Robert F. Whitehead

Characterization of CDOM in an organic rich river and surrounding coastal ocean in the South Atlantic Bight

Abstract.Variability in chromophoric dissolved organic carbon (CDOM) was characterized in and around the Cape Fear River and Onslow Bay, North Carolina USA. The river end member of the study is extremely rich in CDOM, thus the Cape Fear River serves as a point source of CDOM-rich water into the southeastern Atlantic bight. The river plume is easily traceable and generally extends in a southwesterly direction along the coastline into Long Bay. Depending on physical processes and river flow, the plume can meander somewhat and may even turn northward for short periods of time. The oceanic end member of this study was the Gulf Stream. Samples from the Gulf Stream were obtained up to 97 km off shore. The experimental approach focused on the qualitative and quantitative description of CDOM from fresh-to-oceanic waters. CDOM was characterized by excitation emission matrix (EEM) fluorescence and UV/VIS spectroscopy. Variability of CDOM absorption in the relatively small area of the Cape Fear River estuary and surrounding coastal ocean was very high. The observed range of variability of CDOM absorption coefficient, aCDOM(350), extended over nearly the entire range of CDOM absorption in the literature: 0.046 = aCDOM(350) = 29.9 m–1. Changes in CDOM absorption spectrum slope coefficient S, were small in the Cape Fear River plume area, but relatively large in Onslow Bay. CDOM EEM spectra indicated that a radical change in composition of CDOM occurs along the river-to-oceanic salinity gradient. CDOM in the coastal ocean was characterized by strong reduction of the three principal intensity peaks: A, C, and M, and a prominent contribution of the T peak to the fluorescence spectrum. The fluorescence intensity is linearly related with absorption. There is a strong inverse relationship between salinity and CDOM absorption. The distribution of the slope coefficient and the percent contribution of respective peak intensities to the total EEM intensity showed that CDOM undergoes conservative mixing until it approached oceanic salinity. Thus, CDOM is so concentrated in the river that mixing and other physical processes mask photochemical or biological alteration of its composition.

Macroalgae Has No Effect on the Severity and Dynamics of Caribbean Yellow Band Disease

By removing herbivores and promoting increases in macroalgae, overfishing is thought to indirectly cause coral disease and mortality. We performed three field manipulations to test the general hypothesis that overfishing and the subsequent alteration of coral reef trophic dynamics are a cause of coral epizootics. Specifically, we asked whether the presence of macroalgae can influence within- and among-colony spread rates of Caribbean Yellow Band Disease in Montastraea faveolata. Macroalgae were placed next to infected and healthy, adult and small coral colonies to measure effects on disease spread rate, coral growth and coral survival. Surprisingly, the addition of macroalgae did not affect disease severity or coral fitness. Our results indicate that macroalgae have no effect on the severity and dynamics of Caribbean Yellow Band Disease and that fisheries management alone will not mitigate the effects of this important epizootic.

CO2 enrichment and reduced seawater pH had no effect on the embryonic development of Acropora palmata (Anthozoa, Scleractinia).

The effects of decreased pH, caused by carbon dioxide (CO2) dissolution in seawater (known as ocean acidification (OA)), on the development of newly fertilized eggs of the Caribbean reef-building coral, Acropora palmata, was tested in three experiments conducted during the summers of 2008 and 2009 (two repeats). Three levels of CO2 enrichment were used: present day conditions (400 µatm, pH 8.1) and two CO2-enriched conditions (700 µatm, pH 7.9, and 1000 µatm, pH 7.7). No effects on the progression or timing of development, or embryo and larval size, were detected in any of the three experimental runs. The results show that the embryos and larvae of A. palmata are able to develop normally under seawater pH of at least 0.4 pH units lower than the present levels. Acropora palmata larvae do not usually begin to calcify after settlement, so this study only examined the non-calcifying part of the life cycle of this species. Most of the concern about the effects of OA on marine organisms centers on its effect on calcification. Negative effects of OA on the embryonic development of this species were not found and they may not manifest until the newly settled polyps begin to calcify.

CISME: A self-contained diver portable metabolism and energetics system

This paper describes a self-contained diver-portable instrument designed to non-destructively measure coral respiration and photosynthesis in situ. In situ instruments are needed to promote rapid assessment and monitoring of metabolic health of corals and other benthic organisms affected by ocean acidification, global warming, and other stressors, both anthropogenic and natural. Non-destructive tools are especially needed for reef corals because their live cover is greatly reduced and destructive sampling in many locations is prohibited. University of North Carolina Wilmington and Physical Sciences Inc., under the auspices of the NOAA-funded Cooperative Institute for Ocean Exploration, Research and Technology, have designed, fabricated and field tested such an instrument. CISME (Coral in Situ Metabolism and Energetics) is a compact instrument that measures dissolved oxygen, pH and temperature, which can then be used to determine respiration and photosynthesis rates of corals and a variety of other marine organisms. CISME has a sample port for introducing reagents (e.g. CO2 enriched seawater) or withdrawing water samples for analyses that require laboratory instrumentation (e.g. total alkalinity for calcification rates). The instrument has a broad spectrum light array capable of mimicking natural light intensities during photosynthetic measurements. Laboratory and field tests demonstrate that the instrument produces quick, consistent metabolic measurements, as well as photosynthesis vs. irradiance response curves. These features make CISME suitable for experiments with pollutants and for ocean acidification research. The new technology will provide a new field tool for assessing coral reef ecosystem health.

Modeling the effect of ozone loss on photobleaching of chromophoric dissolved organic matter in the St. Lawrence estuary

Temporal trends in total ozone for the St. Lawrence estuary were estimated from ground-based measurements at the NOAA/CMDL station in Caribou, Maine. Linear regression analysis showed that from 1979 to 1999 total ozone has decreased by about 3.3% per decade on an annual basis and ≤6.2% per decade on a monthly basis relative to unperturbed (pre-CFC) levels. The influence of increased ultraviolet-B (280–320 nm) radiation associated with ozone depletion on water column photochemical processes was evaluated by modeling the photobleaching of chromophoric dissolved organic material (CDOM). Linear regression analysis showed small (<0.5% per decade), but statistically significant upward trends in maximum noontime photobleaching rates. Most notably, positive trends in relative rates for May, June, and July, when maximum absolute rates are expected, were predicted. A global model based on TOMS ozone data revealed increases in photobleaching of ≤3% per decade at high latitudes in the Southern Hemisphere. Radiation amplification factors for increases in photochemically weighted UV (280–400 nm) in response to ozone depletion were estimated at 0.1 and 0.08 for photobleaching of CDOM absorbance at 300 and 350 nm, respectively. Application of the laboratory-based model to conditions that more closely resembled those in situ were variable with both overestimation and underestimation of measured rates. The differences between modeled rates and observed rates under quasi-natural conditions were as large or larger than the predicted increases due to ozone depletion. These comparisons suggest that biological activity and mixing play an important, but as yet ill-defined, role in modifying photochemical processes.