generally larger 

 tide ranges and more wave action than either tropic or arctic systems. 

 Most of the estuarine systems of the United States lie in the tem- 

 perate zone, and the balancing of solar energy input against mechani- 

 cal energy input in this zone leads to a great variety of ecosystem 

 types, even within small geographic areas. 



