Population structure and swarm formation of the cyclopoid copepod Dioithona oculata near mangrove cays |
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Authors: | Ambler JW; Ferrari FD; Fornshell JA |
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Institution: | 1The Evergreen State College Olympia, WA 98505, USA
2Smithsonian Oceanographic Sorting Center, Museum of Natural History, Smithsonian Institution Washington, DC 20560
3Thomas Jefferson High School for Science and Technology 6560 Braddock Road, Alexandria, VA 22312, USA
Department of Oceanography, Texas A&M University College Station, TX 77843 |
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Abstract: | The cyclopoid copepod Dioithona oculata forms swarms in water>30 on deep among prop roots of red mangroves (Rhizophoramangle) which fringe protected areas of two lagoonal cays, TwinCays, Belize. During 7 of 8 months surveyed by in situ observation,swarms were present but differed in size from small cylindricalswarms (510 cm diameter) to bands extending up to 1200m Swarms were never observed at night Swarms formed at dawnwhen light intensities reached an average value of 13.82 (logioquanta cmAbstract. s1) and dispersed at dusk atsimilar intensities Swarms observed in June formed earlier anddispersed later in the day than swarms observed in January,their swarming behavior followed seasonal changes in light intensityMean dioithonan density in swarms (10 ml1) was much higherthan the mean density (0 15 ml1) of non-swarming dioithonansaround mangrove prop roots. In open water 35 m away fromthe mangroves, mean dioithonan density was 7 9 x 105ml1 during the day, and 2 68 x103 ml1 at nightSwarms were composed predominantly of adults and copepodid stagesIV and V, although younger copepodid stages could be presentNauplii were never present. The average copepodid stagefor all 95 swarms sampled was 5 3, where 6 0 represents a swarmwith only adults In open water 35 m away from the mangroves,the youngest copepodids (stage one) dominated the dioithonanpopulation during the day. At night when swarms dispersed toopen waters, average copepodid stage was higher (3 5) comparedwith the day value (1.2) in open waters. Although densitiesin swarms were higher in June than January, average copepodidstage in June was higher (5 6) than that in January (4.9). Ahigher percentage of adults were females during June than January.Therefore higher densities did not result from increases ofsmaller stages in swarms, but perhaps changes in behavior orpopulation structure. |
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