Once a particular inter-habitat size pattern is determined, it is looical to 

 attempt to find an explanation for the pattern. Assume that a sampling study shows 

 that mean sizes of individuals (or colonies) change across habitats of increasing 

 wave exposure (e.g., Birkeland 1973, Ebert 1982, Sebens and Paine 1978, Sebens ms). 

 The following hypotheses (and probably others) could be proposed: 



1) mortality rates are higher in habitats with smaller individuals; mortality may 

 or may not be size-specific (greater for larger individuals). 



2) growth rates and thus maximum or asymptotic sizes are greater in habitats with 

 the larger mean individual sizes. 



3) recruitment rates of juveniles are greater in habitats with smaller individuals, 

 thus skewing the distribution and reducing the mean size. 



4) fission or colony fragmentation rates are higher where the individuals or colo- 

 nies are generally smaller. Biomass growth could still be as high or higher 

 than in other habitats, but must be considered as 'clonal' growth rate. 



A variety of experimental and monitoring approaches must be undertaken to test such 

 hypotheses. Furthermore, the above hypotheses are not mutually exclusive nor are 

 they comprehensive. All of the above causes could influence the size pattern in the 

 same direction. The following discussion will explore the second hypothesis. 



Figure 1 A. Shapes of hypothetical size-frequency histograms. 



B. Diameters of the octocoral Alcyonium in three habitats (Sebens Ms.) 



C. Mean sizes of Alcyonium versus wave exposure index (elevation of intertidal 



Mean sizes of Alcyonium versus wave exposure index 

 barnacle zone) (Sebens MS) , DIA = average colony diameter 



D. Sizes of 10 laroest sea anemones ( Phymactis clematis) as 

 exposure index (Sebens and Paine 1978) , DIA = basal 



a function of wave 

 diameter, mm. 



20 



10 



80 



60 



DIA 



40 



cm 



20 



A SKEWED 

 M LEFT 



GAUSSIAN 



SfZE 

 r> PROTECTED 



10 



J^ 



SKEWED 

 RIGHT 



J 



n 



MODERATELY 

 EXPOSED 



£ 



10 



20 40 60 80 20 



DIA cm 



C 



10 



n 



BIMODAL 



EXPOSED 



n^lr^rL, 



40 60 80 20 40 60 100 



M 



10 1.5 2.0 2.5 12 3 4 5 6 T 



EXPOSURE INDEX 



10 



