Marine chemical ecology

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.

The unique coral reef at St. Lucie Reef (Stuart, FL) persists despite environmental variability from extensive freshwater discharges, summer upwelling, and thermal
instability. By examining the symbiotic zooxanthellae, or Symbiodinium, that reside
in corals, we can gain insight to coral physiology impacted by local stressors. Two
scleractinian corals, Montastraea cavernosa and Pseudodiploria clivosa were sampled
over 1.5 years, including both wet and dry seasons. Zooxanthellae were isolated and
quantitatively characterized using standard measurements and molecular techniques.
Both coral species varied in zooxanthellae biomass, where Pseudodiploria clivosa had
Higher cell densities and chlorophyll concentrations than Montastraea cavernosa. Over
time, these parameters varied, but were not significantly altered by fresh water discharge events. Symbiodinium diversity and abundance were identified by ITS2 region amplification and next-generation sequencing .Novel associations between Symbiodinium and each coral explained the observed physiological differences. The symbioses remained stable throughout and could indicate local adaptation for St. Lucie Reef corals.

The Sargassum community is comprised of a unique and diverse assemblage of organisms. Habitat detection by two of the most common invertebrates, Latreutes fucorum and Leander tenuicornis , was investigated. Results of this study do not support that either L. fucorum or L. tenuicornis respond to chemical cues released by the Sargassum habitat in the absence of other information. Habitat selection of both shrimp species was examined as well. Both L. fucorum and L. tenuicornis selected live Sargassum over artificial Sargassum . Moreover, L. fucorum selected Sargassum natans over Sargassum fluitans when only visual cues were available, whereas large-sized L. tenuicornis selected S. fluitans under the same conditions. Conversely, habitat selection trials combining both chemical and visual cues resulted in no preference between the two Sargassum species by either shrimp species. Additional ecological factors that possibly influence habitat location and selection are discussed as well as the importance of Sargassum in terms of pelagic fisheries management.

The marine environment has proven to be an extremely rich source of novel natural products with activities in a variety of biological assays. The field of marine natural products chemistry has enjoyed an explosion of growth over the past 40 years and currently there are marine-derived metabolites in clinical trials for cancer, analgesia, allergy and cognitive diseases. Even with this tremendous development, it is clear that chemists and pharmacologists are only beginning to scratch the surface of the biomedical potential of marine organisms. One problem with this source of new pharmaceuticals is that the supply of such compounds can be problematic. The thesis describes projects directed at fundamental biosynthetic questions regarding terpenes from marine corals. In a general sense, these projects are directed as addressing the supply issue identified above. One project examined the origin of terpene building blocks in the coral Pseudopterogorgia elisabethae. A second project focused on the characterization of terpenes from Leptogorgia minimata. Here, a new cembranoid diterpene was isolated. Experiments were also conducted to identify a microbial source of terpene biosynthesis in this system. Data strongly supported a bacterial origin of these compounds.

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.