Abundance and foraging ability of physonect siphonophores in subtropical oceanic surface waters.
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| Format: | Thesis Book |
| Language: | English |
| Published: |
1982.
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| Online Access: | ProQuest, Abstract Link to OAKTrust Copy Link to ProQuest Copy |
| Abstract: | Daytime abundances of physonect and selected calycophore siphonophores were tallied during SCUBA dives in the upper 15 m of subtropical oceanic surface waters off the Bahamas and in the western Gulf of Mexico. Daytime physonect densities in Bahamian surface waters during summer 1979 averaged less than 2/25,000 m('3). In spring 1980, physonects averaged 5/25,000 m('3) in Gulf of Mexico surface waters, while in summer 1980 physonect siphonophores were rarely observed (< 1/25,000 m('3)). In fall 1980, physonects in the Gulf averaged 30/25,000 m('3) and 8/25,000 m('3) within the surface waters of a mesoscale cyclonic circulation feature and within those of an anticyclonic feature, respectively. In winter 1981 they averaged 16 and 8 per 25,000 m('3) in cyclonic and anticyclonic features, respectively. Environmental correlations with the near-surface abundance patterns are discussed. During SCUBA dives, the physonect siphonophores Forskalia tholoides and F. edwardsi were hand-collected for shipboard foraging experiments. Large volume aquaria (0.2 m('3) and 1.0 m('3)) were used to estimate the foraging ability of these predators at prey densities similar to those of oceanic surface waters (51, 113, 226, and 452 prey m('-3)). Enclosure of these gelatinous planktivores in large volume aquaria did not appear to adversely affect their feeding or swimming behavior. When feeding on oceanic copepods, the number of prey ingested was proportional to prey concentration at densities at and above 200 prey m('-3). Based on physonect numerical abundance and prey capture rate, the foraging impact of the physonect siphonophore population in the western Gulf of Mexico is discussed. Stochastic numerical models were also constructed to test the importance of prey behvior to prey encounter by tentaculate planktivores. The predator for these simulations was patterned as a Forskalia species. Prey swimming behaviors modeled were random directional movement in the X-Y plane and vertically in the Z direction, directed movement in the X-Y plane with a reduced probability of movement along the Z-axis, and "hop and sink" swimming behavior. Results of these simulations indicate thay prey behavior may contribute to the quantitative differences in the number of prey encountered by tentaculate planktivores. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Oceanography." |
| Physical Description: | xv, 205 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 157-165). |