Browsing by Subject "Coral"
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Item Coral Isotope Record of Environmental Change in the Northwest Gulf of Mexico(2013-08-30) Miner, AdrianVariations in the density banding and chemical composition of the skeletal material of long-lived corals in the Gulf of Mexico preserve records of past environmental conditions. To better interpret these records, the controlling mechanisms governing carbon and oxygen isotopes in coral skeletal material must be well understood. We have studied a Montastrea faveolata coral core from the Flower Garden Banks deposited over the 161 year period from 1844 to 2005. Annual growth bands revealed by X-radiography indicate the years and rates at which this material was deposited. We used a micro-milling device to obtain calcium carbonate samples at increments corresponding to approximately monthly resolution, and measured their stable oxygen (?18O) and carbon isotope (?13C) ratios with a mass spectrometer. The stable isotope records from this Montastrea faveolata coral reflect differences in the environmental controls of ?18O and ?13C fractionation. Annual variations of ?^(18)O coincide with density bands and reflect changes of seawater temperature, which in turn are linked to climate. Annual variations of ?^(13)C, which are largely controlled by photosynthesis, coincide with changes of insolation. Changes in the annual cycle of ?^(18)O lag those of ?^(13)C by about 2 months. We propose this difference exists because at the Flower Garden Banks the response of photosynthesis to seasonal changes in insolation occurs more rapidly than that of seawater temperature. Over the 161 year period of the record, the overall trend of ?^(13)C is toward more negative values and the annual range of ?^(13)C values increases. These patterns are consistent with the flux of fossil-fuel-derived carbon dioxide from the atmosphere to the ocean. Within the period of about 1900 to 1920, several years display particularly negative values. We speculate these values may result from Northern Hemisphere volcanism and/or interannual climate fluctuations.Item Epifaunal Assemblages on Deep-water Corals in Roatan, Honduras(2012-10-30) Lavelle, KatherineDeep-water corals provide complex habitat structure for diverse assemblages of invertebrates and fishes. Similar to shallow coral reefs, oyster reefs, and seagrass beds, these complex biogenic structures serve many ecosystem functions: (a) as prey items; (b) sites for reproduction; (c) feeding stations, elevating suspension feeders above the benthos; and (d) refuges from predation. Because deep-sea corals provide some of the only three-dimensional habitats in the deep-sea, they may host distinct assemblages of epifauna. Non-destructive video surveys of deep-water coral assemblages were made to depths of 700 m at eight sites off Roatan, Honduras in May and December, 2011. Abundance, species richness, and distribution of epifauna were measured for 305 corals. We observed sixteen morphospecies of coral and twenty-six morphospecies of epifauna. Coral and epifaunal abundances were highest in the 335-449 m depth zone. Some epifauna had high fidelity for a single coral species or for a few species of similar morphological complexity. Other coral species had overlapping assemblages of habitat generalists. This is the first research on the biodiversity of deep-sea coral communities in Roatan, Honduras, and provides information on the assemblages, their depth distributions and ecological interactions.Item Investigating local adaptation in a reef-building coral(2014-08) Kenkel, Carly Danielle; Matz, Mikhail V.Environmental variation is ubiquitous in natural systems. The genetic and physiological mechanisms governing population-level responses to this variation will impact the process of speciation and the capacity for populations to persist in a changing climate. Until recently, population-level responses to environmental selection remained largely unexplored in marine systems due to the historical assumption that the inherently dispersive nature of most marine taxa would preclude their ability to specialize to local environments. This dissertation represents the first investigation of population-level responses to environmental variation in a Caribbean reef-building coral. This research integrates ecological, physiological, genetic and genomic methods to (1) determine patterns of local adaptation in the Florida Keys, (2) identify stressors driving adaptive responses, (3) distinguish the physiological and genetic mechanisms underlying coral adaptation and (4) assess the potential for future adaptation in the common reef-building coral Porites astreoides. Results demonstrate that corals adapt and/or acclimatize to their local habitat and that this specialization incurs fitness costs. Temperature differences between reefs likely play a selective role in differentiating inshore and offshore coral populations. Genetic and gene expression differences indicate that coral hosts play a substantial role in driving these population-level differences. Inshore corals exhibit greater gene expression plasticity, which may be involved in stabilizing physiological responses to temperature fluctuations experienced at inshore reefs. In addition, naïve juvenile coral recruits from inshore reefs exhibit a growth rate advantage over offshore recruits under elevated temperature treatment, suggesting that thermotolerance differences observed in adult populations could continue to evolve in response to climate change. Taken together these results provide novel insight into the drivers of reef decline in the Florida Keys and the role of the host in coral adaptation capacity.Item Understanding coral dispersal(2014-05) Davies, Sarah Whitney; Matz, Mikhail V.Understanding the factors influencing species ranges and dispersal are becoming increasingly important as climate change alters species distributions worldwide. If species are to persist, life-history strategies must rapidly evolve to accommodate shifting environments. This dissertation assesses the factors modulating dispersal in corals. First, I examined if there were any systematic differences in settlement between Indo-Pacific and Caribbean coral larvae that might explain Caribbean recruitment failures. No differences were observed, however I detected significant divergences in settlement cue preferences among coral species across both the Caribbean (Diploria strigosa, and Montastraea franksi) and the Indo-Pacific (Acropora tenuis, A. millepora, and Favia lizardensis), even for coral larvae from the same reef. Secondly, I established the extent of coral dispersal between remote reefs. I evaluated the genetic diversity and divergence across Micronesia for two coral species and investigated if these islands served as a connectivity corridor between the Indo-West-Pacific (Coral Triangle) and the Central Pacific. I found isolation-by-distance patterns whose strength depended on species, suggesting these corals are not panmictic across their ranges and that island stepping-stones facilitate gene flow to remote Pacific reefs. Next, I investigated genetic structure of symbionts in these same corals, to see if horizontally transmitted symbionts are less dispersive than their coral hosts. Symbiont genetic divergence between islands was an order of magnitude larger than host divergence and both host species and environment modulated symbiont composition. These results suggest that symbiont populations are host-specific and associating with local symbionts might be a mechanism for broadly dispersing corals to adapt locally. Lastly, I estimated heritable variation in dispersal-related traits in coral larvae. I observed strong heritable variation in gene expression, as well as parental effects on two phenotypic traits, settlement and fluorescence. I observed that patterns of differential expression in three-day-old larvae predicted variation in settlement and fluorescence two days later. Correlations between proteoglycan expression and settlement suggest that the larval extracellular matrix plays a role in settlement. Down-regulation of ribosomal proteins and differential expression of oxidative stress genes correlated with increasing fluorescence, possibly indicating reduced growth and increased stress. Overall, this dissertation contributes to our knowledge of factors affecting coral dispersal and the potential for evolution of dispersal-related traits.