The Interaction between Epiphytes and Seaweeds

Two Israeli laboratories (IOLR and TAU) cooperated with one American laboratory (USF) in the research of the interaction between epiphytes (Ulva sp.) and the cultivated seaweed (Gracilaria sp.) The main objectives included the following aspects: Structural aspects, effects of different irradiances on growth, sensitivity studies, allelopathic excretions, selective chemicals and integration of studies of epiphytization. The studies were operated in outdoor tanks, indoor growth chambers and in the lab. The main conclusions and their relevance for mariculture are as following: 1. The green algal epiphyte, does penetrate its red algal host. 2. Gracilaria spp. in monoculture released more halogenated hydrocarbons than in biculture with U lactuca, whereas other metabolic parameters did not show a discriminating effect in biculture. 3. Hydrogen peroxide and halogenated hydrocarbons could be a part of the effective excretion compounds in biculture. 4. The presence of mature Gracilaria inhibited the growth of U. lactuca sporelings. 5. G. conferta is most sensitive to epiphytes among Gracilaria species tested. 6. The use of green light can enhance growth in basiphytes but inhibit epiphytes. 7. Effective selectivity has been defined by the use of hydrogen hypochlorite. 8. It may be more profitable in seaweed mariculture to select for epiphyte resistant strains than to search for inhibitors of epiphytization. 9 It is important as well to examine how the basiphyte may be able to prevent penetration. 10. Definition of the effective excretions in biculture has still to be done.