All ETDs from UAB

Advisory Committee Chair

Charles D Amsler

Advisory Committee Members

Robert A Angus

Bill J Baker

Kenneth H Dunton

James B McClintock

Document Type

Dissertation

Date of Award

2010

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

In the following dissertation, we explore benthic communities along the Western Antarctic Peninsula, specifically, interactions between the immense macroalgal and mesograzer assemblages and how these relationships are chemically mediated. Despite the widespread production of various chemical feeding deterrents throughout the macroalgal community, the system supports an abundant and diverse array of crustacean amphipods. Gut content analysis and stable isotopic signatures indicate that filamentous macroalgae and epiphytic diatoms probably play an important role as dietary constituents, despite their visible absence in the sub-tidal zones. Subsequent palatability and extract feeding assays revealed that none of the filamentous macroalgal material found in amphipod guts could be the result of direct grazing on any of the finely branched macrophytes, especially the finely branched rhodophytes which were all determined to be chemically defended against mesoherbivory. However, mesocosm experiments conducted under natural conditions determined that, if grazing pressures were removed, there would be a significant increase in both epiphytic diatom and filamentous algal coverage throughout the macroalgal community. Additionally, there would be a higher incidence of emergent filaments protruding through host macroalgal thalli from invasive endophyte colonies. Likely, the filamentous macroalgal material seen in the gut is the result of continuous amphipod grazing which keep endo/epiphytic biofouling to a minimum. Daytime versus nighttime amphipod density measurements indicate that several amphipod taxa have adopted a nocturnal foraging strategy. Collectively, amphipods are hiding among chemically defended macrophytes during the day while associating with more palatable species at night when the risk of predation from visual predators is decreased. Ultimately, we believe the dominant macroalgae and mesoherbivore assemblages are living in mutualism. The amphipods are taking refuge in the protective confines of chemically defended macrophytes during the day while continuously cleaning both palatable and defended macroalgae of potentially harmful fouling diatoms and filamentous epiphytes at night.

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