Field and laboratory studies on the effects of the Texas brown tide alga Aureoumbra lagunensis on the copepod Acartia tonsa /
Blooms of Aureoumbra lagunensis, a small phytoplankton species known as the Texas brown tide alga, occurred extensively throughout the Laguna Madre from 1990 to 1997, and high concentrations of this alga can still be found there, especially during the summer. However, the reasons for the prominence...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=727852801&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Blooms of Aureoumbra lagunensis, a small phytoplankton species known as the Texas brown tide alga, occurred extensively throughout the Laguna Madre from 1990 to 1997, and high concentrations of this alga can still be found there, especially during the summer. However, the reasons for the prominence and persistence of this species in Laguna Madre are largely unknown. Before the onset of the brown tide, Acartia tonsa was the most abundant mesozooplankter in Laguna Madre, but its population, egg production and grazing rates declined during bloom years. To assess the effects of A.lagunensis on A. tonsa, series of field studies were carried out in Corpus Christi Bay (CCB) and Baffin Bay (BFB) between July 1997 and July 1998, in which the density, size, length, condition factor of A. tonsa and grazing impacts of A.tonsa on natural phytoplankton and microzooplankton were measured. The digestibility and viability of A. lagunensis after gut passage was tested in the laboratory and the nutritional condition of A. tonsa was assessed using RNA:DNA ratios for field and laboratory samples. Principal results are: 1.) In general A. tonsa females in BFB were smaller and had lower values of dry weight than individuals in CCB, but they exhibited a higher weight relative to their size and thus had higher values of condition factor. 2.) Higher clearance rates for chlorophyll-a size fractions > 10 æm were observed in field feeding experiments, suggesting that copepods could favour A. lagunensis population growth by removing other algal competitors. 3.) RNA:DNA ratios clearly demonstrate the negative effects of feeding on A. lagunensis, since RNA:DNA ratios of copepods fed this species were low and indicative of very poor nutritional condition. 4.) Undigested cells of A. lagunensis were found in the fecal pellets of A. tonsa and some of them were still viable after gut passage. The ability of A. lagunensis to partially resist digestion could perhaps represent an important adaptation against grazers, and thereby enable populations to be maintained in an otherwise top-down controlled ecosystem. |
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| Item Description: | Vita. "Major Subject: Oceanography". |
| Physical Description: | xiii, 120 leaves : illustrations, map ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 112-118). |