Date Awarded

2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Mark R. Patterson

Abstract

Water-flow is a vital component to the life histories of sessile marine invertebrates and essential to the structure and function of coral reefs. Recent studies have identified water-flow as an asset in the resistance to and recovery from short-term bleaching events of high irradiance and thermal increases. to determine whether the benefits of water-flow scale from the landscape level down to the flow patterns experienced over individual polyps and to quantify potential metabolic consequences, three studies were performed on Montastrea annularis (Ellis and Solander, 1786), using in situ heated bleaching flow-chambers during two saturation missions at the Aquarius underwater laboratory. The first study developed a single coral polyp sampling method and a low-volume protein extraction and quantification protocol. The second study determined and quantified position-effects (upstream and downstream) of enhanced water-flow rates on the organism's photobiology, expressed as Quantum Yield (QY), and within the same experimental set-up, a third study used the regulation and synthesis of the heat shock proteins 70 and 90 (hsp70 and hsp90) as biomarkers, thus allowing the quantification of potential affects of asymmetric flow pattern across the same six coral colonies. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis were used to resolve as little as 87 pg of hsp70 per coral polyp. Relatively large amounts of total protein (x?»= 77 SD +/- 9 mug) were recoverable from single coral polyps. Montastrea annularis colonies developed and sustained significant spatially asymmetric patterns of QY across the entire coral surface, with the upstream side of the colonies exhibiting reduced QY. The mechanism producing this pattern is also unclear. We speculate that increased flow may lead to an up-regulation of photosynthesis by the entire colony through bicarbonate delivery accentuated by the Q10 effect. Local down-regulation of the photosynthetic response (decreased quantum yield) might then occur to keep tissue oxygen concentrations within tolerable limits. The same colonies also developed and sustained significant spatially asymmetric patterns of stress protein synthesis across the entire coral surface, with upstream sectors expressing more hsp70. The mechanism producing this pattern is unclear. We speculate that increased flow may lead to an initial up-regulation in the synthesis of hsps by the entire colony followed by a down-regulation in discrete areas of increased hydraulic stress or biochemical energy requirements. This study is the first to investigate asymmetric patterns of flow-modulated stress protein synthesis and photosynthetic regulation, within mounding and flat plate morphologies of M. annularis, during and following thermal stress and elevated water-flow. Evidence now exists that following sustained periods of increased flow, irradiance and thermal stress, a yet-to-be determined physiological threshold, if breached, can disrupt metabolic processes e.g., the regulation of molecular chaperons synthesis and/or regulate photosynthetic efficiency. Therefore we propose the existence of a water flow threshold (FTmax) that operates in concert with e.g. , temperature. The threshold is proposed to occur somewhere within the range of 3.0--45.0 cm s-1. Flow appears not only to accelerate the effects of the co-stressor temperature, but regulates through the direct effects of velocity, exactly where on the coral regulation of stress protein synthesis and photosynthetic efficiency occurs. Water flow might now be likened to an agent provocateur and posited to join the ranks of other bleaching conspirators such as solar radiation and oxygen toxicity, which act synergistically with temperature in lowering the threshold at which thermal anomalies stimulate coral stress.

DOI

https://dx.doi.org/doi:10.25773/v5-nna9-tw34

Rights

© The Author

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