Ecological engines: Finescale hydrodynamic and chemical cues, zooplankton behavior, and implications for nearshore marine ecosystems
Dynamic and ephemeral resource patches (on fine temporal and spatial scales) are fundamental to the life success of plankton populations - and thus to the overall health and vitality of coastal marine ecosystems. Here we have employed various tools from experimental fluid mechanics to recreate ecolo...
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| Format: | Dissertation |
| Language: | English |
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ProQuest Dissertations & Theses
01-01-2014
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| Online Access: | Get full text |
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| Summary: | Dynamic and ephemeral resource patches (on fine temporal and spatial scales) are fundamental to the life success of plankton populations - and thus to the overall health and vitality of coastal marine ecosystems. Here we have employed various tools from experimental fluid mechanics to recreate ecologically-relevant hydrodynamic and chemical conditions in a recirculating flume system for zooplankton behavioral assays. A laminar, planar free jet (the Bickley jet) is employed to create finescale free shear layers and thin, sharp-edged layers of both beneficial and toxic phytoplankton exudates. Planar particle image velocimetry (PIV) and laser-induced fluorescence (LIF) are used to quantify the concentration and velocity fields allowing us to fine-tune experimental parameters to match chemical and fluid mechanical conditions reported in situ. Subsequent behavioral assays with a variety of zooplankton species, each with unique morphologies, ecologies, and life histories, consistently reveal statistically significant changes in behavior. We seek to understand how individual behavioral responses of zooplankton to various sensory cues on the finescale (<1 m) potentially drive ecological processes in the coastal ocean on the submesoscale (<1 km). In the first part of this study, we investigated how dispersed estuarine crab larvae can potentially optimize long term (habitat selection) and short term (foraging) behavioral needs by sensing and exploiting the information contained in multi-directional free shear flows. Analyses of digitized trajectories from free-swimming Panopeus herbstii (the Atlantic mud crab) megalopae established orientation-specific behavioral shear strain rate thresholds (0.04 s-1 upwelling flow, 0.07 s -1 downwelling flow, 0.1 ss-1 horizontal flow). These thresholds are seen to significantly influence larval behavior through changes in path kinematics (relative swimming speed, turn frequency) and gross path characteristics (net-to-gross-displacement ratio, NGDR, vertical-net-to-gross-displacement ratio, VNGDR, and proportional residence time, PRT). These larval responses are likely associated with foraging and sampling behaviors in the region surround shear layers in which the coherent shear flows acts as a cue to restrict search volume in hopes of exploiting some coincident or nearby cue and/or resource patch, typical features in fronts and clines. The exploitation of sensory cues contained in finescale patches is likely an important means by which dispersed larvae can couple behavioral needs and processes operating on disparate time and space scales (i.e. foraging and finding suitable settlement habitat) and has important implications for structuring coastal marine ecosystems. In the second part of this study, thin layers of toxic phytoplankton (cryptic blooms) were modeled for behavioral assays with calanoid copepods to examine the effects of dissolved toxins, copepod species, and sympatry versus allopatry in behavioral response trends. The sympatric (geographically co-occurring) Acartia tonsa and the allopatric (geographically separate) Temora longicornis were exposed to thin layers of algal exudates from the toxic dino agellate Karenia brevis (equivalent cell concentration: 1 - 10,000 cells=mL). Behavioral response trends with increasing K. brevis concentration revealed extreme avoidance behaviors for both species. Trajectories of the sympatric A. tonsa became more diffuse and erratic, whereas trajectories of the allopatric T. longicornis became more linear and ballistic, on average. As trophic mediators linking primary producers and higher trophic levels, copepods can significantly influence harmful algal bloom (HAB) dynamics and modulate large scale ecological effects through their behavioral interactions with toxic blooms. Finally, in the last part of this study, we investigated how finescale hydrodynamic and chemical cues commonly associated with thin planktonic layers affect individual behavioral processes in Antarctic krill (Euphausia superba). Analyses of digitized trajectories revealed a behavioral shear strain rate threshold of 0.02 s-1 that is seen to significantly influence krill behavior through changes in path kinematics. Slight increases in proportional time spent in the shear layer and significant increases in time spent in the phytoplankton layer suggest that finescale hydrodynamic and chemical cues associated with thin layers enable krill to hone in on a particular resource patch with greater effectiveness and are likely a potential mechanism generating patchiness in krill populations. We have shown that individual behavioral processes could help explain higher frequency variability in krill population dynamics. |
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| ISBN: | 9781321178906 1321178905 |