12 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
desirable to protect the lobster larve against each other, against hungry alien enemies, 
and against starvation, until they show at least some signs of knowing how to care 
for themselves. 
2. DiatomMs on Losster LARVA. 
Well-lighted waters have many inhabitants, notably minute plants, and some of 
these show a tendency to attach themselves to the lobsterlings. This is especially 
true of certain forms of diatoms which normally grow attached to each other and 
to larger submerged plants. Mature lobsters confined in ponds and cars become the 
carriers of various animal and plant forms, which are not parasites but symbionts 
in the simplest degree, merely borne by the animal. The extent of the plant growth 
will naturally depend on the sunlight received by the lobster, copious growths of 
alge reaching to many inches in length developing on the antenne and other appen- 
dages, even on the eyes, when the animal has been confined for several months in 
shallow, muddy ponds. When such lobsters are removed to clean surroundings they 
gradually free themselves from all growths within their reach. Ordinarily the 
moulting process will completely remove all the effects of this symbiotic growth, but 
instances are known in which the rhizoids of the alge have penetrated the covering" 
of the lobster’s eyes, and moulting left the creature clean, but blind. 
The extent of the growth of diatoms on lobster larve is dependent on certain 
factors of which the three most important seem to be: (1) The amount of sunlight. 
received, (2) the extent of time between moults, and (3) the activity or inactivity 
of the lobsterlings. We have direct evidence of the truth of the first two of these, 
and indirect evidence of the third. During the summers of 1914 and 1915 Dr. A. P. 
Knight, for the Biological Board of Canada, has carried on rearing experiments at 
Long Beach, Digby county, Nova Scotia. The complete description of these 
experiments will be found in Dr. Knight’s reports for those years. The opportunity 
given the writer to study this interesting relationship between lobsters and diatoms 
was due to the kind invitation of Dr. Knight, who most generously placed all the 
resources of the station at my service. 
In both summers the lobster larve were loaded with a growth of diatoms which 
became 60 great as to cause the larve to sink to the bottom of the boxes in which 
they were confined. 
There they rolled about in the current caused by the movement of the stirring 
paddles, but were soon found to be dead. Their destruction was probably caused by 
exhaustion, and by starvation. The impeding masses of diatoms so clogged the 
mouth parts and the legs as to prevent the larve from securing food. 
Similar difficultiés were experienced by United States experimenters in lobster 
rearing at Wickford, Rhode Island, the diatom infesting the larve there being Licmo- 
phora tincta Grun. During the summer of 1914 the lobster larve in Dr. Knight’s 
care at Long Beach, Nova Scotia, were destroyed by Synedra investiens W. Sm., 
which normally grows on an alga, especially on Hctocarpus.. This formed almost 
the entire growth observable during that summer, the only other forms present 
being Cocconeis scutellum Ehr. and Lichmophora Lyngbyet (Kutz) Grun., and these 
were not plentiful. In 1915, however, it was the last-named species which took 
possession of the larvee and reproduced themselves so rapidly as to prove destructive. 
The following record will indicate the rate at which they became troublesome to the 
young lobsters. The figures represent only approximations, as in all probability 
some diatoms were in positions where they could not be seen. The lobster larve 
' were carefully scrutinized under a microscope, and care taken to make the counts as 
accurate as possible. 
