Associates of Marine Sponges — Long 
349 
sponge itself or to the mud collected thereupon. 
The fact that relatively clean samples of the 
sponge also harbored many associates indicated 
that there was a definite attraction to it. Other 
species of sponge occurring near or upon M. 
prolifera were completely devoid of associates, 
suggesting that the associates preferred M. 
prolifera. 
Halichondria panicea 
general observations: Halichondria pani- 
cea occurred as an encrusting sheet 1-5 cm thick 
upon unprotected rocky coast areas in violent 
surf. It was green in its upper layers and yellow 
below, the coloration being due to an intra- 
cellular single-cell alga. 
H. panicea harbored many associates of a 
great variety. A total of 6,098 organisms of 68 
species were found in 32 samples with densities 
of population of from 0.26 to 19-0 (mean 1.15) 
organisms per cm 3 . The most common associ- 
ates were amphipods ( Jassa falcata and caprel- 
lids); the barnacles Balanus glandula and B. 
nubilis; the isopods Dyndmene sheareri and D. 
dilata; and the coralline alga Corallina gracilis. 
The relationships of these associates to the 
sponges varied considerably. The associates can 
be grouped in four general headings : ( 1 ) those 
that were caught in the sponge as larvae and 
subsequently matured; (2) those that were on 
the sponge accidentally at the time of collection; 
(3) those that grew simultaneously with the 
sponge on the same substrate; and (4) those 
that clung to the sponge because it was abundant 
and provided purchase. 
Such organisms as algae, hydroids, ectoprocts, 
some crabs, barnacles, mussels, and some mol- 
luscs and annelids probably were caught among 
the sponge spicules as planktonic larvae and, 
having survived digestion, developed into adults 
thereupon and therein. Many of the nereids, 
large crabs, caprellids, gammarids, and fish 
were found by chance upon the particular sponge 
collected when they were feeding or using it 
for temporary shelter. It is most likely that 
some of the algae (e.g., Microcladia borealis ) 
grew simultaneously with the sponge. 
Several animals were grazing on the sponge. 
Acmaea asmi, Mopalia lignosa , Oedognathus 
inermis, Pachycheles rudis, Cancer product us, 
and, particularly Archidoris montereyensis were 
found to have H. panicea spicules in their 
stomachs. 
The only possible examples of truly mutual- 
istic associations were those concerning the 
intracellular algae of H. panicea and the clean- 
ing action of the Crustacea associated with H. 
panicea, as well as with Suberites lata and 
Microciona prolifera. The algae may have pro- 
vided needed oxygen or other nutrients to the 
sponge. The sponge without algae could sur- 
vive, but it usually appeared as thin, rubbery 
sheets. The numerous Crustacea fed on the 
material which collected upon the sponge. 
Generally, the samples of H. panicea from 
different areas harbored the same species, and 
the various members of the community were 
usually found in the same proportions from 
sample to sample. However, the exact composi- 
tion of the sponge communities varied enough 
among the samples to suggest that a given in- 
dividual community was related to the fauna of 
the immediate area. 
experiments : Sponges of similar consistency 
living immediately adjacent to Halichondria 
panicea normally had very few associates of any 
kind, while the clumps of H. panicea were well 
provided with associates. Also, when the nudi- 
branch Archidoris montereyensis was placed into 
a laboratory tank upon a piece of Suberites lata 
downstream from H. panicea, the animal would 
invariably crawl to the H. panicea, indicating a 
chemotaxis toward the H. panicea. 
An apparatus similar to that of Davenport 
(1950) was set up to determine if there was a 
chemical attraction of A. montereyensis to H. 
panicea. The apparatus consisted of a series of 
waterways which gave the nudibranchs a choice 
between water passing over H. panicea and Sub- 
erites lata. The majority of the nudibranchs al- 
ways moved toward the H. panicea water outlet: 
9 individuals of 15, 10 of 15, 13 of 15 in the 
three experiments went to the H. panicea outlet. 
None ever moved to the S. lata outlet. 
Homaxinella sp. 
This sponge had much the same shape as 
Microciona prolifera, but it was branched fewer 
times, and its branches were thicker and hollow. 
Homaxinella sp. occurred at a depth of 20-30 
meters off the Oregon coast. 
