Multiple Stressor Effects on Coral Physiology and Biogeochemistry PDF Download

Author: Kerri L. Dobson
Publisher:
ISBN:
Category : Coral reef biology
Languages : en
Pages : 0

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Book Description
Increases in atmospheric CO2 are causing the planet to warm. As such, corals are living closer to their upper thermal tolerance limits, leading to decreased coral health and increased mortality. Increasing sea surface temperatures alter the symbiotic relationship between the coral host and endosymbiotic algae, causing coral bleaching. Such mass bleaching events are predicted to increase in frequency and severity over the next few decades. To protect at least 50% of coral reefs, warming would have to be limited to no more than 1.2°C. Thus, global warming presents an immediate threat to coral reefs. The continuing release of anthropogenic CO2 is also leading to ocean acidification (OA): the net dissolution of atmospheric CO2 into the surface ocean leading to decreases in seawater pH, net increases in total dissolved inorganic carbon and bicarbonate species, and a net decrease in carbonate species. OA is known to cause decreases in calcification in some, but not all corals, and can also be dose-dependent. Thus, the increasing temperature and OA in the ocean co-occur. While OA can exacerbate the negative effects of temperature stress on the physiological responses of some coral species, but not others, it is unknown if OA will impede or slow coral recovery from bleaching. Previous studies have shown that coral feeding on zooplankton may serve to mitigate bleaching or OA stress and enhance recovery from such events in some species. Corals acquire fixed carbon (i.e. food) and nutrients in three ways: 1) via photosynthetically fixed carbon translocated to the coral host from the endosymbiotic algae, 2) uptake of dissolved organic carbon by the coral animal’s polyps, and 3) active eating of zooplankton and particulate organic matter by the coral polyps. While photosynthetically derived fixed carbon is critical to maintaining daily metabolism and calcification, heterotrophically derived food is critical for building lipid reserves and tissue growth. It is unknown if heterotrophy could help recovery from bleaching while also under OA conditions, or whether the thermal and pH history of corals may lay the foundation for coral capacity to acclimate to future ocean conditions. In addition, continued coastal development is leading to decreases in coastal water clarity (i.e. the amount of light penetrating the surface) and increases in nutrient concentrations due to anthropogenic run-off. Evidence suggests that modest increases in any one of temperature, nutrients, or light alone is typically beneficial to coral health, while dramatic increases in any one of these variables can have detrimental effects. For corals in the future, moderate increases in nutrients and/or nutrition might mitigate much of the negative impact of OA on coral calcification. Therefore, coral health is directly related to temperature, light, and nutrients acquired from seawater and zooplankton. However, it is unknown whether a slight increase in food availability and decrease in light level could act synergistically in coastal environments to protect corals from elevated temperature and OA stress and provide a refugia from future ocean conditions. Here, I study combinations of the interactive effects of temperature, ocean acidification, food availability, moderate nutrients, and light on corals through three studies to examine the following: 1) the physiological and biogeochemical responses of three coral species to predicted future coastal ocean conditions, 2) the interactive effects of ocean acidification, temperature, and moderate nutrients on coral physiology and biogeochemistry, and 3) the effect of ocean acidification and feeding on recovery rates of corals following single and annual bleaching.