DO HALOPHYTOPHTHORAS (MARINE PYTHIACEAE) RAPIDLY OCCUPY FALLEN LEAVESBY INTRALEAF MYCELIAL GROWTH

Low estimates (2 . L(-1)) of concentrations of zoospores of Halophytop hthora in mangrove water columns seem counterintuitive when compared w ith rapid rates of occupation of fallen mangrove leaves (100% frequenc y of occurrence after 24-30 h). One potential explanation is that late ral extension of mycelium within leaves is rapid after establishment o f single zoospores. We tested this hypothesis by exposing single leave s in both mangrove and temperate salt-marsh ecosystems, with the upper half of leaves freely exposed to zoospore contact, and the lower half protected behind 8-mu m screening. We found no evidence that mycelial growth within leaves was rapid enough to account for the rapid occupa tion of freely exposed leaves. Of the four Halophytophthora species co mmonly found (H. kandeliae, H. masteri, H. spinosa var. spinosa, and H . vesicula), only H. masteri appeared to have substantial capability f or its zoospores to pass the screening. In temperate salt-marsh waters , H. kandeliae took the place of H. spinosa as co-occupier of leaves w ith H. vesicula. Two rare species (H. bahamensis and H. epistomium) or iginally described from subtropical mangrove environs were found in te mperate salt-marsh samples.