Population and community ecology of the red alga Rhodomela larix (Turner) C. Agardh, on the central Oregon coast Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5h73pz87f

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  • Aspects of the life history and ecology of the intertidal turf-forming alga Rhodomela larix (Turner) C. Agardh were examined over a two year period at several sites on the Oregon coast. Rhodomela occurred over a broad tidal range and exhibited different growth and morphology characteristics with respect to tidal height. Growth was most rapid in spring and summer for mid and low zone sites. A large amount of variation in growth occurred both between and within sites. Within site variation was partially explained by diversity in the age of erect portions of thalli within a given plant. Basal portions of post-reproductive axes may be retained by a plant without directly contributing further to reproductive output. Male gametophytes (haploid) begin developing early in spring, and appear to be restricted to mid and high intertidal areas. Tetrasporophytes (diploid) and fertilized female gametophytes (cystocarps) follow later in the spring and continue to be produced into the fall. Despite the extensive development of reproductive structures, little recruitment was observed. Rhomomela regained dominance following removal by vegetative proliferation from surrounding plants and through regeneration from microscopic basal cells. Many epiphyte species were found in association with Rhodomela larix. Peak abundance of larger forms occurred in the late summer. Several of these species were shown to have a negative affect on the growth and survival of Rhodomela axes. Epiphytes were utilized by herbivores living within the beds of R. larix as a food source. The gastropod Littorina scutulata and several species of gammarid amphipods consume diatoms from the surface of Rhodomela. Amphipods were shown to significantly decrease the growth of epiphytic, chain-forming diatoms on R. larix in laboratory tanks. Rhodomela larix reaches maximum abundance on low zone benches subjected to sand scour and/or burial. Laboratory experiments confirmed that Rhodomela can survive at least three months of burial in fine grained, anoxic sediment. Epiphytes and several species of saxicolous algae were eliminated by sand coverage both in the laboratory and in situ. In addition, large herbivores were absent from sand-swept benches where Rhodomela was common. Thus it is hypothesized that sand may benefit Rhodomela by (1) eliminating potential competitors and epiphytes and (2) eliminating large herbivores which might otherwise consume the plant. The life history and morphology of the plant contribute to its success in sand-influenced habitats.
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