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The near-bottom chlorophyll A maximum in Onslow Bay : effects of wave events on benthic microalgae resuspension

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Gianluca Manes (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Daniel Baden

Abstract: Both a significant benthic microflora and a near-bottom chlorophyll a maximum are present in Onslow Bay, NC. Over 80% of the chlorophyll a is associated with the sediments, supporting previous findings that primary production by microalgae on the continental shelf out to the shelf break is important. Benthic microalgae are likely to be the major producers in continental shelves like Onslow Bay where light flux to the bottom appears to be adequate to support them. The existence of a near-bottom chlorophyll a maximum is due partly to resuspension by surface gravity waves. Orbital velocities and bottom shear stresses exceeded thresholds of 0.2-0.3 m/s and 0.2 N/m2, respectively, and caused statistically significant increases in turbidity (NTU) and fluorescence (RFU). In addition to the magnitude of the orbital velocity measured by Turner SCUFA II in situ loggers the change in orbital velocity (or bottom shear stress) before and after a storm event, and the duration of the event also control the resuspension phenomena. However, other processes such as in situ growth of near-bottom microflora, sinking, and the spring bloom have to be considered as well in studying formation of near-bottom chlorophyll maxima. I observed anomalously high values of turbidity and fluorescence at 1 m from the bottom in May-June 2002 and the lowest concentration of phytoplankton in the water column (near-bottom, mid-depth, surface) during this event. I hypothesize that demersal zooplankton moved into the water column at night and reentered the substrate by day and that holozooplankton were down in the water column near the bottom during the day and migrated upward at night. These migration patterns were responsible for the fluorescence and turbidity pattern. The high spikes in turbidity signals at 1 m were probably produced by the high density of zooplankton (~10 4m-2) and the fluorescence signal at 1 m was the result of their nocturnal feeding (the fluorescence signal was related to the chlorophyll a content in their guts).

Additional Information

A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Biotic communities--North Carolina--Onslow Bay, Chlorophyll--North Carolina--Onslow Bay, Primary productivity (Biology)--Measurement
Biotic communities -- North Carolina -- Onslow Bay
Chlorophyll -- North Carolina -- Onslow Bay
Primary productivity (Biology) -- Measurement