Community analysis of epiphytic diatoms from selected species of macroalgae collected along the Texas coast of the Gulf of Mexico.




Medlin, L.K.

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Texas A&M University.


The epiphytic diatom community represents one of the least well known benthic diatom assemblages, especially in terms of species composition and seasonal variation. The present study investigated the epiphytic community structure associated with selected species of macroalgae along the Texas coast of the Gulf of Mexico using community composition statistics, multivariate analyses, scanning electron microscopy. This study represents the first investigation of epiphytes diatoms from this area, as well as the first seasonal study of epiphytes over a two year period in the western hemispere. Because it was a baseline study of this flora, questions as to which species were present, how they varied seasonally, and what variations could be correlated with environmental changes or with the host plant itself were addressed Samples of host plants were collected at two month intervals from granite jetties at Galveston, Port Aransas, and Port Isabel, Texas. a wash, tip, and base preparation from each host plant was processed for statistical analyses. Community composition statistics revealed that the diatom assemblages washing off the host plants were statistically different from those attached to the host plant during the fall and spring. During the winter, the diatom assemblages associated with the host plant were more alike. The variation between the different species of host plants was greater than the variation between replicas of the same host plant, especially at Galveston and Port Aransas. There was a subtle seasonal change with ten taxa comprising 50-60% of the flora in the spring. The community gradually changed so that only three taxa were dominant in the winter. Multivariate analysis demonstrated that there was a continuum in the diatom community down the coast southward from Galveston to Port Isabel that could be weakly correlated with increasing salinity. A distinct change in abundance of epiphytes could be demonstrated among the host plants as branching increased. Abundance and diversity also increased distally from the tip of the host plant. The increased diversity of the wash often help mask the host-related differences in the attached assemblage. The microdistribution of the epiphytes as they relate to both host plant shape and increasing distance from the actively growing meristem was documented with the use of scanning electron microscopy.


150 p., Dissertation


diatoms, community composition, abundance, seasonal variations, microbiological analysis, statistical analysis, baseline studies, environmental effects