Browsing by Author "Walsh, S"

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    Benthic foraminiferal assemblages from Kiritimati (Christmas) Island indicate human-mediated nutrification has occurred over the scale of decades
    (Inter-Research Science Publisher, 2012-06-07) Carilli, JE; Walsh, S
    Community assemblages of live and dead benthic foraminifera from Kiritimati (Christmas) Island, Kiribati, were used to investigate changes in nutrification before and after human occupation. Benthic foraminiferal assemblages have previously been shown to have strong empirical relationships with water quality: mixotrophic, symbiont-bearing foraminifera dominate in clear, nutrient-poor waters, while heterotrophic and/or opportunistic foraminifera are more prevalent in polluted or nutrified waters. After human occupation, the proportion of mixotrophic taxa decreased significantly at all sites on Kiritimati with the largest decreases observed at sites with the highest fishing pressure. These changes in the benthic foraminiferal assemblage indicate that nutrification has occurred on Kiritimati over the scale of decades, possibly due to changes in trophic structure and nutrient cycling caused by fishing. © 2012, Inter-Research.
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    Century-scale records of coral growth rates indicate that local stressors reduce coral thermal tolerance threshold
    (Wiley-Blackwell Publishing, 2010-04-01) Carilli, JE; Norris, RD; Black, B; Walsh, S; McField, M
    Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence. Using tree-ring techniques, we produced master chronologies of growth rates in the dominant reef builder, massive Montastraea faveolata corals, over the past 75-150 years from the Mesoamerican Reef. Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid-century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree-heating-months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors. © 2010, Wiley-Blackwell.