Food Preference of Algivorous Invertebrates— Leighton 
105 
were determined by measuring loss in weight of 
algae after a feeding period. Data were tested 
statistically for consistency of ranks and for sig- 
nificant differences in means of consumption 
values. The method and its analysis are con- 
sidered to be an improvement over that reported 
earlier (Leighton and Boolootian, 1963). 
The following 11 common benthic inverte- 
brates, known to be exclusively or predomi- 
nantly macro-herbivores, were studied: 
Echmoids 
Lytecbinus anamesus Agassiz and Clark 
Strongylocentrotus franciscanus Agassiz 
Strongylocentrotns purpuratus ( Stimpson ) 
Gastropods 
Aplysia calif ornica Cooper 
Astraea undos a (Wood) 
Haliotis corrugata Gray 
Haliotis fulgens Philippi 
Haliotis mfescens Swainson 
Norrisia norrisii (Sowerby) 
Crustacea 
Pugettia producta ( Randall ) 
Taliepus nuttallii (Randall) 
The animals were collected from a variety of 
habitats and depths to insure that the results ob- 
tained would not reflect conditions imposed by 
the environment in any single habitat. Indi- 
viduals employed varied about an average adult 
size found in the field. During the years I960 
and 1961 at least 10 experiments were run with 
each grazing species. Numbers of animals in ex- 
periments ranged from 2 to 10 depending on the 
size of the particular species. 
The following seven species of algae were 
employed, representing the major noncalcareous 
plants available to grazers in southern California 
kelp beds in terms of biomass (Dawson et al, 
I960) : 
Phaeophyta 
Cystoseira osmundacea 2 (Turner) Agardh 
2 Halidrys dioica Gardner is indistinguishable from 
Cystoseira osmundacea when fruiting organs are not 
present (Dawson et ah, I960) and both forms have 
undoubtedly entered the experiments. The low pref- 
erence values observed for Cystoseira-Halidrys, in most 
cases, suggests there is no serious objection to the 
chance mixing of the two forms as one. Most experi- 
ments were performed in late winter, spring, and 
summer when fruiting organs permitted distinction of 
these two species. 
Egregia laevigata Setchell 
Eisenia arborea Areschoug 
Laminaria farlowii Setchell 
Macro cystis pyrifera (L.) Agardh 
Pterygopbora calif ornica Ruprecht 
Rhodophyta 
Gigartina armata Agardh 
Blotted fresh blades or fleshy thalli were cut 
either into pieces about 4 cm square or into 2.5 
cm discs. Equal weights of the seven algae were 
then thoroughly mixed and placed in experi- 
mental and control containers alike. In most 
cases the quantity of food provided aggregated 
70 g, comprising 10 g of each species. Larger 
grazers were offered twice this amount. The con- 
trols, containing algal pieces prepared in the 
same manner, but no grazers, provided a measure 
of any weight changes due to decomposition 
and/or imbibition. Experiments were of 24 hr 
duration. All algal pieces sank and remained on 
the bottom within easy reach of all the animals; 
pneumatocysts were excluded. 
A number of precautions were taken to assure 
uniformity in responses and to maximize ran- 
dom contacts between animals and seaweed 
fragments: 
1. Freshly collected algae were always used. 
2. A free flow of water was maintained con- 
tinuously in the containers. 
3. The algal pieces were thoroughly mixed 
several times during each experiment. 
4. Numbers of grazers and sizes of containers 
were selected so that each food species should 
be equally within reach of each individual. 
5. After one to three experiments, grazers 
were replaced by newly collected individuals. 
6. Between experiments animals were allowed 
to feed on a variety of algae but were subjected 
to approximately two days’ starvation immedi- 
ately prior to each experiment. 
7. Feeding experiments were suspended dur- 
ing times of unusually high ambient water tem- 
peratures. ( Algal deterioration was most evident 
at temperatures above 20 C.) 
At the end of a feeding period all remaining 
algal fragments were removed from each tank, 
segregated as to species, blotted free of adhering 
water, and weighed to the closest decigram. 
Weight losses, corrected for changes in the con- 
