S— Continued 



seaweed zonation— Zones of algal growth 

 related to mean tide level. Usually desig- 

 nated by type of algae: (1), green sea? 

 weed growing in pools near Or slightly 

 above high water mark (Enteromorpha); 

 (2), brown, mostly intertidal (Fucus); 

 (3), red, shallow waters offshore or at 

 the bottom of deep rock pools. 



secondary succession — Succession which 

 starts in an area where the previous 

 community was destroyed (e.g., by fire, 

 flood, etc.). 



sediments, marine -littoral 

 littoral sediments. 



See 



sere— A stage in succession to the climax 

 community. 



serology— The study of the development of 

 a climax community and the stages that 

 lead to it. 



sessile— An organism which usually is fixed 

 but may move infrequently or may be 

 permanently attached. 



seston— Refers to all material, organic and 

 inorganic, suspended in the water 

 column. See also tripton. 



shellfish— Any aquatic invertebrate with a 

 hard external covering; more commonly 

 mollusks and crustaceans. 



spat— The larvae of young bivalve mollusks 

 just after settling. 



spawn— To produce or deposit eggs or 

 sperm (verb). Also the young produced 

 (noun). 



species— An aggregate of interbreeding pop- 

 ulations that under natural conditions is 

 reproductively isolated. 



species diversity index— The ratio between 

 the number of species in an area and the 



importance values (e.g., numbers, bio- 

 mass, productivity) for each species. 

 There are several formulas for species 

 ». diversity indices varying primarily in the 

 determination of the importance values. 

 Each index has its own advantages and 

 limitations. See also Diversity. 



specific density— See density. 



splash zone — The zone immediately land- 

 ward of the mean higher high water level 

 affected by the wave spray. See also 

 supralittoral. 



spring maximum— Occurrence of abundant 

 phytoplankton (predominately diatoms) 

 after a winter minimum. The production 

 of phytoplankton is generally the highest 

 for the year during this period. 



standing crop— See biomass. 



standing stock— See biomass. 



steno— A prefix referring to a narrow range. 

 Opposite of Eury. 



subclimax— Usually refers to a stage or sere 

 before the climax. 



sublittoral zone— (1) In lakes, the region 

 below the area of rooted vascular plants 

 extending to the profundal zone (deep 

 bottom). (2) In the oceans, the region 

 extending below the intertidal to the 

 edge of the Continental Shelf. 



submergent vegetation— Plants which grow 

 primarily under the water surface. 



succession— In an ecological sense, an 

 orderly process of community develop- 

 ment and changes with time, which 

 results from interactions between species 

 and environment. See also ecological 

 succession. 



16 



