NO. 3652 ISOPODA AND TANAIDACEA 
MILLER at 
than four percent of them. By contrast, amphipods (notably caprellids) 
were found on 98.9 percent of the buoys sampled—about the same 
incidence as barnacles (Cirripedia). Other crustaceans, such as 
decapods and copepods occurred in a relatively small fraction of the 
samples—about the same as isopods. Reasons for these differences 
will be considered later. 
Another feature of the collection is the unequal representation of 
the seven isopod families (table 2). Between them, the Sphaeromatidae, 
Idoteidae, and Janiridae contributed 22 of the 26 isopod species and 
111 of the total of 115 occurrences by species, not to mention the 
predominance of individuals belonging to these three families. 
Several reasons or combinations of reasons may be advanced to 
account for the paucity of isopods and tanaidaceans in the collection, 
their low incidence on buoys, and the differences in frequency of 
occurrence of various crustacean groups: (1) inadequate sampling, 
(2) limited harborage presented by buoys, (3) difficulty of access, and 
(4) varying degrees of motility in different groups. 
The necessarily opportunistic sampling program and wholesale 
collecting methods are partly responsible for the deficiency of isopods 
and tanaidaceans. In some areas too few buoys could be sampled, 
and those sampled could not be selected for diversity of local ecolog- 
ical conditions. The number of species and individuals occurring on 
buoys would depend a great deal on the composition of attached 
fouling organisms that might serve for food, cover, or a temporary 
substrate for transient crustaceans. Some doubtless occur by chance 
encounter, but others may be attracted to the buoy and be induced 
to remain there by the type of fouling and associated organisms 
present; for instance, swarms of Synidotea laticauda on several buoys 
in San Francisco Bay doubtless were feeding on colonial hydroids. 
Species of Jdotea often were associated with kelp attached to buoys 
in temperate waters. Sphaeromatids tend to occur on buoys with 
“soft fouling’ (tunicates, bryozoans, hydroids, ete.) in bays and 
harbors. 
Greater variety and numbers also might have been obtained if the 
time and season of collecting could have been chosen. Buoys sampled 
a short time after cleaning or replacement, as some were, would not 
be expected to yield as many kinds and specimens as they might 
later when more heavily fouled. The season of sampling might also 
introduce sampling errors since the composition of fouling and associ- 
ated organisms may vary through the year as a result of seasonal or 
occasional variations in ambient water temperature, salinity, currents, 
turbidity, and other factors; hence, periodic sampling of buoys 
doubtless would give better results than single visits. 
