ECOLOGY AND TAXONOMY OF HaUmeda 167 



development of new organisms from released zoospores or gametes, are 

 of minimum help in controlling attached organisms, a number of which 

 reproduce by non-motile means. 



Other methods tried include the use of the invertebrate poison 

 Lindane, and the antibiotic Penicillin. Lindane had previously been 

 found helpful in Ulva culture (Strand et al., 1966). Halimedae were 

 immersed for 15 minutes in seawater containing Lindane at a concentra- 

 tion of 15 parts per million. The results for the limited number of thalli 

 available for experimental treatment were inconclusive. 



For the testing of Penicillin the antibiotic was added to two aquaria 

 at a concentration of 1000 units ml"^ for one and 3000 units ml"^ for the 

 other. The higher concentration killed the vegetative stage of many 

 epiphjrfces and they dropped off within the first two weeks. By the end 

 of about two months, however, epiphytes, particularly blue-greens, 

 were again abundant (Hillis-Colinvaux, 1972). When the treatment was 

 repeated, it was not as effective. Penicillin may be helpful in short-term 

 epiphyte control, particularly if added to the medium initially. 



8. New approaches to epiphyte control 



Two additional techniques could be helpful. Sand-growing species 

 might initially be planted in trays which could then be transferred out 

 of one aquarium to a cleaner one, or used for experimental purposes. 

 The trays could also be suspended over bottom filters smce the circula- 

 tion pattern would not then interfere with any reducing environment 

 established by the holdfasts in the trays. 



Epiphjrte-free stock also can provide cleaner cultures. One source of 

 such plants is the young Halimedae developing in the aquaria by vege- 

 tative multiplication. They can be successfully transplanted into fresh 

 aquaria. Another potential source of clean thalli are mdividuals pro- 

 duced by regeneration. The basic procedure is to remove branches of 

 several segments from robust thalli by cutting at the node (where there 

 are fewer filaments), briefly pressing the cut ends together to induce 

 wall formation (Jacobs, 1958), thereby preventing excessive loss of 

 cytoplasmic materials, and then anchoring or planting the cuttings 

 in substrate. I have had limited success with such cuttings which have 

 ranged from two to a dozen segments. The longer cuttings were the 

 most successful, and although none grew into a large thallus (all tended 

 to get overgrown with epiphytes), a few produced new plants from 

 rhizoidal runners in the sand (Section VII), and others produced rhizoids 

 and segments. 



