the re 

 This w 

 mass r 

 occur r 



The 

 and se 

 or m i n 

 specie 

 presen 



At 

 algal 



Algal 



c r u i t 

 as al 

 emove 

 ed on 

 fila 

 veral 

 i m a 1 . 

 s (Ch 

 t onl 

 this 

 s p e c i 



Prima 



ment 



so a 



d by 



the 



ment 



blu 



Pen 



ampi 



of th 

 ccompa 



micro 

 se pi a 

 ous sp 

 e-gree 

 nate d 

 a parv 



e g 

 n i e 

 -he 

 tes 

 eci 

 ns 

 i at 

 ul a 



Pro 

 treatm 

 per ch 

 betwee 



d u c t i 

 ents 

 1 orop 

 n gra 



y on 

 time 

 es o 



ry P 



these 



there 



c c u r r i 



roduct 



Pi 

 ap 



ng 



i on 



astropod C e r i t h i u m 1 i tt 

 d by an increase in the 

 rbivores (Table 1). Sma 



es Herposiphonia secund 



dominated plates where 



oms were also abundant. 



, C e r a m i u m n i t e n s and L 



a tes . 



pears 



under 



eratum onto the plates 



amount of algal bio- 

 11 filaments also 



a_, G i f f o r d i a r a 1 1 s i a e 

 herbivory was absent 

 Several 1 arger algal 

 a u r e n c i a obtusa ) were 



to be no clear pa 

 each type of graz 



on p 

 (Fig 

 hyll 

 zing 



er utii 



ure 2 ) 



a wei 



r e g i m 



t a 

 . W 

 ght 

 es . 



rea was not significant 

 hen expressed per unit 

 , productivity rates va 

 A consistent pattern o 



ttern in the number of 

 i n g regime. 



ly different between 



algal weight or 



r i e d widely 



f higher specific 



0.8i 



.C 

 I 



O 



Month 



Month 



Month 



Figure 2. Mean net community primary production + 95% confidence 

 limits; A) per area, B) per unit algal weight, and C) per unit chl. 

 a weight. (X)- all herbivore treatment. (□)- group 1 and 3 treat- 

 ment, (a)- group 2 and 3 treatment. (■)- group 3 only treatment. 

 (•)- no grazing treatment. J, J, and A on the x axis indicate June, 

 July, and August. Plates were submerged initially in December, 1981, 

 and these data were collected during the summer of 1983. 



production rates in urchin grazed treatments (all herbivore treatment 

 and urchin only treatment) than in fish grazed, micro-herbivore 

 grazed and non-grazed treatments, was mai ntai ned. Net specific com- 

 munity primary production rates (ug 02 ug chl. a' 1 hr." 1 ) differed by 

 a factor of two to four among the treatments, The micro-herbivore 

 grazed and ungrazed treatments had the lowest specific rates of algal 

 production. Specific rates were inversely related to algal standing 

 crop . 



DISCUSSION 



These data provide evidence that different herbivores have variable 

 effects on the benthic algal community. Data on algal species compos- 

 ition and specific primary productivity between treatments demonstrate 

 that functionally different herbivores have qualitatively and quanti- 

 tatively different effects on these parameters. Algal communities 

 grazed by Diadema apparently consist of algal species with much higher 

 specific rates of production. Such low biomass communities are main- 



116 



