COMPETITION AMONG MANGROVE OOMYCOTES, AND BETWEEN OOMYCOTES AND OTHERMICROBES

Competition experiments were performed using precolonized leaves or le af disks of red mangrove Rhizophora mangle with: (1) disks containing pure cultures of single species of marine true fungi or species of Hal ophytophthora (the principal genus of marine oomycotes); and (2) leave s bearing bacterial films. Preoccupied leaves were exposed to natural microflorae in mangrove creeks at 2 Gays in the Bahama Islands, or pla ced in laboratory seawater enclosures wherein pairs of halophytophthor as were given equivalent opportunity to occupy fresh leaf material. Th e ubiquitous coastal-marine oomycote H. vesicula was found to be an ab le competitor versus true fungi and versus other halophytophthoras. Ag ainst other halophytophthoras, this was true for both primary and seco ndary resource capture. The one exception among the fungi was a specie s (Dendryphiella salina) common in decaying drift material in high-int ertidal zones. H. spinosa was a weak competitor with true fungi and wi th H. vesicula, though it was not displaced by H, vesicula, and H. spi nosa could depress the frequency of H. vesicula occupation when H, spi nosa was well established. H. bahamensis did not routinely form sporan gia, preventing identification and firm conclusions regarding competit iveness, other than that it could not block H, vesicula, but could blo ck H. spinosa from entering its occupied arenas. When bacterial films were present on leaves prior to access by halophytophthoras, the occup ation frequency of halophytophthoras was sharply depressed (by about 7 0 to 90% with 48 h bacterial films), including for H, vesicula, implyi ng that in some types or parts of mangrove systems, submerged-leaf dec omposition may sustain low levels of participation by halophytophthora s.