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dc.contributor.advisorLamare, Miles
dc.contributor.advisorCornwall, Christopher
dc.contributor.advisorPilditch, Conrad
dc.contributor.authorHoulihan, Erin
dc.date.available2019-06-12T21:07:43Z
dc.date.copyright2019
dc.identifier.citationHoulihan, E. (2019). Effects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions (Thesis, Master of Science). University of Otago. Retrieved from http://hdl.handle.net/10523/9377en
dc.identifier.urihttp://hdl.handle.net/10523/9377
dc.description.abstractMacroalgae are able to modify their local environment via biological processes, thereby creating a diffusive boundary layer (DBL) where the chemical and physical environment differs from the overlying bulk seawater. In slow flow environments, the DBL has the potential to modulate effects of reduced seawater pH associated with ocean acidification (OA). OA poses a major threat to marine ecosystems and particularly to calcifying organisms. While implications for macroalgae and corals in the DBL have been studied, the effects on invertebrates settling and inhabiting the DBL are not well understood. This study examines the oxygen and pH conditions within coralline algal DBLs that change as a result of irradiance, flow and bulk seawater pH, in order to understand the effects of these variable conditions on growth of juvenile sea urchins in the DBL. Oxygen concentrations, used as a proxy for pH based on previous research, were measured above crustose coralline algal surfaces to determine DBL thickness and pH levels within the DBL. Newly settled juvenile sea urchins Pseudechinus huttoni were subsequently grown in these conditions for up to 11 days. Morphological measurements (test diameter and spine length) and scanning electron microscopy were used to examine growth and calcification of sea urchins. Seawater pH levels above CCA varied as a result of irradiance, flow and bulk seawater pH. In static flow, CCA increased pH at its surface up to approximately 0.8 units above the overlying bulk seawater in the light, but only decreased pH up to nearly 0.09 units below bulk seawater in the dark. DBLs were thickest at zero or slow flow (1 cm s-1) in the light. pH levels in the DBL varied from approximately pHT 7.4 to 8.6, but there was no strong effect of these varying pH levels within the DBL on post-settlement growth of P. huttoni juveniles. Life in the diffusion boundary has allowed juveniles to adapt to grow and calcify in naturally fluctuating pH environments. This finding supports observations seen in other juvenile sea urchins, and is significant because it indicates that the early post-settlement stage may not be as sensitive to OA as the larval stage, where negative effects have been previously documented. Life in thick diffusion boundary layers above CCA in slow-flow fjord environments may have increased tolerance of juvenile P. huttoni to reduced bulk seawater pH, thereby conferring greater resilience to future ocean acidification conditions.
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherUniversity of Otago
dc.rightsAll items in OUR Archive are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectocean
dc.subjectacidification
dc.subjectcoralline
dc.subjectalgae
dc.subjectdiffusion
dc.subjectboundary
dc.subjectlayers
dc.subjectjuvenile
dc.subjectsea
dc.subjecturchin
dc.titleEffects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions
dc.typeThesis
dc.date.updated2019-06-12T19:44:47Z
dc.language.rfc3066en
thesis.degree.disciplineMarine Science
thesis.degree.nameMaster of Science
thesis.degree.grantorUniversity of Otago
thesis.degree.levelMasters
otago.openaccessOpen
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