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dc.contributor.authorSilva-Serra, M. Angelica.en_US
dc.date.accessioned2014-10-21T12:37:16Z
dc.date.available2014-10-21T12:37:16Z
dc.date.issued1996en_US
dc.identifier.otherAAINN15816en_US
dc.identifier.urihttp://hdl.handle.net/10222/55105
dc.descriptionThe distribution of pelagic marine invertebrate larvae has been considered mainly to be driven by physical characteristics of the ecosystem, but there is evidence that behaviour influences vertical distribution. I examined the role of active swimming behaviours on the vertical distribution of sea scallop Placopecten magellanicus larvae by combining a series of experimental observations in microcosms and mesocosms.en_US
dc.descriptionScallop larvae showed consistent behaviours that may be responsible for their retention in areas of patchy distribution of phytoplankton, and could result in aggregations in areas of high productivity. Larval swimming throughout ontogeny consisted basically of two modes: vertically oriented helical patterns and vertical straight lines, either ascending or descending. In the helical mode, larval vertical displacement rates during ascent increased with larval age from 0.09 to 1.05 mm $s\sp{-1}$ (VVU); however, during descent displacement rates remained relatively constant with age between 0.20 and 0.37 mm $s\sp{-1}$ (VVD) which may result from increased drag due to velum growth. When swimming in straight lines, larvae ascend and descend (sinking) only by rotating around the vertical axis, and display much faster swimming speeds than during helical swimming. The range of swimming speeds increased with larval age and varied during ascent between 0.72 and 1.27 mm $s\sp{-1}$ (LVU) and during descent between 0.94 to 1.73 mm $s\sp{-1}$ (LVD).en_US
dc.descriptionI concluded that helical motion favours feeding while restricting vertical distribution of larvae. Therefore, this behaviour can enhance retention of larvae in particular areas. Fast sinking and rising can affect vertical positioning in response to immediate changes in the environment. Young larvae swim slowly, are more buoyant, and have higher lipid levels than older larvae. As larvae grow and density increases due to shell deposition, swimming becomes more energetically costly. At intermediate stages lipids are lowest, increasing again before metamorphosis. I showed that the proportion of triacylglycerides (TG) to total lipids was greatly reduced from eggs (43%) to the formation of Prodissoconch I (29%) and during the Prodissoconch II at 13 days (8%), increasing again in late Prodissoconch II at 22 days (20%).en_US
dc.descriptionAt a larger scale, I monitored vertical distributions of early veligers in a series of mesocosm simulations that included diel light cycle, food availability and salinity stratification. Diel vertical migrations occurred in well mixed food conditions in a 10 m water column, corresponding to the classical nocturnal ascent of most microzooplankton. Larval mean depth was found to vary between a minimum of 2.8 m at night and a maximum of 6.3 m during the day. However, migration of larvae appear to be suppressed in the absence of food and with stratified food in salinity gradients. The observed diel migrations in the mesocosm simulations were comparable to those found in mixed and stratified areas of the Bay of Fundy and Baie de Chaleurs.en_US
dc.descriptionBehavioural traits and larval condition influenced the vertical distribution of larvae on the scale of my observations, and responses of larvae to food availability and diel light cycles resembled those in nature. My studies are a first step to establish a behavioural baseline for the early life history of this unique and valuable pectinid. My results provide new techniques and insights to address questions of larval ecology of marine invertebrates at intermediate scales comparable to the natural environment.en_US
dc.descriptionThesis (Ph.D.)--Dalhousie University (Canada), 1996.en_US
dc.languageengen_US
dc.publisherDalhousie Universityen_US
dc.publisheren_US
dc.subjectBiology, Ecology.en_US
dc.subjectBiology, Oceanography.en_US
dc.subjectBiology, Zoology.en_US
dc.titleEarly life history traits of Placopecten magellanicus (Gmelin): Behaviors, lipid condition and vertical distribution of veligers at micro- and meso-scales.en_US
dc.typetexten_US
dc.contributor.degreePh.D.en_US
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