CHAPTER 6 



Natural History 



a. Feeding Habits 



Arbacia punctulata eats almost anything in an aquarium, and probably 

 does so in its native habitat. They have been observed eating Fucus, 

 Laminaria, Ulva, polyps of coral, sponges, mussels, sand dollars, and 

 other Arbacia, both the soft parts and the shell. Parker (1932) observed 

 and photographed two Arbacia eating diFundulus which "may be caught 

 and eaten by the sea urchins. The capture usually takes place at night, 

 and the prey is almost always a partly spent fish. I doubt if a fully 

 vigorous Fundulus is ever taken by a sea urchin. I have never witnessed 

 the first steps in the capture" (Parker, 1932P. 95;seealsoGudger, 1933). 

 Arbacia certainly cannot capture live fish, but eat them when moribund 

 or dead (E. B. H. observations for many years). For feeding habits 

 of A. punctulata and other sea urchins see van der Heyde (1922). 



Arbacia live well in aquaria supplied with Fucus and Laminaria and 

 shells peppered with holes containing the sulphur boring-sponge, C/zowa 

 celata, and of course with running sea water; some animals and plants 

 decay and pollute the water. Although they will eat almost anything 

 that is at hand, they can get along without food, except for the small 

 organisms brought in with the sea water, for several months. Two 

 sets of six Arbacia were kept in aquaria (capacity about four gallons), 

 one set in the dark and one set in the light, without being fed, for two 

 months. All individuals of both sets were perfectly healthy after that 

 period. 



The food for the developing pluteus is diatoms, especially Nitzschia 

 closterium which can be cultured with Miquel's solution (E. B. Harvey, 

 1949) or more simply by adding 0.002% Na2HP04i2H20 + 0.01% 

 KNO3 to sea water (see Part H). When the shell is developing, the 

 calcareous material can be supplied by the calcareous protozoon 

 Trichosphaerium and later by the red alga Corallina, according to Shearer, 

 de Morgan, and Fuchs (1914). 



