Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
Gray's Reef Expedition 2012
Mission Information
 

Arc Shell Collections

Conceptual View Of Benthic Fauna At GRNMS

Conceptual View Of Benthic Fauna At GRNMS
(Photo: NOAA-NCCOS)
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During the Gray's Reef cruise aboard NOAA Ship Nancy Foster, scientists will be collecting samples as part of a long-term monitoring effort to assess status of ecological condition and potential stressor impacts within the sanctuary with a focus on the soft-bottom benthos and sediment quality. The work is a follow-up to previous surveys of benthic macro-infauna (sediment-dwelling animals > 0.5 mm) and concentrations of chemical contaminants in sediments and biota conducted in 2000 and 2005. Results of these earlier studies (Cooksey et al. 2004, Hyland et al. 2006; Balthis et al. 2007) suggested that the sanctuary has been in "good health" with respect to these properties; however, trace concentrations of pesticides, PCBs, and PAHs were detected in both sediments and biota (albeit at low concentrations) demonstrating that chemicals originating from human activities are capable of reaching the offshore sanctuary environment and thus should continue to be monitored for any future problems that might emerge. The prior studies also documented highly diverse benthic assemblages living within these unconsolidated substrates. Such fauna play vital roles in the offshore ecosystem including sediment bioturbation and stabilization, detrital decomposition, nutrient cycling, and energy flow to higher trophic levels.

Station locations for 2012 surveys

Station locations for 2012 surveys
(Photo: NOAA-NCCOS)
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This summer, twelve years after the original baseline survey and seven years after the first follow-up study, scientists will provide a re-evaluation of sediment quality and condition of resident benthic fauna within the sanctuary boundaries. This will be accomplished through a combination of cruises aboard NOAA Ship Nancy Foster in May to collect mollusk (arc shell) samples for tissue-contaminant analysis and the sanctuary's vessel, R/V Joe Ferguson, in July to collect all other samples. The objective of the work is to generate a third set of data points for the long-term monitoring record as a basis for tracking status and trends in sanctuary conditions and providing support to important management products such as the GRNMS management plan (NOAA 2006) and the GRNMS Condition Report (Office of National Marine Sanctuaries, 2008).

Benthic Grab Sampling

Benthic Grab Sampling
(Photo: NOAA-NCCOS)

During both the 2000 and 2005 surveys, 20 stations were sampled throughout the sanctuary boundaries. A random sampling design was applied to support probability-based estimates of the percentage of area with degraded versus non-degraded condition relative to various measured environmental indicators. The resulting sampling framework is a 58-km2 grid of 20 individual 2.9-km2 cells, each of which contains a randomly selected station, and which together are representative of the total area of the sanctuary. With such a design, each sampling point (station) is a statistically valid probability sample.

Thus, percentages of the sanctuary with degraded vs. non-degraded environmental condition relative to selected indicators and corresponding management thresholds can be estimated based on conditions observed at individual sampling points. The percentage of overall degraded area, for example, can be computed by dividing the summed areas of individual cells in which impacts were observed by the total area of the sanctuary. Statistical confidence intervals around these estimates can be calculated as well. For the upcoming 2012 survey, the same probabilistic sampling approach will be applied, with a new random station location selected within each of the 20 cells.

Sampling Parameters: Click image for larger view

Sampling Parameters
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At each of the 20 stations, samples will be collected for characterization of general habitat conditions (depth, temperature, salinity, pH, DO, TOC, grain size), concentrations of sediment contaminants (metals, pesticides, PCBs, PAHs), diversity and abundance of macro-infauna, and aesthetic quality (presence of anthropogenic debris, visible oil, noxious sediment odor, and water clarity/turbidity) (see Table). A 0.04 m2 Young grab will be used to collect sediment samples for analysis of benthic infaunal and sediment-quality variables. Water-quality variables (salinity, conductivity, dissolved oxygen, pH, and temperature) will be measured along continuous vertical profiles at each station, on both the downcast and upcast, with a Seabird 19plus CTD profiler. A Nisken bottle also will be used at each station to collect discrete samples of near-surface and near-bottom water for turbidity measurements.

Turkey Wing Arc Shell

Turkey Wing Arc Shell
(Photo:Victor Boswell

During both the 2000 and 2005 surveys, benthic/demersal species (turkey wing arc shell Arca zebra) were collected in selected areas and analyzed for chemical contaminants. Tissue concentrations were below human-health guidelines. However, similar to results for sediments, tissues of both species contained trace concentrations of additional chemical contaminants associated with human sources (pesticides, PCBs, PAHs). These same species will be targeted again for the 2012 effort. Divers will attempt to collect A. zebra samples during the NOAA Ship Nancy Foster cruise in May.

Resulting data from the new 2012 study will be compared to earlier data from 2000 and 2005 to look for trends in the measured variables and any evidence of changes in the quality of the sanctuary condition including potential signals of anthropogenic stress. The information should help fulfill important science and management goals of the sanctuary including providing valuable support to future management plans and condition reports.

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