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Environmental surveys reveal diversity in free-living populations of Symbiodinium from Caribbean and Pacific reefs

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Title: Environmental surveys reveal diversity in free-living populations of Symbiodinium from Caribbean and Pacific reefs
Authors: Manning, Mackenzie Marie
Keywords: Dinoflagellates -- Caribbean Sea
Dinoflagellates -- Pacific Ocean
Coral reef ecology -- Caribbean Sea
Coral reef ecology -- Pacific Ocean
Issue Date: 2006
Abstract: The Symbiodinium species complex is genetically and ecologically diverse. Small and large-scale biogeographic distribution patterns reveal that some symbiont types are host specific while others are compatible with a wide range of hosts (Baker and Rowan 1997; LaJeunesse 2002; LaJeunesse et al. 2004; Ulstrup and van Oppen 2003). Observations of natural bleaching patterns, coral-algal associations under different stress regimes, cultured symbionts under different environmental conditions, and symbiont infectivity studies have led investigators to believe that different host-symbiont combinations are possible and can exhibit different tolerances to stress (Baker 200 I; Berkelmans and van Oppen 2006; Glynn 1993; Hoegh-Guldberg and Smith 1989; Hoegh-Guldberg and Fine 2004; Kinzie et al. 2001; Kirk et al. 2005; Robison and Warner 2006; Rodriguez-Lanetty et al. 2004; Rowan et al. 1997). These observations lead to the formulation of the Adaptive Bleaching Hypothesis (ABH), first described by Buddemeier and Fautin (1993). The ABH posits that coral bleaching provides an opportunity for corals to modify their symbiotic communities in response to changing environmental conditions. In this light, bleaching is a way for corals to adapt to such change within an ecologically relevant time scale. This could theoretically be achieved by two mechanisms that are not mutually exclusive. The first mechanism facilitates an exchange of the current, less physiologically tolerant symbiont community for a new community of symbionts acquired from environmental pools that are physiologically better suited to the prevailing conditions ('switching'). The second mechanism results in a rearrangement of the abundance of different types of symbionts already present within the host coral ('shuffling'). There are a number of critical assumptions that must be met in order to accept this hypothesis: I) that multiple types of symbiotic algae exist in nature, 2) that different types of symbionts are characterized by different physiological optima, 3) that corals with new symbiont types exhibit higher resilience in the face of further environmental change, and 4) that a diversity of symbiont types are available and free-living in the environment (i.e. water column and substrates) and can colonize bleached hosts. While the first three assumptions have, or are currently being explored in some detail (see Baker 2001; Kinzie et al. 2001; Savage et al. 2002; LaJeunesse 2004), research regarding the last assumption has been gradual. There is currently very little data on the diversity, spatial distribution, and temporal behavior of Symbiodinium populations free-living in the environment (Kinzie et al. 200 I). Research utilizing experimentally bleached, facultative hosts and aposymbiotic larvae (without symbionts) has shown infection by Symbiodinium when exposed to environmental seawater (Kinzie et al. 2001; Lewis and Coffroth 2004; Thornhill et al. 2006). There are two reports of free-living Symbiodinium being cultured from waters and/or sediments surrounding potential hosts (Carlos et al. 1999; Gou et al. 2003). As new discoveries concerning the ecology, physiology and fitness of the symbiosis are being made, it is becoming increasingly important to fully characterize the availability and diversity of environmental pools of free-living Symbiodinium. We have developed a protocol to explore the diversity of free-living Symbiodinium in seawater and have used it to analyze samples taken from coastal, tropical reef habitats in the Pacific and Caribbean. Using two different molecular markers, one specific to Symbiodinium, we have successfully resolved known Symbiodinium types in these seawater samples, including C3, C15, B1, and D1. We report a number of novel sequence types that have not previously been described. Our results demonstrate the effectiveness of this protocol in examining Symbiodinium diversity across spatial scales and we hope that the broad application of this protocol will provide insight in the temporal and spatial variability and environmental resilience of free-living Symbiodinium populations.
Description: Thesis (M.S.)--University of Hawaii at Manoa, 2006.
Includes bibliographical references (leaves 32-38).
v, 38 leaves, bound 29 cm
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections:M.S. - Zoology (Marine Biology)

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