I investigated the ecological functions of halogenated secondary metabolites from the red alga Asparagopsis armata, their localisation in specialised cells and also their cost of production. A. armata produces large amounts of halogenated metabolites ( &lt 20 ??g / mg dry weight) that are sequestered in gland cells, as was demonstrated with light, epifluorescence and transmission electron microscopy. Cellular structures were identified that likely assist the release of metabolites from the gland cells to the algal surface. The halogenated metabolites of A. armata have multiple ecological roles, functioning as both inhibitors of bacterial fouling and as herbivore deterrents. Their activity against bacteria and herbivores was measured by a novel test in which the metabolites were manipulated in A. armata by omitting bromide ions from the culture media. This technique prevented the production of halogenated metabolites, but did not impact on other aspects of algal biology. Algae lacking halogenated metabolites (bromide [-] algae) had higher densities of epiphytic bacteria than those that continued to produce metabolites (bromide [+] algae). Bioassays with pure compounds against individual bacterial isolates further supported an inhibitory role for the halogenated metabolites against epiphytic bacteria, and also indicated an affect on bacterial community structure as well as abundance. Bromide (+) A. armata produced halogenated metabolites that also deterred feeding by two herbivores (an amphipod and an abalone), but not a third (an opisthobranch mollusc). A novel outcome from these feeding assays was the demonstration of a relationship between herbivore size and consumption of the chemically defended A. armata by the abalone Haliotis rubra. In addition to the fitness benefits gained from chemical defence, there were also costs for allocating resources to secondary metabolites. These costs were only detected under limiting light resources, consistent with predictions of the plant defence models. The integration of chemical analyses and cellular measures of chemical defence proved essential in elucidating resource allocation to chemical defence in the filamentous stage of A. armata. This thesis highlights that the simple relationships between growth and defence in filamentous algae can provide an excellent model for studies of the ecology and evolution of chemical defences in marine algae.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 45-54). Also available on the World Wide Web.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

I investigated the ecological functions of halogenated secondary metabolites from the red alga Asparagopsis armata, their localisation in specialised cells and also their cost of production. A. armata produces large amounts of halogenated metabolites ( &lt 20 ??g / mg dry weight) that are sequestered in gland cells, as was demonstrated with light, epifluorescence and transmission electron microscopy. Cellular structures were identified that likely assist the release of metabolites from the gland cells to the algal surface. The halogenated metabolites of A. armata have multiple ecological roles, functioning as both inhibitors of bacterial fouling and as herbivore deterrents. Their activity against bacteria and herbivores was measured by a novel test in which the metabolites were manipulated in A. armata by omitting bromide ions from the culture media. This technique prevented the production of halogenated metabolites, but did not impact on other aspects of algal biology. Algae lacking halogenated metabolites (bromide [-] algae) had higher densities of epiphytic bacteria than those that continued to produce metabolites (bromide [+] algae). Bioassays with pure compounds against individual bacterial isolates further supported an inhibitory role for the halogenated metabolites against epiphytic bacteria, and also indicated an affect on bacterial community structure as well as abundance. Bromide (+) A. armata produced halogenated metabolites that also deterred feeding by two herbivores (an amphipod and an abalone), but not a third (an opisthobranch mollusc). A novel outcome from these feeding assays was the demonstration of a relationship between herbivore size and consumption of the chemically defended A. armata by the abalone Haliotis rubra. In addition to the fitness benefits gained from chemical defence, there were also costs for allocating resources to secondary metabolites. These costs were only detected under limiting light resources, consistent with predictions of the plant defence models. The integration of chemical analyses and cellular measures of chemical defence proved essential in elucidating resource allocation to chemical defence in the filamentous stage of A. armata. This thesis highlights that the simple relationships between growth and defence in filamentous algae can provide an excellent model for studies of the ecology and evolution of chemical defences in marine algae.

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references (p. 223-227).

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

The Sargassum community consists of a unique and idverse assemblage of fauna critical to pelagic food chains. Associated organisms presumably have adaptations to assist in finding Sargassum. This study investigated cues used for habitat location and selection by the Sargassum crab, Portunus sayi. Chemical detection trials were conducted with a two-chamber choice apparatus with Sargassum spp. and Thalassia testudinum as source odors. Visual detection trials (devoid of chemical cues) and habitat selection trials were conducted in which crabs were given a choice of habitats. Results showed that P. sayi respoded to chemical odors from Sargassum spp. Crabs visually located habitats but did not visually distinguish between different habitats. In habitat selection trials, crabs selected Sargassum spp. over artificial Sargassum and T. testudinum. These results suggest that crabs isolated from Sargassum likely use chemoreception from longer distances ; within visual proximity of a potential patch, crabs use both chemical and visual information. / by Lorin E. West. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

The ecosystem created by pelagic Sargassum is important in the life histories of a number of economically and ecologically important associated organisms. Fishes play a vital role in this food web and nutrient flow within these systems, but it is unknown how they locate these floating habitats. This study examined the role of natural chemical cues from Sargassum patches and the synthetic chemical Dimethylsulfonionpropionate (DMSP) for an associated fish, the planehead filefish (Stephanolepis hispidus) and a control fish species not associated with Sargassum, the masked goby (Coryphopterus personatus). Choice trials with a Y-maze apparatus determined that S. hispidus responded significantly to chemical cues from Sargassum while C. personatus did not. DMSP cues did not result in any significant behavioral responses for either fish. Demonstrating that S. hispidus can respond to chemical cues from Sargassum helps further our understanding of this unique floating algal reef and how fishes may locate it. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Coral diseases have become more prevalent and destructive over the past 20 years, possibly due to an increase in stressful environmental factors that may weaken corals defenses against disease. Aspergillosis is a disease caused by the fungus Aspergillus sydowii, which apparently infects only two species of gorgonian corals in the Caribbean Ocean (Gorgonia ventalina and G. flabellum). We hypothesized that the differential resistance to infection is caused by differences in chemical defenses among gorgonians. Freeze-dried gorgonian powders and extracts deterred fungal growth, but potencies varied among gorgonian species and among fungi. Extracts and powders generated from G. ventalina all strongly inhibited fungal growth. Since G. ventalina was predicted to have weak antifungal chemical defenses compared to gorgonians not known to suffer from aspergillosis, we concluded that gorgonian susceptibility to fungal infection is determined by factors other than, or in addition to, chemical defenses. In order to investigate specific gorgonian antifungal strategies, we attempted to use bioassay-guided fractionation to isolate antifungal compounds from four gorgonians: Gorgonia ventalina, Briareum asbestinum, Eunicea succinea, and Pseudopterogorgia americana. We succeeded in isolating two antifungal compounds, diastereomers of 9,11-seco-24-hydroxydinosterol, from the gorgonian Pseudopterogorgia americana. This compound was previously identified by other groups, but this study is the first to establish its antifungal activity. At natural concentration, one diastereomer of 9,11-seco-24-hydroxydinosterol inhibited the growth of three different fungi, suggesting that at least this diastereomer may possess broad-spectrum antifungal activity. The results from our survey of gorgonian chemical defenses indicate that susceptibility to aspergillosis cannot be explained by chemical growth inhibition alone. Further areas of investigation include induction of gorgonian chemical defenses, examination of growth-inhibiting mechanisms of antifungal metabolites, and identification of non-chemical factors affecting gorgonians vulnerability to fungal infection.

Thesis (Ph.D.)--Victoria University of Wellington, 2008. / Includes bibliographical references.