Graduate Thesis Or Dissertation
 

Diel changes in marine neuston and plankton communities of Sequim Bay, Washington

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763954b

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  • Studies of the diel behavior of phytoplankton are numerous, however, little work has been done on diel changes in neuston, the organisms inhabiting the surface microlayer. Sampling of the neuston and plankton of Sequim Bay, Washington was conducted on 18-19 August 1983 at four hour intervals. Neuston samples (upper 50 um) were collected using a recently developed glass plate collector. Plankton from 0.4 m and 1.5 m was collected in submerged polyethylene bottles. Samples were analyzed spectrophotometricaliy for photosynthetic pigment concentrations (chlorophylls a, b, c, total carotene and phaeopigments). The presence and density of each taxon of microalga was enumerated microscopically. The neuston community exhibited greater densities and lower species diversities (1 - Simpson's Diversity Index) than did the plankton community. Nocturnal decreases of species diversity were observed in microlayer samples whereas diversity remained relatively constant at 0.4 m and 1.5 m. Several species, Ceratium furca, Peridinium brevipes, and Prorocentrum micans demonstrated diel patterns of increased mid-day densities in the microlayer. All photosynthetic pigment concentrations (mg pigments m⁻³ seawater) were depleted in microlayer samples and concentrations increased with depth. Chlorophyll a per individual was lowest in the microlayer and highest at 1.5 m depth. Carotene : chl a ratios were highest in the microlayer and lowest at 1.5 m depth. Changes observed in the surface microlayer over the sampling period appeared to be independent of the tidal cycle. However, changes at 0.4 m and 1.5 m depth were directly affected by the tidal changes. A "red-tide" dinoflagellate bloom persisted during the course of this study. Therefore, this data is indicative of changes occurring during a short-term, sporadic environmental condition in Sequim Bay, Washington. Further studies of much longer duration are needed to characterize diel trends in general.
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